CA2109990C - Direct delivery in-situ diffuser cleaning - Google Patents

Abstract

This disclosure relates to aeration, especially biological treatment of wastewater with fine pore diffusers and in situ cleaning of these diffusers with liquid and/or gaseous cleaning fluids supplied to the diffusers through cleaning fluid channels that respectively have separate and direct connections to plural diffusers. Aeration and cleaning of fine pore diffusers is described in which cleaning fluid is conducted from a source of such fluid to a multiplicity of diffusers via a flow path which is separate from a flow path which conveys aeration gas to the diffusers. Methods of fabricating aeration gas distribution assemblies are also disclosed. One such method involves securing to an aeration gas distribution conduit at least a portion of a cleaning fluid distribution channel which includes one or more cleaning fluid distribution conduits and further includes connectors coupled to the cleaning fluid distribution conduits. The connectors are spaced longitudinally along the cleaning fluid distribution conduits at the same intervals as, and are connected to, the plenums. Another method comprises fabricating a cleaning fluid conduit having longitudinally spaced tee connectors coupled thereto. An aeration gas conduit having longitudinally spaced plenums secured thereto is fabricated, and such plenums are have holes for receiving the tee connectors coupled to the cleaning fluid conduit. The invention effectively and economically brings cleaning fluid in contact with diffusion elements without lengthy interruptions in wastewater treatment, complicated processing sequences and back-flow of wastewater through the elements, and can be used with diffusers having back-flow prevention capabilities, including membrane diffusers.

Description

3 The invention relates to aeration of aqueous liquids in 4 water impounds, preferably in tank-type processes, with fine pore diffuser's. In a preferred embodiment, it relates to 6 biological treatment of wastewater including aeration with fine 7 pore diffusion elements and in situ cleaning of such elements 8 with cleaning fluids that comprise liquids and/or gases, 9 including vapors.

HACRGROUND OF THE INVENTION
16 The aeration of waste liquid media, including for example 17 domestic sewage and industrial wastewaters, using submerged 1g aeration devices, is an old art. A common aeration device is 19 the fine pore diffuser. It transfers oxygen to wastewater by producing in the wastewater a discharge of small bubbles of a 21 treatment gas such as air or other oxygen-containing gas.

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1 In a fine pore diffuser, the component which actually 2 produces the bubbles is a porous medium, sometimes referred to 3 as a diffusion element, through which aeration gas received in 4 the diffuser is forced into the wastewater. Porous media of various types have been used for this purpose.

6 MPDEs (multi-pore' diffusion elements), the porous media 7 employed in fine pore diffusers of the MPDE type, have been 8 used in various forms for many years . These elements have been 9 made for example by sintering of ceramic grains in the form of square or rectangular plates, as was popular from the 1920s 11 through the mid-1950s, and to a lesser extent in the late 1950s 12 and 1960s. An MPDE diffuser in which the element was formed of 13 grains sintered in a dome shape was introduced in the mid-14 194os, and enjoyed growing popularity in the 195os, 1960s and 1970s. Diffusers with flat, disk-shaped elements formed of 16 sintered ceramic or plastic grains were used in the 1970s and 17 became popular in the :L980s. Voids between the sintered grains 18 provide gas passages through which aeration gas may flow and 19 discharge from an upper surface of the diffuser as small gas bubbles. Membrane fine pore diffusers, formed from sheet-like 21 webs of synthetic elastomeric material, became popular in the 22 1980s. These webs, which may be of circular, rectangular, 23 square or other shape, as viewed in plan view, have many small 24 gas passages extending through them for discharging small bubbles.

26 Fouling of submerged fine pore diffusers is an old 27 problem. Organic and/or inorganic foulants tend to 28 progressively foul the diffusion elements at the point of 29 release of aeration gas into the wastewater, and may also foul the air passages internally. Such fouling can impair the 31 uniformity of gas distribution from aeration devices, and can 32 increase the pressura_ differential required to drive the 33 aeration gas through the aeration devices at a given flow rate.

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1 The use of gas cleaning to confront the fouling problem 2 received limited attention during the 1930s, 1940s and early 3 1950s. Early efforts concentrated on the cleaning of MPDEs. In 4 1939, W. M. Franklin cleaned the diffusers in several tanks of a wastewater treatment plant in Charlotte, North Carolina, 6 introducing the cleansing gas through the same piping system 7 which normally supplied air to the plenums for the diffusers.

8 Based on his relatively few applications of cleaning gas at 9 Charlotte, Franklin reported that the method was successful.

See W. M. Franklin, "Purging Diffuser Plates With Chlorine,"

11 Water Works & Sewerage:, June 1939, pages 232-233.

12 Further trials were made by R. B. Jackson at Jackson, 13 Michigan. The initial runs reportedly gave satisfactory 14 results. See R. B. ,:fackson's article entitled "Maintaining Open Diffuser Plates With Chlorine," Water Works & Sewerage, 16 September, 1942, pages 380-382. However, the last attempt 17 reported in the article failed completely and inexplicably.

18 Franklin's and Jackson's articles were followed by trials 19 at major wastewater treatment plants in Chicago and New York.

In these trials it was found that the technique failed to clean 21 the diffusers. Also, it was disclosed that the attempts at gas 22 cleaning in Chicago and New York had actually impaired the 23 diffusers by increasing their permeability and making them more 24 difficult to clean by other methods. See the "Manual of Practice No. 5," Federation of Sewage and Industrial Wastes 26 Associations, Champaign, Illinois, 1952, pages 60-61.

27 In 1951, E. P. C:oombs, inventor of the ASL (Activated 28 Sludge Limited) dome diffuser and then managing director of 29 ASL, spoke at a meeting of the Institute of Sewage Purification. His remarks included a warning against the use 31 of gas cleaning on the grounds that it could clean some but not 32 all of the pores of the diffusion elements and thus produced 1 only a very temporary effect. In a guide to cleaning of MPDEs 2 which was apparently first circulated in January 1953, ASL made 3 clear that use of gas cleaning in their diffusers was 4 definitely not recommended.
From the early 1950s forward through 1980, there was a 6 dearth of reports of new activity with respect to gas cleaning 7 of MPDEs. The 1971 edition of Manual of Practice No. 5 did 8 nothing to explain away or dilute the previous unfavorable ~

9 reports. ASL did not back away from their contrary position, but rather insisted that removal of the diffusion elements from 11 the tanks and burning them in a kiln was the only truly 12 satisfactory way of cleaning them. A variety of experts wrote 13 articles and surveys on cleaning methods for MPDEs without any 14 mention whatsoever of gas cleaning.

On November 4, 1980, Frank L. Schmit, David T.

15 Redmon, and Lloyd Ewing filed U.S. Patent Application 17 No. 203,834. ~ b i s application issued May 18 10, 1983 as U.S. Patent No. 4,382,867 entitled "In Place Gas 19 Cleaning of Diffusion Elements" and disclosed a method of cleaning MPDEs in place with cleaning gas while submerged in 21 liquid media by applying said cleaning gas intermittently or 22 continuously to said diffusion elements between predetermined 23 limits of DWP (dynamic wet pressure) or BRP (bubble release 24 pressure) through flow regulation means and plenums for the diffusion elements. On November 5, 1980, Schmit, the President 26 of WPCC (Water Pollution Control Corporation) , gave a speech to 27 the EPA/WWEMA (U.S. Environmental Protection Agency/Water and 28 Wastewater Equipment Manufacturers' Association) Innovative 29 Alternative Seminar in Chicago, Illinois, in which he discussed WPCC's in-situ gas cleaning process and its effectiveness.

31 Initially, commercializing the WPCC process was difficult.
32 Initial resistance on the part of potential customers, based .:_ 1 mainly on concerns about the efficacy of the process, was 2 consistent with the unfavorable reports reviewed above.

3 However, the WPCC process and apparatus were successfully 4 demonstrated in several plants, and developed a good record with respect to efficacy. Eventually, WPCC's gas cleaning 6 process was recognized as effective, and, by 1992, WPCC had 7 licensed about 150 plants for use of its patented gas cleaning 8 process.

9 The Cummings patent, U.S. Patent No. 5,051,193, entitled "Wastewater Treatment Process," and issued September 24, 1991, 11 to Paul W. Cummings, Jr., discloses processes for cleaning 12 MPDEs with 1 iquid acid solutions . The stated obj ectives of the 13 Cummings processes are to provide better penetration of blocked 14 pores, to reduce the quantity of acid used, and to extend the period of acid-element contact. Cummings discloses two 16 alternative processes requiring a series of manipulative steps.

17 In what we refer to as Cummings' "back-flow mixture"

18 process, an acid gas under pressure is made to fill the 19 aeration piping network, the elements, and their plenums. The pressure in the network is then reduced to allow wastewater 21 from the tank to back-flow into and through the pores of the 22 elements into the plenums and piping to mix with the acid gas.

23 Pressure is then reinstated in the network to force the 24 resultant liquid acid into the pores. There is then a quiescent period of up to several hours, in which there is no 26 significant flow of aeration gas into the wastewater while the 27 acid reportedly "reacts" with the foulants. Then, pressure may 28 again be decreased, to allow further back-flow, and then 29 reinstated to force more liquid acid through the pores. The pulsation and quiescent periods are repeated as many times as 31 necessary.

'~ i. ~~~~~~~' 1 During the foregoing steps, which may consume a number of 2 hours, the flow of aeration gas into the wastewater is 3 negligible, compared t~o the aeration gas requirements of normal 4 wastewater aeration treatment. Finally, sufficient pressure is maintained to force more acid through the pores and into the 6 tank, followed by continuous flow of aeration gas at normal 7 rates. This process requires an investment of considerable 8 time, during which the: aeration gas flow is interrupted.
9 A second alternative procedure disclosed by Cummings, l0 herein called the "ext:ernal mixture" process, employs an acid 11 solution. Prepared .above ground, it is made to fill the 12 aeration piping network, the elements, and the plenums. A
13 slight pressure is maintained to prevent back-flow of 14 wastewater from the i:ank and to keep the acid solution in contact with the foulants. After a quiescent period during 16 which the acid solution reportedly reacts with the foulants for 17 the desired period of i:ime, there may be pulsing and additional 18 periods of quiescent reaction as used in the latter stages of 19 the back-flow mixture process.
Here again, aeration gas flow may be interrupted for 21 hours. Finally a normal flow of aeration gas is re-22 established, and more acid solution is driven out through the 23 pores of the elements.
24 At present, wide--spread use of the Cummings methods has not developed. The method has been available for a few years, 26 but there are very few operating installations. The 27 explanation may lie in the fact that the method is subject to 28 a number of limitation:, shortcomings, and adverse perceptions.
29 One factor which may have discouraged widespread use of the back-flow mixture process is the number of steps and 31 controls which can beg involved, some of which may involve '?'09~Ji~

1 delicate adjustment or balancing of pressures and flows. These 2 include initiation of acid gas flow; controlling the rate of 3 acid gas flow and stopping at proper time to provide proper 4 amount of gas in piping and plenums to achieve proper liquid acid concentration upon subsequent admixture of gas with liquor 6 from tank; reduction of aeration gas flow sufficiently to cause 7 back-flow; reinstating aeration gas flow to flood elements 8 while controlling aeration gas flow to prevent complete 9 expulsion of acid from piping, plenums and elements, controlling pressure within the piping and plenums during 11 quiescent period to prevent further back-flow and expulsion of 12 acid from element inward into plenum; repeating two previous 13 steps as necessary; and reinstating aeration gas flow in such 14 a manner as to produce pulsation.

A concern about tlZe back-flow mixture process arises from 16 the possibility of back-flow of sludge into the element.

17 Depending on the height of the water above the diffusers, 18 substantial driving force could be developed to force smaller 19 solids into the pores, fouling the diffuser. It is not apparent whether the foulants will be pushed out again during 21 cleaning or when the aE~ration gas flow is re-established. See 22 "Aeration -- A Wastewater Treatment Process," WPCF (Water 23 Pollution Control FedE:ration) Manual of Practice No. FD-13, 24 page 56.

Another difficulty, which arises in the use of the 26 Cummings external mixture process, involves the sheer volume of 27 liquid acid required. A typical grid contains hundreds to a 28 few thousand diffusers, and a typical plant has multiple grids.

29 A grid of 1000 dome diffusers with 4" diameter distributor piping would require over 1000 gallons of liquid acid to fill 31 the diffusers and the distributor piping. Also, 1000 gallons 32 of liquid acid represents about eighteen 55-gallon drums, 33 weighing approximately 460 pounds each. Moving these drums ;~~(~!~~J!U

1 about the tank site wi.Ll require hard labor or mechanized drum-2 handling equipment. Elimination of drum handling will require 3 expenditures for larger acid storage tanks and their attendant 4 accessories and safety devices.
An additional concern with both of the Cummings processes 6 arises from the fact that they involve keeping the distribution 7 system partially filled with liquid acid while aeration gas is 8 passing through it. It is anticipated that the passage of 9 aeration gas over and through the liquid acid will strip acid gas from the liquid and convey this acid gas through the 11 diffusers. The que:ation thus arises as to whether, in 12 conducting the Cummings processes, a sufficient amount of acid 13 gas would be conducted through the diffusers so that the 14 diffusers would be cleaned by the resultant cleaning gas-aeration gas mixture :instead of or in addition to the liquid 16 acid mixture. In acid gas cleaning systems, most of the 17 cleaning occurs in the: first 20 minutes of acid gas addition.

18 Therefore, in order that the liquid acid used in the Cummings 19 process might perform most of the cleaning, the question arises as to whether it may be necessary, in order to clean primarily 21 with liquid acid according to Cummings' concept, to fill the 22 distribution system with liquid acid in considerably less than 23 20 minutes.

24 Employing the above example of a grid of 1000 dome diffusers with one foot distribution spacing, application of 26 the external mixture method to fill the diffusers and the 27 distributor piping with 1000 gallons of liquid acid in the 28 space of, for instance, 15 minutes would require pumping 67 29 gallons per minute of liquid acid. High rate pumping results in increased safety concerns. The high volume rate of acid 31 pumping and the rapid switching between drums during the 32 pumping process would increase the possibility of personnel 33 being exposed to spills and splashing of the acid solution.

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1 Here again, provision of large acid storage tanks with their 2 attendant accessories and safety devices could prove necessary 3 to attain acceptable :safety levels.
4 Another issue which may surface upon intensive use of the Cummings methods is whether it can be conveniently be 6 determined when the diffusers have been cleaned. In line with 7 the recommendations in the above-identified Schmit et al 8 patent, Cummings suggests monitoring the condition of the 9 diffusion elements, prior to cleaning, through the use of certain measuring devices which are capable of sensing the DWP

11 (Dynamic Wet Pressure) across the elements. In gas cleaning, 12 one can continue to monitor DWP during cleaning. However, DWP

13 cannot be sensed during the quiescent conditions employed 14 during liquid cleaning according to the Cummings patent. It may also happen that, wen when there is gas flow during liquid 16 acid cleaning as suggested by Cummings, that DWP measuring 17 systems will not give accurate indications as to whether the 18 elements have been fully cleaned until most if not all of the 19 residual liquid acid has been driven from the system and the plant has returned to normal, stable operation. This could 21 require a period of hours. If this is the case, then whenever 22 treatment with a given batch of acid has been completed, there 23 will be a delay in determining whether the elements have been 24 fully cleaned, and whether or not a fresh batch of acid will have to be prepared for use in a subsequent cleaning step.

26 When soaking elements with liquid according to the 27 Cummings processes, there is no appreciable aeration gas flow 28 for extended periods. Interruptions of several hours are 29 likely, during which the amount of treatment of wastewater BOD

is greatly reduced. This is a distinct disadvantage when the 31 plant is operating near its capacity or in an overloaded 32 condition.

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1 If, during use of the Cummings system-liquid-flooding 2 process, one were to repetitively alternate between the 3 quiescent periods taught by Cummings and the supplying of some 4 amount of aeration gasp to the wastewater, such as to dislodge foulants, or to provide the microorganisms in the wastewater 6 with some oxygen or to maintain anoxic conditions suitable for 7 phosphorous or nitrogen uptake, the onset of aeration gas flow 8 will drive significant amounts of liquid acid cleaning agent 9 from at least the upper portions of the aeration gas supply pipes and drive it out of the diffusers into the wastewater.
11 Much of the liquid acid driven out of the diffusers in this 12 manner will not therefore have an opportunity for extended 13 contact with the gas passages in the diffusion elements. This 14 acid will represent a waste in the sense that it must be replaced in order to begin another quiescent period.
16 The use of liquid acid solution for cleaning aeration 17 devices in-situ as currently known in the art raises concerns 18 about efficiency, complexity, back-flow of solids, repeated or 19 extended interruption of aeration gas flow, safety, and cost.
The present invention is aimed at reducing these difficulties.

22 In common with prior apparatus for aeration of water, of 23 the type which includes provision for liquid or gas in situ 24 cleaning, the invention, in one of its aspects, comprises a water impound having wall means including a floor for retention 26 of water during aeration thereof. There is also an aeration 27 gas channel including .an attachment for connecting the channel 28 with a source of aeration gas and having a plurality of 29 aeration gas conduits. At least portions of these conduits extend generally horizontally within a zone in the impound 31 which will be submerged in the water during aeration. Multiple 32 fine pore diffusers are mounted at longitudinally spaced 33 intervals along the lengths of, and in communication with the ~~_.fl~~~J~.~
1 interiors of, the generally horizontal portions of the aeration 2 gas conduits. At least: one cleaning fluid channel is provided, 3 and it has an inlet fo:r receiving cleaning fluid from a source 4 of such fluid and at least one conduit for conveying such fluid from said source to said impound for in situ cleaning of the 6 diffusers.
7 The invention includes improvements upon the existing 8 technology in which the cleaning fluid channel or channels 9 include plural members that are within the aforementioned zone of the impound and that respectively have substantially 11 separate and substantially direct connections to plural 12 diffusers. The cleaning fluid channel or channels also define 13 cleaning fluid flow paths which remain substantially separate 14 from the aeration gas channel in those parts of said flow paths which extend from the above-mentioned cleaning fluid channel 16 inlet to said diffusers.
17 In another of its aspects, the apparatus of the invention 18 is of a type which is useful for aeration of wastewater with an 19 aeration gas and comprises a tank having wall means including a floor for holding wastewater which is to be aerated by said 21 aeration gas. The apparatus further includes a multiplicity of 22 fine pore diffusers respectively comprising plenums and 23 diffusion elements which are mounted in a portion of said tank 24 and which will be submerged in said wastewater when said diffusers are in normal operation. There are also cleaning 26 fluid conduits defining one or more cleaning fluid channels.

27 These run from a source of cleaning fluid to the multiplicity 28 of plenums, and are connected with said plenums for 29 simultaneously feeding cleaning fluid from said source to said plenums and to the diffusion elements mounted thereon and for 31 cleaning the diffusion elements. Moreover, there are aeration 32 gas conduits defining one or more aeration gas channels 33 separate from said cleaning fluid channel(s), running from a source of aeration gas to said plenums and connected with said plenums for supp:Lying aeration gas thereto separately from said cleaning fluid.
The invention includes improvements upon existing processes for aeration of water with aeration gas conducted along an aeration gas f low path to and through fine pore diffusers submerged in liquid media. As in prior practice, the process of the present invention comprises conducting a flow of aeration gas from a source of said gas along a first flow path. This aeration gas is delivered via said first flow path to a multiplicity of fine pore diffusers that are submerged, distributed and spaced apart from one another in one or more horizontally disposed arrays in a body of water and that respectively have diffusion elements. Introduction of said aeration gas into said diffusers is accompli:~hed through connections between said first flow path and said diffusers for causing discharge of said aeration gas thrc>ugh said diffusion elements, thereby aerating the water. These elements are subject to accumulation of foulant in and/or on the elements during such discharge. Orc~ariic and/or inorganic deposits tend to form within the elements or at their surfaces, particularly adjacent the liquid media.
However, in accordance with the process of the present invention, a flow of cleaning fluid which is aggressive toward such foulant. .Ls conducted from a source of said cleaning fluid along a second flow path, and is delivered to said multiplicity of diffusers via said second flow path. The flow of cleaning fluid is maintained substantially separate from said first flow path until said cleaning fluid reaches or nearly reaches said diffusers.
Introduction of said cleaning fluid into said diffusers from said second flow path is employed for causing discharge of said <~leaning fluid through said diffusion elements for cleaning each element.

1 The invention also includes methods of assembling 2 apparatus for aeration of water with aeration gas. One such 3 method comprises fabricating aeration gas distributor 4 assemblies by securing to an aeration gas distribution conduit that is useful for defining at least a portion of an aeration 6 gas channel, a plurality of plenums that are disposed at 7 intervals of distance longitudinally along said conduit and are 8 configured to receive diffusion elements useful for aerating 9 water. This method also includes the step of securing to said plurality of plenums one or more cleaning fluid distribution 11 conduits respectively defining a cleaning fluid channel that is 12 substantially separate from said aeration gas channel for 13 supplying cleaning :Fluid to said plenums substantially 14 separately from said aeration gas.

Another method of the invention, for assembling apparatus 16 for aeration of water with aeration gas, also comprises 17 fabricating aeration gas distributor assemblies by securing to 18 an aeration gas disi~ribution conduit that is useful for 19 defining at least a :portion of an aeration gas channel, a plurality of plenums that are disposed at intervals of distance 21 longitudinally along s;~id conduit and are configured to receive 22 diffusion elements useful for aerating water. This method 23 further comprises securing to said aeration gas distribution 24 conduit at least a portion of a cleaning fluid distribution channel which includes one or more cleaning fluid distribution 26 conduits and further includes connectors that are coupled to 27 said cleaning fluid ~~istribution conduits) and are spaced 28 longitudinally along said cleaning fluid distribution 29 conduit (s) at the same intervals as, and are connected to, said plenums.

31 Another method of the invention that is useful for 32 assembling apparatus for aeration of water with an aeration gas 33 comprises fabricating at least a portion of a cleaning fluid L ~.~~~'~~

1 channel comprising cleaning fluid conduit and plural tee 2 connectors positioned at longitudinally spaced intervals along 3 said channel portion, said tee connectors having base legs 4 projecting laterally from said cleaning fluid channel portion.
This method also includes fabricating at least a portion of an 6 aeration gas channel that comprises aeration gas conduit that 7 has a plurality of longitudinally spaced plenums secured 8 thereto. Such plenums are configured to receive diffusion 9 elements, are spaced apart by intervals substantially similar to those of the tee connectors, and have walls with holes 11 therethrough for receiving said tee connector base legs. The 12 cleaning fluid channel. portion is secured to the aeration gas 13 channel portion by securing the tee connector base legs in 14 communication with said holes.
ADVANTAGES OF THE INVENTION
16 The present invention can be employed to effectively and 17 economically bring cleaning fluid in contact with diffusion 18 elements without the need for lengthy interruptions in the 19 supply of aeration gas to the wastewater treatment process.
However, at least some embodiments of the present 21 invention permit interruption of aeration gas flow during 22 cleaning while minimizing wastage of cleaning agent.
23 Certain embodiments of the present invention offer a plant 24 operator the opportunity to achieve greater independence between aeration gas flow and cleaning fluid utilization.
26 Moreover, acid concentration at the diffuser can be 27 controlled to an extent not possible with the Cummings back-28 flow process. The ratio of cleaning fluid flow rate to 29 aeration gas flow rate can be readily altered as desired and very high concentrations can be readily attained.

1 The invention c:an be practiced without complicated 2 processing sequences, that is, fewer steps are required in the 3 cleaning procedure.
4 No back-flow of the wastewater through the diffusers is required. Consequent:Ly, any potential for diffuser plugging 6 which might otherwise result from such back-flow is avoided.
7 The invention is especially useful in systems in which the 8 diffusers have back-flow preventing means. Such back-flow 9 preventers are present: in most membrane type diffusers in use today. Furthermore, back-flow preventers can be used in il diffusers with sintered grain diffusion elements, such as 12 porous ceramic and plastic disk type multi-pore diffusion 13 elements. The above-mentioned Schmit et al U.S. Patent 14 4,382,867 discloses several types of back-flow preventers.
A further advantage of this direct delivery method over 16 the Cummings methods is that when liquid acid is used, less of 17 it is required, as it is unnecessary to fill the aeration gas 18 channels with liquid acid. Thus, less acid is ultimately 19 forced into the wastewater, reducing any potential which may exist for harming the microorganisms in the wastewater.
21 Reduced liquid acid consumption reduces operating cost.
22 As compared to the amounts used in existing liquid 23 cleaning technology, the smaller volume of acid necessary for 24 practice of the invention requires less handling, resulting in improved safety.
26 Direct delivery of cleaning fluid to diffusers allows 27 frequent use of strong cleaning agents even if the submerged 28 air header pipes in the plant are made of material which 29 deteriorates seriously upon repeated exposure to the agent.
Since the agent is delivered directly to the diffusers, the :?~~~~~(~

1 pipes are not exposed to the cleaning agent and only the 2 diffusers need be made of materials highly resistant to the 3 agent. Although this benefit applies to retro-fitting of 4 existing plants which have corrosion-sensitive air header pipes, it also applies in new plants in which use of such pipes 6 is desired.
7 The apparatus and method of the present invention also 8 share the advantage of versatility. They permit use of liquid 9 and/or gaseous cleaning fluid.
It is not uncommon for the compression of aeration gas to 11 increase its temperature well above ambient and well above that 12 of the wastewater. Because the aeration gas and cleaning fluid 13 flow paths are separated over substantial portions if not 14 substantially all of their respective lengths, the invention can be used to inhibit interchange of heat or components, 16 reactive or unreactive,, between the cleaning fluid and aeration 17 gas, at least until they reach the diffusers. This, for 18 example, can reduce heat losses from the cleaning fluid to the 19 aeration gas, and facilitates delivery of cleaning fluid that is hotter than the aeration gas to the diffusers.
21 In one embodimeni:, cleaning fluid is conducted along a 22 second flow path surrounded by but separate from a first flow 23 path that conveys aeration gas to the diffusers. Because of 24 the compression-induced increased temperature of the aeration gas relative to the wastewater, very hot cleaning fluid in the 26 second flow path may be surrounded by aeration gas in the first 27 flow path which is of lower temperature than the cleaning fluid 28 but of higher temperature than the wastewater. This limits the 29 temperature gradient across the wall of the conduit which separates the first and second flow paths, thus limiting heat 31 losses from the cleaning fluid to wastewater surrounding the 1~ _ ~ i ~999~
first flow path, and facilitates delivery of cleaning fluid that is hotter than the wastewater to the diffusers.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a. schematic diagram including a fragmentary view of a sewage aeration system including a cleaning fluid system with conduits defining cleaning fluid channels to pass cle~~ning fluid to said plenums and a aeration gas supply system including conduits defining aeration gas channel; separate from said cleaning gas channels to conduct aeration gas to said plenums and thence to the elements.
Figure lA is an enlargement of Figure 1 to show the conduits in greater detail.
Figure 2 is a perspective view of portions of the conduits and a portion of the diffusers shown in Figure 1.
Figure 3 is a transverse, vertical cross-section through one of the diffusers of Figure 2 taken on section line 3-3.
Figure 3A is an enlargement of Figure 3 to show in detail a connection between the plenum of Figure 3 and a cleaning fluid channel. in communication therewith.
Figure 4 is a sectional view taken on section line 4-4 of Figure 3A.
Figure 5 is an exterior, side view of the diffuser shown in Figures 2 and. 3 and the cleaning fluid channel of Figures 2, 3 and 4.
Figure 6 is a sectional view, similar in aspect to Figure 2, disclosing an additional embodiment of the invention similar to that illustrated in Figures 1-5 but having the cleaning gas channel mounted within the aeration gas channel.

~ u~; 990 Figure 6A is a:n enlargement of Figure 6 to show details of the connec'~~ion between the cleaning gas channel and the diffuser plenum.
Figure 7 is a schematic diagram including a fragmentary view of ;~ sewage aeration system similar to Figure 1 but having the cleaning fluid channels partially enclosed within the aeration gas channels.
Figure 8 is a ~~erspective view of portions of the conduits, a portion of the diffusers and a portion of the fluid conduit entry joints shown in Figure 7.
Figure 9 is an exploded and partially cut-away view of one of the fluid conduit entry joints shown in Figure 8.
Figure 10 is a cross-section of a segment of the cleaning fluid conduit within a segment of the aeration gas conduit shown in Figure 7 and 8, a portion of the diffusers shown in Figures 7 and 8, and the fluid conduit entry joint shown in Figures 8 and 9.
Figure 11 is an exploded and partially cut-away view of one of the connections between the cleaning fluid conduit and the plenum and one of the connections between the aeration gas conduit and the plenum shown in Figure 10 Figure 12 is a cross-section of one of the joints between two segments of the cleaning fluid conduit within the aeration gas conduit shown in Figure 10.
DESCRIPTION OF VARIOUS. AND PREFERRED EMBODIMENTS
The invention may be employed in the aeration of waters with negligible to substantial amounts of dissolved and/or suspended solids, such as slurries or sludges. For example, the invention may be applied to waters which, after aeration, will be employed as drinking water, as industrial process water or for other uses. However, the principal applications of the invention are expected to be the aeration of various forms of w~.~~~~',~

1 wastewaters, including both domestic and industrial 2 wastewaters, such as those resulting from chemical and "food"

3 processing, the latter including for example agricultural, 4 canning, brewery and slaughterhouse applications. The preferred application of the invention is in connection with 6 activated sludge processing of mixed liquors, combinations of 7 return sludge and incoming domestic wastewater which may 8 include minor proportions of industrial waste. However, the 9 invention may be employed with virtually any form of wastewater.

11 The aeration may be conducted, and therefore the water 12 impounds of the apparatus of the invention may include, 13 virtually any natural or manmade passage or partial enclosure, 14 such as a lake, river, or lagoon, and preferably a tank.

Typically, the water impounds involved in the invention will 16 include "wall means" including at least a bottom "wall" but the 17 term "wall" is used here in a broad sense to include any sort 18 of underlying and at :Least partially surrounding containment 19 surface or barrier, whether of earth, asphalt, plastic, concrete, metal or other material. The bottom wall may have 21 any shape (including configuration), such as flat, dished, 22 ridge and furrow or any other regular or irregular shape. The 23 impound may also have side walls which may for instance be 24 slanted but are preferably upright. Impounds having either distinct sections within a given tank or plural tanks to 26 provide varying conditions of treatment, such as varying oxygen 27 contents in the wastewater, including anoxic zones where 28 desired, may be employed. The most preferred form of water 29 impound is a concrete tank equipped for biological treatment of domestic and/or industrial wastewater by a purification process 31 which involves biological treatment.

32 For purposes of the present invention, an aeration gas 33 channel is any reasonably durable and substantially leak-proof 1 system of conduit and/or other devices for conveying aeration 2 gas in sufficient quantities from a source of such gas to the 3 diffusers in a submerged portion of a water impound. The 4 aeration gas to be conveyed by such channel may be any gas (including true gases,. vapors and mists entrained in gases), 6 suitable for supplying oxygen to the water and/or its contents.
7 Examples include oxygen, oxygen containing gases such as air 8 and oxygen- or ozone-enriched air and gases which react to 9 release oxygen. Suitable sources of such gases are, typically, compressors or blowers which draw air through a filter system 11 from the atmosphere. I~owever, where necessary or desirable, at 12 least a portion of the aeration gas may be drawn from a tank or 13 a reactor, such as a source of oxygen, an ozone generator or a 14 source of other gases.
While the aeration gas channel will most typically be 16 constructed with various types of conduit, the channel may 17 include or communicate. with various other devices to assist 18 with the primary function or selected other functions to be 19 performed by the aeration gas channel. Such conduit may vary from rigid to flexible conduit if properly supported. Any 21 suitable material of construction may be used to fabricate the 22 conduit, including resin, concrete, metal or other materials.
23 Circular, rectangular or other cross-sections may be employed 24 as desired.
As viewed in plan view, the conduit of the aeration gas 26 channel may be laid out in any suitable plan, pattern or 27 layout. Typical and preferred layouts include multiple lines 28 of conduit laid out substantially parallel to one another in 29 order to feed aeration gas to diffusers. Such parallel lengths may for example be arranged in elongated rectangular tanks with 31 most of the parallel lines of conduit running either cross-wise 32 or lengthwise with respect to the long dimensions of the tanks.
33 There will be a certain lateral spacing between the parallel 1 lines of conduit, which is at least partly based on the number 2 of diffusers which will be used. Within a given portion of the 3 horizontal plan view of the tank, the parallel lines of conduit 4 may be spaced apart by like distances. Elsewhere in the tank, different or variable spacings may be employed, especially 6 where lesser amounts of aeration gas, and therefore diffusers, 7 are required. When employing tanks that are circular in plan 8 view, the lines of conduit may be laid out in a radial pattern 9 or in concentric circles of successively increasing circumference.

11 As viewed in elevation, the conduit of the aeration gas 12 channel may be at different elevations relative to the floor of 13 the water impound. For example, the conduit may be installed 14 in, on or above the floor or a combination of the foregoing.

While it is possible to position the majority of the conduit 16 above the wastewater surface, it is preferred to have the 17 majority of such conduit submerged in the wastewater above but 18 relatively near the floor of the water impound. While it is 19 generally preferred that the aeration gas channel include substantially horizontal portions to support diffusers, such 21 channel may also have significant portions of the conduit in 22 non-horizontal orientations. For example, there may be 23 downcomer pipes to carry aeration gas from above the water 24 surface to horizontal :manifold and distribution pipes near the water impound floor.

26 Persons skilled in the art are aware of and knowledgeable with 27 respect to the fabrication and installation of various types of 28 accessory hardware employed with aeration gas channels, 29 including for example various types of supports. These include not only swing mounts, which supply aeration gas to submerged 31 diffusers and permit raising the diffusers out of the water for 32 servicing, but also fixed mounts. The latter include various 33 forms of brackets and stands which may be anchored to the walls 34 of a tank, including the walls and/or the floor and preferably 1 mainly the latter. Persons skilled in the art are also skilled 2 in applying various forms of couplings, expansion joints, gas 3 flow control valves, and the like. Also, it is known to 4 provide such channels with valve controlled outlets useful for purging water from low points in the system.
6 The preferred aeration gas channel for the present 7 invention employs rigid plastic conduit, such as PVC
8 (polyvinylchloride), having a circular cross-section of about 9 4" diameter mounted within about 18 inches above the concrete floor of an aeration tank on fixed floor-mounted brackets or 11 stands laid out in what is referred to by those skilled in the 12 art as a grid pattern ~~omprising vertical downcomers to supply 13 aeration gas to horizontal manifold pipes which in turn direct 14 the aeration gas into groups of parallel and horizontal distribution pipes on which diffusers are mounted.
16 Many types of fine pore diffusers are potentially useful 17 for practicing the invention. A partial listing and a number 18 of specific examples of such devices are provided in the Design 19 Manual for Fine Pore Aeration Systems published by the Untied States Environmental Protection Agency Center for Environmental 21 Research Information, Publication No. EPA/625/1-89/023, 22 Cincinnati, Ohio, September 1989, pages 2 et seq. Included in 23 the non-exhaustive listing in this publication are diffusers in 24 which the diffusion elements are: porous ceramic plates, discs, domes and tubes; rigid porous plastic plates, discs and tubes;
26 non-rigid porous plastic tubes; and perforated membranes in the 27 form of tubes, discs and rectangular sheets. Each of these is 28 available with "fine pores" which are suitable for discharging 29 gas into water to create fine gas bubbles therein.
By way of illustration, typical bubbles generated by fine 31 pore diffusers range in size up to about 0.2 inches (5 32 millimeters) or less when discharged from a new or thoroughly 1 clean diffuser in clean water at a gas flow rate of two 2 standard cubic feet per minute per square foot of active gas 3 discharge surface of the diffuser. However, it should be 4 understood that the babble size may increase with increasing flow of gas through the diffuser. Also by way of illustration, 6 a typical surface tension head loss for a fine pore diffuser is 7 about two inches of water gauge or more.
8 On the other hand, it should be understood that the 9 practice of the present invention is not limited to fine pore diffusers that are currently available in this advancing 11 technology, nor to those strictly complying with the above 12 characteristics. Rather, the invention is concerned with 13 present and future devices having pores suf f iciently fine to be 14 relatively efficient aerators and also having susceptibility to significant fouling and reasonably successful in situ fluid 16 cleaning.
17 It is the diffusion element which is primarily responsible 18 for the bubble producing function of a fine pore diffuser.
19 Without any intention of limiting the foregoing description of fine pore diffusers useful in the practice of the invention, we 21 provide below a discussion of some of the characteristics of 22 diffusion elements which are common to the diffusion elements 23 and diffusers which are most popular in current day practice.
24 Such diffusion elements typically include an apertured wall which may be of ceramic, polymeric or other material.
26 Inorganic and organic polymers, including natural and/or 27 synthetic polymers in resinous, elastomeric or other forms, are 28 among those which may be used to fabricate the apertured walls 29 in any suitable shape.
While fine pore diffusion elements of virtually any shape 31 may be employed when practicing the invention, the most popular 1 fine pore diffusion elements in present day practice appear to 2 be those which are plate- or disc-shaped. In plan view, these 3 typically exhibit rounded (including circular), square or 4 rectangular outlines. The tops and bottoms of plate or disk diffusers, when viewed in vertical cross-section, are generally 6 horizontal, which include both flat and non-flat surfaces.

7 Among the non-flat generally horizontal surfaces that are known 8 are those characteristic of the center and boundary treatments 9 disclosed in U.S. Patents 4,261,932 and 4,261,933, both to Ewing et al and assigned to WPCC (Water Pollution Control Corp.

11 of Milwaukee, Wisconsin), the assignee of the present patent.

12 When viewed in vertical cross-section, the peripheries of 13 such plate or disc shaped diffusers may include stepped edges.
14 Such edges may for example be the result of an edge permeability treatment., such as shown in Ewing et al U.S.
16 Patent No.4, 288, 395, a:Lso assigned to WPCC, or in Veeder's U.S.
17 Patent No. 4,046,845, which respectively show the stepped 18 portion of the element periphery underlying or overlying a 19 sealing member intended to provide a gas tight seal between the element and its plenum.
21 However, it should be understood that no permeability 22 treatment of the above-described type is required either in the 23 center, boundary or peripheral portions of the diffusion 24 element. Thus, elements with non-stepped edges may be readily employed. This includes plain-edged elements and those with 26 peripheral features other than stepped edges, including for 27 instance the integral sealing rings included in the peripheries 28 of certain types of membrane diffusers. A wide variety of 29 forms of integral seals may be included in the applicable diffusion elements, whether the latter are of the membrane type 31 or not.

~~1~~~~~~) 1 Another form of diffusion element which has enjoyed 2 considerable popularit:y in the past and which is still used in 3 some locations today is the dome-type diffusion element.
4 Introduced in the U.K. in a four inch diameter version which 5 was used in the 1940s and early 1950s, the domes were 6 redesigned in a seven inch version in the mid 1950s which was 7 eventually employed in many countries throughout the world by 8 the 1970s. These diffusers are shown for example in Coombs' 9 U.S. Patent 2,639,131 and Branton's U.S. Patent 3,532,272.

10 Still another form of diffusion element which was popular 11 in the past is the porous tube type. It enjoyed its widest use 12 before the dome diffuser reached its zenith of popularity.

13 Porous tubes are discussed in Miles Lamb's article, "Designing 14 and Maintaining Porous Tube Diffusers," Wastes Enqineerinq, 15 September, 1954, pp. 405-410 and 413. At one time these 16 diffusers were made mainly of porous carbon, then porous 17 ceramic and eventually porous plastic (including wound saran 18 cord) material. As shown by the above-mentioned 1989 EPA

19 Design Manual, various forms of ceramic, rigid porous plastic, 20 perforated membrane and non-rigid porous plastic tube diffusers 21 are still in use today, but these are to be distinguished from 22 the fundamentally different tubing type diffusers of AB

23 Marketech, Hinde and other manufacturers.

24 Contemporary diffusion elements, irrespective of their 25 shape, generally include some form of gas transmission passages 26 through their walls. The passages may be formed in different 27 ways. For example, formation of the passages may be inherent 28 in the method of formation of the wall. By way of 29 illustration, when the wall of a diffusion element is formed by sintering a compact formed from compressed grains of ceramic or 31 plastic material, the particle size and amount of compression 32 are controlled so that. the grains are not fully compacted in 33 the resultant part. Thus, there remains a void volume within ~~ ~~:~~~I

1 the part which defines passageways leading from one surface of 2 the wall through the interior of the part to its other surface.
3 This void volume provides a myriad of passages of very small 4 dimensions which have been produced as an inherent feature of the production of the element wall.
6 However, formation of the wall and formation of the 7 passages through the wall may constitute separate steps. For 8 example, the passages may be formed subsequent to wall 9 formation, which is typical of the production of membrane type diffusers. A membrane diffuser is typically a sheet or tube of 11 elastomeric material which, when initially produced, is 12 relatively free of apertures that would be suitable for the 13 transmission of aeration gas. After formation of the elastomer 14 into round, square, rectangular or tubular shape, the shaped part is perforated, such as by laser treatment or, more 16 commonly, with ganged cutting knives, to produce gas 17 transmission passages and their associated discharge ports.
18 The foregoing illustrations should be sufficient to 19 demonstrate that the gas passages extending through the walls of fine pore diffusion elements may be arranged in a random or 21 regular manner and may pass relatively directly or relatively 22 indirectly from one surface of the wall to its opposite 23 surface. Also, it should be apparent that the shape of the gas 24 passages can vary widely. They may be branched or unbranched, regular or irregular, and straight or tortuous in elevation and 26 circular or non-circular in cross-section. There is also 27 considerable room for variation in the shape of the gas passage 28 outlets at the gas discharge surface of the diffusion element.
29 Regular or irregular, open or openable and circular or non-circular shapes are a few examples of suitable shapes.
31 In general, the applicable diffusion elements will have a 32 gas discharge surface with sufficient active gas discharge area y 1 and a sufficient number of active gas discharge outlets 2 distributed over that area, so that the element may be 3 described as an "area-release" element. For purposes of the 4 present invention, an area-release type element is one which has a rather substantial active gas discharge area, for 6 example, at least about 20, more preferably at least about 30, 7 and still more preferably at least about 40 square inches, in 8 which there are many gas discharge outlets distributed randomly 9 or regularly throughout most if not all of the area. On average, it is preferred that there should be a plurality of 11 active or working gas discharge passage outlets or ports per 12 square inch of active gas discharge area. If the element is an 13 MPDE (multi-pore diffusion element) of the type described in 14 U.S. Patent 4,382,867,. the gas discharge area of the element may also include inactive outlets which are capable of 16 commencing discharge of gas as element condition and operating 17 conditions change. The outlets, whether active or inactive, 18 are preferably distributed over substantially the entire, or at 19 least the major port: ion of, the available gas discharge surface, and in a patterned or irregular fashion.

21 Gas handling characteristics of fine pore diffusers may 22 for example be expressed in terms of DWP (dynamic wet pressure) 23 or BRV (bubble release vacuum) For explanations of DWP and 24 BRV, see the definitions below. In general, DWP is the preferred basis for characterizing these elements and their 26 degree of fouling, due to the fact that the amount of DWP field 27 data available is believed larger than the amount of BRV field 28 data that is available. However, BRV may be the only basis for 29 quantifying certain types of fouling, such as the formation of biofilms.

31 At present, it <~ppears that the applicable fine pore 32 diffusion elements will exhibit a DWP in the range of about 3 33 to about 20, typically about 4 to about 12 and preferably about 2~.~~~9~

1 5 to about 10 inches of water gauge when discharging air at a 2 flow rate of 2 SCFM per square foot of active gas discharge 3 surface of the diffuser. Similarly, it appears that the 4 applicable elements will generally exhibit a BRV of about 2 to about 15, more typically about 3 to about 9 and preferably 6 about 5 to about 8 inches of water gauge when discharging air 7 into a BRV test probe with an 0.175 inch internal cross-section 8 at a flow rate of about 0.0019 SCFM. The foregoing DWP and BRV

9 values assume that the elements are tested in clear water with the element in a thoroughly clean and preferably new condition.

11 The most preferred fine pore diffusion element for use in 12 practicing the present invention is the commercially available 13 SANITAIRE (TM) diffuser with a ceramic disc MPDE of the type 14 . described in U.S. Patent 4,382,867, fabricated by forming and sintering a compact o:E ceramic granules and glassy binder to 16 produce a 7 or 9 inch diameter by 3/4 inch thick element having 17 the center, boundary and peripheral edge treatments described 18 in said patent and in the other Ewing et al patents identified 19 above. The passages resulting from the void volume within the element have branched, irregular and tortuous shapes with non-21 circular cross-sections. The outlets of these passages at the 22 gas discharge surface of the elements are open, non-circular 23 and irregularly shaped and are distributed irregularly and 24 randomly over substantially the entire upper surface of the element.

26 Under the DWP, BRV and permeability test conditions 27 described above and in the above-mentioned U.S. Patent 28 4,382,867, the preferred fine pore diffusers exhibit a DWP of 29 about 5 to about 8, a BRV of about 5 to about 8 and a permeability of about 15 to about 30. The current design flux 31 rate range for these diffusers is in the range of about 1.25 to 32 about 7.5 SCFM per square foot of active gas discharge surface, 1 and most applications at present are designed with a flux rate 2 of about 3 SCFM/ftZ.
3 In the preferred diffusion elements, the coefficient of 4 variation of BRV across the gas discharge surface is not greater than about 0.25, based on the values of BRV

6 measurements on ten sampling areas of equal area on the gas 7 discharge surface of the element and through the center 8 thereof. These areas may for example be defined by imposing a 9 grid of squares over the area and testing at the centers of the squares so that the test points are spaced apart from one 11 another in both of two different directions. Preferably, the 12 coefficient of variation is less than about 0.15, more 13 preferably less than about 0.05 and still more preferably less 14 than about 0.02.

For purposes of t:he present invention, a plenum is a gas 16 space within a diffuser which affords opportunity for 17 reasonably uniform distribution of gas to the inlets of the gas 18 discharge passages through the walls of the diffusion elements.

19 As employed herein, the term plenum includes not only permanently existing spaces defined by plenum walls and 21 internal surfaces of diffusers having rigid diffusion elements, 22 but also the temporary gas distribution spaces defined by rigid 23 support members and t:he internal surfaces of the distended 24 elastomeric diffusion elements of certain membrane diffusers.

While certain of these diffusers are configured in such a way 26 that the membranes collapse against their holders in the 27 absence of gas pressure, in which condition there may be no gas 28 space present which is identifiable as a plenum, the membranes 29 also expand away from. their supports under gas pressure to provide a temporarily existing plenum during gas flow.

31 As shown in the above-mentioned EPA report, plenums may be 32 positioned in or above the floor of the water impound, and will -.1 'j~ ~9~~~~
1 typically include sealing means and retaining means familiar to 2 those skilled in the art for the purpose of securing the 3 diffusion elements in substantially leak-proof relationship 4 with the plenums. In a preferred embodiment, each diffusion 5 element has its own individual plenum and the plenums are 6 supported upon, and positioned at spaced intervals along, the 7 horizontal portions o:E conduits included in the aeration gas 8 channel. Several illustrative types of plenums are disclosed 9 in Ewing et al U.S. Patent 4,288,394, assigned to WPCC, a l0 particularly preferred form of plenum being shown in Figure 11 11 herein. It includes an arcuate bottom wall which conforms to 12 the arcuate upper surface of the aeration gas conduit. The 13 plenum bottom wall i:a formed as an integral part of a PVC

14 casting, which also includes sonically configured side walls, 15 a peripheral supporting shelf for the element and a side wall 16 with threads for a regaining ring, all of which are described 17 in greater detail below.

18 In the practice of the present invention, a "flow 19 regulator" is a device which controls the rate of flow of 20 fluid, including aeration gas and/or cleaning fluid, into a 21 diffuser. Preferably, the flow regulators are associated with 22 diffusers having plenums, and the flow regulators are 23 preferably the means through which the aeration gas and/or 24 cleaning fluid gain entry to the plenums.

25 Generally, a flow regulator comprises at least one flow 26 control orifice of determinate flow cross-section. The flow 27 cross-section of a regulator is the aggregate cross-section of 28 the flow of fluid through the orifice or orifices which it 29 includes, during operation of the aeration gas or cleaning 30 fluid channel with which the regulator is in operation.

31 The flow regulator may be a passive device with a fixed 32 flow cross-section or may be an active device with a variable 1 flow cross-section. For example, a flow regulator may be a 2 passive device as simple as a single fixed orifice of 3 appropriate size or a plurality of such orifices. Moreover, 4 the flow regulators may include or be combined with valuing means when it is desired that the flow regulator perform a 6 back-flow preventing function. A particularly preferred active 7 flow regulator which includes valuing means is the "duck-bill"
8 type illustrated in Figure 11 herein.
9 Orifice flow cross-sections are selected in such a way that the pressure drops through the regulators will be 11 substantially greater factors than the pressure drops across 12 individual diffusion elements in determining the rates at which 13 aeration gas and/or cleaning fluid are distributed among the 14 diffuser plenums. Persons skilled in the art are able to design and install flow regulators able to distribute flows of 16 aeration gas and/or cleaning fluid among multiple plenums so 17 that the flow rate to a given plenum and its diffusion element 18 will be substantially the same as the flow rate of such gas 19 and/or fluid to the other plenum or plenums connected to the same aeration gas channel and/or cleaning fluid channel.
21 A variety of active and passive flow regulators, with and 22 without back-flow preventing means, are illustrated in Figures 23 5 through 5D of U.S. Patent 4,384,867. The standard plug 24 orifice disclosed in Figures 3 through 5 of said patent and figures 3 and 6 herein is considered suitable for use as a flow 26 regulator for aeration gas in the present invention. However, 27 in the plenums of WPCC's commercial diffuser products, orifices 28 in the form of simple holes drilled through the saddle-shaped 29 bottom walls of the plenums and through the adjoining walls of the aeration gas channel conduits near the lowest points on 31 said bottom walls, have proven quite satisfactory. One-way 32 orifices are preferred for use as aeration gas and cleaning 33 fluid flow regulators in the present invention. However, N -f,~

1 various other forms of flow regulators are known to, or can be 2 devised by, those ski:Lled in the art, and may be employed in 3 practicing the invention.
4 From the foregoing discussion and from the examples of flow regulators found in U.S. Patent 4,384,867, it should be 6 apparent that the elevation of the opening through which a flow 7 regulator discharges fluid into the interior of a plenum may 8 vary. Thus, for examp:Le, when a plug orifice is employed as an 9 aeration gas flow regulator, the discharge opening may for example be elevated above the plenum floor. If the plenum has 11 an arcuate floor with a crown, the discharge opening may be at 12 or near the elevation of the crown. Also, the flow regulator 13 discharge opening can be at the low point of a saddle-shaped 14 plenum floor.
A one-way aeration gas flow regulator having its gas 16 discharge opening at i;including in, on or near) or above the 17 crown of a saddle-shaped plenum floor is considered best at 18 resisting both back-flow of water from the water impound 19 through the diffusion element into the plenum and drain back of cleaning liquid from t:he plenum into the aeration gas channel.
21 On the other hand, a simple orifice at the crown will generally 22 have a small enough cross-section to substantially impede such 23 back-flow and drain-back. Other advantages of the simple 24 orifice, when located at a low point in the plenum, include good capabilities for_ aspirating liquid from the plenum, 26 including both condensate and cleaning liquid. Because the 27 simple orifice is most: economical, it may be considered best 28 overall for some applications.
29 Virtually from the beginning of in-situ gas cleaning of aeration systems in then 1930s, it has been standard practice to 31 direct cleaning fluid to diffusers through the same channel 32 which supplies them with aeration gas. For this reason it was 1 perhaps quite natural that when in-situ liquid cleaning of 2 diffusers was described by Cummings, Jr. in U.S. Patent 3 5,051,193, the aeration gas channel was chosen as a path for 4 delivering cleaning liquid to the diffusers.
Unlike prior aeration apparatus and processes embodying 6 in-situ diffuser cleaning, the present invention employs a 7 dedicated cleaning fluid channel. This channel differs from 8 that described in certain prior art, such as U.S. Patent 9 4,634,312 to Sterzel, which is not related to aeration gas channels or diffusers. Contrary to prior teachings in the art 11 pertaining to in-situ cleaning of diffusion elements of 12 aeration systems, the present invention has demonstrated the 13 advantages of an aeration system having separate aeration gas 14 and cleaning fluid channels. A number of such advantages accrue where the cleaning fluid is a liquid, and the resultant 16 system has the further advantage that it is also useful for gas 17 cleaning of the diffu~~ers.
18 A cleaning fluid channel, in the context of this 19 invention, is any reasonably durable and substantially leak-proof system of conduit and/or other devices for conveying 21 cleaning fluid in sufficient quantities from a source of such 22 fluid substantially directly to the diffusers in a submerged 23 portion of a water impound. The cleaning fluid to be conveyed 24 by such channel may be any liquid or gas (including true gases, vapors and liquid droplets entrained in gases) which is 26 suitable for in-situ cleaning of the diffusion elements of fine 27 pore diffusers.
28 While it is an advantage of the invention that it makes 29 possible the creation of in-situ cleaning systems capable of applying gaseous and/or liquid cleaning fluids to diffusers, 31 not every embodiment of the invention must necessarily be 32 capable of operating with both liquid and gaseous cleaning 1 agents. Thus, it is within the spirit of the invention to 2 build and operate apparatus or conduct processes in systems 3 incapable of applying both cleaning gas and cleaning liquid.

4 Nevertheless the preferred apparatus, processes and methods of the present invention are those which have the capability of 6 employing any suitable cleaning fluid, whether liquid and/or 7 gaseous.

8 Suitable example: of cleaning gases include one or more 9 gaseous (including vaporized) organic and/or inorganic solvent l0 compounds or mixture:: of solvent compounds including those 11 compounds capable of existing as liquids and those capable of 12 existing as gases at 20C and standard atmospheric pressure.

13 Examples include HZOz, CH30H, CH3COCH3 and other volatile organic 14 solvents. But the preferred cleaning gases are those which exist as gases at 20C and which give an acid reaction when 16 dissolved in water, such as for example, S02, S03, C02, C12 C102, 17 HC1, NOx, 03, Br2, and the like, HC1 being particularly 18 preferred. While formic acid is a liquid under normal ambient 19 conditions, like other liquid acids it can be formed into a mist, entrained in a flow of gas and conducted in minute 21 gaseous dispersion t.o the diffusion elements. In such 22 circumstances, the mixture of gas and dispersed particles of 23 liquid acid qualify as cleaning gas for purposes of the 24 invention.

A number of the acid gases mentioned above are readily 26 soluble in water and thus form liquid acids which are quite 27 suitable as liquid cleaning fluids. Among these are S03, HCl, 28 NOX and BrZ, HC1 being the preferred liquid acid. However, the 29 cleaning liquids used in the invention are not limited to acids. For example,, aqueous solutions of NH3, of basic 31 mixtures of NH3 and C12 and of detergents may be employed for 32 the cleaning of some: diffusers, for example the membrane 33 diffusers. The above is not to be considered an exhaustive 1 listing of applicable cleaning fluids, since those skilled in 2 the art will readily identify or develop additional or new 3 suitable cleaning fluids.
4 Any suitable source of cleaning fluid may be employed.

For example, in the case of cleaning gas, the cleaning fluid 6 source may be a commercial gas cylinder connected through 7 appropriate accessory equipment including, for example, a 8 pressure regulator, automatic shut-off valves and other safety 9 equipment, a flow measuring device and any other necessary or desirable components familiar to those skilled in the art. In 11 the alternative, the cleaning fluid source may be a reactor 12 situated adjacent the: water impound, such as a vessel for 13 admixing sulfuric acid and sodium chloride and collecting the 14 hydrogen chloride gas generated by the resulting reaction. An illustrative source of cleaning liquid is a tank of liquid 16 formic acid or liquid :hydrochloride acid connected with a pump 17 to transfer the liquid acid from the tank into the cleaning 18 fluid channel. Yet another example is the combination of a 19 commercial gas cylinder containing acid gas and connected through appropriate ac<:essory equipment including, for example, 21 a pressure regulator, shut-off valve and conduit with a vessel 22 for mixing the gas with water to form liquid acid, from which 23 vessel the liquid is pumped into the cleaning fluid channel.

24 Cleaning fluid may also be formed by reaction of components within the piping system or diffusers. For example, one 26 component could be sent to the diffuser plenums via the 27 aeration gas channel 'and the other via the cleaning gas 28 channel. Alternatively, the components could be supplied 29 separately, but in sequence, through the same channel.

Cleaning fluid channel parts are preferably constructed of 31 materials resistant 'to the cleaning fluid to be used, and are 32 preferably of acid-resistant materials. Particularly preferred 33 for this purpose are conduits formed of synthetic polymeric 1 material including both rigid and non-rigid resinous materials 2 and elastomers. PVC has been demonstrated to have the 3 requisite desired acid resistance, but persons skilled in the 4 art will readily supply alternative materials.
It will seldom be necessary for cleaning fluid channels to 6 handle the same volumes of fluid as the aeration gas channels.
7 Thus, the internal cross-sectional areas of the cleaning fluid 8 channels may be substantially smaller than the corresponding 9 areas of the aeration gas channels. This affords opportunities to mount the conduits of the cleaning fluid channels either 11 within or without the aeration gas channel conduits, as will be 12 shown in greater detail below. Whether the cleaning fluid 13 conduits are mounted inside or outside the aeration gas 14 conduits, it is preferred that the cleaning fluid conduits co-extend with substantially the entire portion of the length of 16 the aeration gas conduits which support the diffusers.
17 Cleaning fluid from a suitable source is conducted by the 18 cleaning fluid channel along a flow path separated from that of 19 the aeration gas, so that the cleaning fluid may be introduced substantially direct to the diffusers. Thus, for example, the 21 cleaning fluid channel may discharge the cleaning fluid at 22 (including in, or near) the diffuser aeration gas inlet.
23 Especially with gaseous cleaning fluid, if it is intended 24 that aeration gas will always be flowing at a substantial rate during introduction of cleaning gas, the aeration gas channel 26 can be arranged to discharge the cleaning gas into the aeration 27 gas channel a short distance upstream of the diffuser aeration 28 gas inlets or in the diffuser aeration gas inlets, upstream of 29 any flow regulator which may be present. With the cleaning fluid channel gas discharge being positioned closely adjacent 31 to the diffuser aeration gas inlet, the aeration gas flow will 32 readily sweep the cleaning gas into the diffuser, thus 1 accomplishing substantially direct delivery of the cleaning 2 fluid to the diffuser,.
3 However, for both gaseous and liquid cleaning fluids, 4 whether or not aeration gas will be flowing during application of cleaning fluid, it is preferred that the cleaning gas 6 channel have its discharge means arranged to release cleaning 7 fluid substantially entirely within the diffusers. This causes 8 initial contact of aeration gas and cleaning fluid to occur 9 within the diffusers. More preferably, such release and l0 initial contact will take place downstream of any aeration gas 11 flow regulating means which may be present in the diffusers, 12 and still more preferably in the diffuser plenums, when such 13 are provided.
14 New variations on prior in-situ cleaning processes are made possible by the present invention. Several non-limiting 16 examples, which we respectively refer to as direct delivery gas 17 cleaning, direct delivery liquid cleaning and direct delivery 18 liquid cleaning with continuing aeration gas flow, are 19 described below.
In direct delivery gas cleaning, cleaning fluid is 21 conveyed directly to the diffusers rather than through the 22 aeration gas channel, but the process may in other respects be 23 conducted in a manner quite similar to the teachings of Schmit 24 et al U.S. Patent 4,,382,867. For example, the equipment utilized in direct delivery gas cleaning may be and preferably 26 is largely similar to that disclosed in the Schmit et al patent 27 except for the limited modifications disclosed herein. These 28 modifications require the use of extra conduit for the cleaning 29 fluid, but permit a wider choice of materials for the aeration gas channel, make it more convenient or less costly to install 31 gas cleaning in an existing aeration plant with stainless steel 32 or other metal aeration gas channels and affords greater 1 versatility than previous gas cleaning systems, in that the 2 modified equipment can. be made suitable to perform both gas and 3 liquid cleaning, giving the plant operator a correspondingly 4 wider choice of maintEanance options.
It is believed that direct delivery gas cleaning, as well 6 as the direct delivery liquid cleaning to be described below, 7 will perform to best advantage against what the above-8 identified EPA 1989 Fine Pore Aeration Systems Design Manual 9 refers to as Type 1 fouling. As shown by page 41 of the Manual, Type 1 fouling comprises inorganic materials which clog 11 the diffuser pores at the influent and/or effluent surfaces of 12 the elements, while Type 2 fouling comprises mainly organic 13 material such as bio-films which form on the effluent surfaces.

14 In the aeration of mixed liquors in the activated sludge process, both types of fouling can appear on the same 16 diffusers.

17 For reasons explained in the Manual, it appears that when 18 fouling is predominantly of Type 1, the earliest stages of 19 fouling may actually improve uniformity of distribution of air discharge over the :surfaces of individual elements, with 21 consequent improvement of OTE (oxygen transfer efficiency).

22 Thus, when applying the present invention in this situation, 23 the best results may :be obtained by deferring cleaning until 24 the increased power costs resulting from increased DWP have overcome the benefits. of such OTE improvement. Thus, for 26 example, cleaning may be conducted intermittently and deferred 27 until after DWP had increased by at least about 5 inches of 28 water gauge above the diffusion element base condition, e.g.

29 its DWP when new or last thoroughly cleaned. However, neither deferring cleaning in this manner or the attainment of OTE

31 improvement are required in the practice of the present 32 invention. It is also preferred that cleaning be conducted in 33 such a way or with such frequency to restrict the increase of ~~a~9~~

1 DWP over the base condition, if any, to about 15 inches of 2 water gauge or less. However, the invention is not limited to 3 operations within thisc 15 inch range.

4 It does not appear that the bio-films of Type 2 have a beneficial effect on OTE, and may be deleterious to OTE from 6 their onset. Thus, it is preferred not to delay cleaning when 7 dealing with foulants predominantly of Type 2. Because such 8 foulants appear to reduce the surface tension of the bubbles at 9 the element effluent surfaces, such foulants may actually reduce DWP to some extent or for some period of time. In such 11 circumstances, BRV may be a more dependable measure of fouling, 12 and it may be best to clean with sufficient frequency to 13 prevent any substantial accretion of bio-films on the element 14 surfaces. This may therefore involve cleaning when the DWP of the elements has decreased, remained at zero or increased to a 16 value in the range of up to about 5 inches of water gauge.

17 Direct delivery gas cleaning may be performed with 18 proportions of aeration gas and cleaning gas similar to those 19 used in the Schmit et al patent, with or without added water vapor. This includes 'the use of the Schmit et al teachings of 21 enhancing aeration gas flow during application of cleaning gas.

22 For example, if the normal or usual aeration gas flow for a 23 given season and time of day were about 3 SCFM per square foot 24 of diffuser gas discharge area, the aeration gas rate might be increased to 4 or more SCFM per square foot during application 26 of cleaning gas. However, it is also contemplated that the 27 rate of aeration gas flow could be reduced substantially below 28 3 SCFM per square foot during application of cleaning gas, such 29 as to afford increased contact time between the cleaning gas and the foulants in the diffusion element.

31 At least about 0.05 and more preferably at least about 0.1 32 pounds of cleaning gas per diffuser will suffice for cleaning ~'~~~~9~J
1 diffusers. It appears that the present invention can in 2 certain circumstances be practiced with smaller quantities of 3 cleaning fluid would be required by the method taught in the 4 above-mentioned 1983 Schmit et al gas cleaning patent. In 5 certain plants and under certain climatic conditions, aeration 6 gas channels may contain substantial amounts of liquid water 7 condensate, which may absorb the initial portion of the flow of 8 cleaning gas and hold it in solution while subsequent portions 9 of the cleaning gas flow continue to the diffusers and clean 1o the elements. After the introduction of cleaning gas into the 11 aeration gas channel :is discontinued, the dissolved acid gas 12 will be stripped from the condensate and will pass through the 13 diffusers, but will afford little benefit if the diffusers are 14 already substantially~~lean. Direct delivery of cleaning fluid 15 to the diffusers avoids the hold-up of cleaning gas in 16 condensate in the aeration gas channel, so that all of the 17 cleaning gas may be applied to the elements during the cleaning 18 operation.

19 There is another way of saving cleaning gas in direct 20 delivery gas cleaning which does not depend upon the presence 21 of condensate in the aeration gas channel. When gas cleaning 22 according to the Schmit: et al patent is substantially complete, 23 the aeration gas channel may still contain cleaning gas. If 24 the diffusion elements are substantially clean at this point, 25 the subsequent passage' of this residual cleaning gas through 26 the diffusers will be of little or no significant benefit.

27 This form of consumption of cleaning gas does not occur in the 28 direct delivery gas cleaning method.

29 Although direct dE~livery gas cleaning may require somewhat 30 less cleaning gas than is recommended in the Schmit et al 31 patent, determining the optimum proportions to use in the 32 direct delivery method should not be difficult. Persons 33 skilled in the art should be able to determine the optimum 1 proportions through rEaasonable experimentation, starting with 2 the recommendations contained in the Schmit et al patent.
3 The flow of cleaning gas from the diffusers into the 4 aeration gas channel is not necessarily excluded from direct delivery gas cleaning, considered in its broadest context. In 6 fact, the cleaning f:Luid concentration in the aeration gas 7 channel may be significant if there is little or no aeration 8 gas flow during application of cleaning gas and there is no 9 effective barrier against the flow of cleaning gas at the diffuser element inlet, such as if there were no one-way valves 11 at the aeration gas in:Lets of the diffusers or if the diffusers 12 had flow regulators with particularly large orifices.
13 However, it is preferred to conduct direct delivery gas 14 cleaning in such a way that the concentration of cleaning gas in the aeration gas channel is substantially less than in the 16 practice of the Schm~~t et al patent. Thus, in the direct 17 delivery method, the cleaning gas concentration in the aeration 18 gas channel is preferably substantially less than the cleaning 19 gas concentration in the diffusers or less than in the diffuser plenums, where such are employed. Thus, it is preferred to 21 substantially restrict the flow of cleaning fluid into the 22 aeration gas channel, such as by maintaining a sufficient 23 amount of flow of aeration gas from the aeration gas channel 24 into the diffuser, or by employing an aeration gas flow regulator with a sufficiently small orifice to substantially 26 restrict flow of cleaning gas from the diffuser into the 27 aeration gas channel.

28 It is particularly preferred to substantially exclude 29 cleaning gas from the: aeration gas channel when practicing direct delivery gas cleaning. This can be accomplished by a 31 substantial flow of aeration gas into the diffuser, which will 32 include any amount of flow of aeration gas that is sufficient 1 to substantially exclude cleaning fluid from the aeration gas 2 channel which may include either enhanced or reduced flow of 3 aeration gas as described above. Substantial exclusion of 4 cleaning gas from the aeration gas channel may also be accomplished with various devices. Examples include one-way 6 valves at the aeration gas inlets to the diffusers and flow 7 regulators with back-flow preventing means.
8 According to one embodiment of direct delivery gas 9 cleaning, a cleaning liquid can be used to release vapors that act as a cleaning gas. This embodiment employs a plenum having 11 a liquid reservoir which can hold one or more pools or other 12 accumulations of a liquid having in solution an acid gas or 13 other cleaning agent which can be stripped from the liquid by 14 contact between the liquid and a flow of aeration gas.
This embodiment is performed in apparatus in which the 16 plenums have aeration gas inlets positioned for bringing about 17 intimate contact between aeration gas and the above-mentioned 18 liquid. This may be accomplished for example in diffusers 19 having plenums, including those with flow regulating means having their orifices above the crests of an arcuate plenum 21 bottom wall, or at substantially the same elevation as the 22 crests of the arcuate bottom wall or at a low point in the 23 plenum.
24 Liquid flows ini=o the plenum via the cleaning fluid channel provided by the present invention, either in a 26 continuing or intermitaent flow, including one shot or plural 27 shot additions to provide the pool or accumulation mentioned 28 above. The liquid leveal in this accumulation of cleaning fluid 29 is maintained sufficient for bringing about mixing or other contact between the liquid and aeration gas. This may for 31 example be accomplished by maintaining the liquid level at or 32 above the elevation of the aeration gas inlet or inlets, or by 1 maintaining such levesl below the aeration gas inlets and 2 employing suitable deflector means to bring about the desired 3 contact.
4 Although the liquid level may be intermittently high enough to fill the plenum, the plenum is preferably no more 6 than partly full during a sufficient portion of the cleaning 7 operation to accomplish measurable gas cleaning, e.g., to 8 remove about 20 percent or more of the foulant present in 9 (including on) the diffuser. More preferably, the plenum is no more than partly full during most of the cleaning operation.
11 Most preferably, the level of the liquid is below the element 12 influent surface at substantially all times.
13 A continuing flow of aeration gas is applied during 14 cleaning. This flow aspirates or strips vapors from the reservoir of cleaning liquid. These vapors pass through the 16 diffusion elements and clean them. While this continuing flow 17 of aeration gas may be interrupted for periods of quiescent 18 contact of cleaning :fluid with foulants, the aeration gas 19 preferably flows during the majority of, preferably during at least about 75% of, mare preferably during at least about 90%
21 of and most preferabl~,~ substantially throughout the cleaning 22 cycle.
23 In direct delivery liquid cleaning, as in direct delivery 24 gas cleaning, the cleaning fluid is transported direct to the diffusers without traversing substantial portions of the 26 aeration gas channel. In all other respects, direct delivery 27 liquid cleaning is similar to the "external mixture" method of 28 cleaning disclosed by Cummings, Jr. in U.S. Patent 5,051,913.
29 Direct delivery liquid cleaning may be conducted in equipment which is substantially the same as that disclosed by 31 Cummings except for the limited modifications taught herein.

~~o~~~~

1 While direct delivery liquid cleaning requires more conduit for 2 the cleaning fluid channel, direct delivery liquid cleaning 3 offers advantages over Cummings that are similar to the 4 advantages of direct delivery gas cleaning over the Schmit et al method.
6 Direct delivery liquid cleaning requires no more cleaning 7 liquid than is employed by Cummings and, for reasons set forth 8 above, less cleaning fluid should be sufficient since there is 9 no need to fill the aeration gas channel with cleaning liquid.
Persons skilled in the art will readily determine the optimum 11 proportions of liquid cleaning agent without undue 12 experimentation.
13 Flow of cleaning liquid from the diffusers into the 14 aeration gas channel i;s not necessarily excluded and there may be substantial amounts of cleaning liqsid in the aeration gas 16 channel during direct delivery liquid cleaning if no effective 17 barrier to such flow results from the design of the aeration 18 system. However, the amount of cleaning liquid admitted to the 19 aeration gas channel is preferably substantially less than would be present in such channel in the practice of the 21 Cummings, Jr. external mixture method.
22 Thus, the practice of direct delivery liquid cleaning is 23 not accompanied by filling the aeration gas channel full with 24 cleaning liquid. Preferably, the cleaning liquid flow into the aeration gas channel is substantially restricted by means at 26 the aeration gas inlets into the diffusers so that, on average, 27 the cleaning liquid falls no more than half of the air main 28 cross-section. This may for example be accomplished by 29 providing the diffusers with aeration gas flow regulators with small control orifice:. More preferably, cleaning liquid is 31 substantially excluded from the aeration gas channel by the 1 equipment, such as by a one-way valve at the diffuser aeration 2 gas inlets or by flow regulators with back-flow preventers.
3 As in the Cummings, Jr. process, the plenum and diffusion 4 element are preferably kept substantially full or flooded with liquid cleaning agent: during most of the cleaning period.

6 Direct delivery liquid cleaning can be practiced with or 7 without quiescent periods, provided their duration is not so 8 excessive as to seriously impair the microorganisms, if such 9 are employed in the process, or to unacceptably reduce plant output. Thus, it is possible to force fresh cleaning liquid 11 into the pores of the diffusion elements intermittently as 12 taught by Cummings, Jr. However, in direct delivery liquid 13 cleaning, the additional acid comes from the cleaning fluid 14 channel rather than from the aeration gas channel. The foregoing techniques can be interspersed with periods of 16 aeration gas flow, with or without bumping of the aeration gas 17 flow, affording an opportunity for alternately cleaning and 18 purging the elements. Bumping may for example include 19 increasing gas flow through the diffusers from its normal rate to a substantially increased rate (e. g. 200 - 300% increase) 21 for a limited period I;e.g. 15 - 30 minutes).

22 In general, direct delivery liquid cleaning with 23 continuing aeration gas flow includes filling the diffusers 24 with a liquid cleaning agent. While the diffusers are filled or "flooded" in this manner, a flow of aeration gas is caused 26 to pass through the diffusers and their respective elements.

27 This flow assists in conveying cleaning liquid into and through 28 the elements, agitating the cleaning liquid in the pores of the 29 elements and sweeping out of the pores spent liquid, dislodged foulant or both of then above.

31 Flooding the diffusers includes at least partly filling or 32 flooding the elements and filling the remaining parts of the 1 diffusers which are accessible to the liquid, including plenums 2 where such are provided. Flooding may be accomplished with a 3 constant flow of liquid from the cleaning fluid channel into 4 the diffusers. Such constant flow may be matched to the rate of discharge of cleaning liquid from the elements to maintain 6 the elements partly on completely filled, while the remaining 7 liquid-accessible portions of the diffusers remain flooded. If 8 the constant flow of liquid is not matched to the discharge of 9 cleaning liquid from the elements, such flow may for example be sufficient either to supply excess acid to the diffusers, 11 including their elements, or to initially flood the diffusers 12 and then supply a deficiency of liquid which will result in a 13 gradual reduction of t:he liquid level in the elements.

14 Instead of being constant, the flow of cleaning liquid which floods the diffusers may be intermittent or pulsating.

16 For example, such intermittent flow may be used to 17 intermittently flood the diffusers and their elements and to 18 intermittent lower the: liquid level below the element influent 19 surfaces. In this manner, a space may be intermittently provided between the surface of the liquid within the diffuser 21 and the element influent surface. Such lowering of the liquid 22 level, depending upon its duration and the rate of flow of 23 aeration gas, may or may not result in purging of the cleaning 24 liquid from the elements. In pulsating operation, there may for example be a flow of cleaning liquid for an extended 26 period, during which the flow occurs at a base rate for most of 27 the time in the period and during which the flow at base rate 28 is repetitively pulsed, i.e. there is flow at increasing, 29 increased, decreasing or decreased rate(s), for relatively short portions of the period.

31 The amount of acid used in a given cleaning cycle will be 32 sufficient to bring about significant cleaning of the elements, 33 e.g., at least about a 20% reduction in the BRV or DWP increase ~1~°~~9fl 1 attributable to fouling since the element was new or last 2 cleaned. When a constant flow of cleaning liquid is employed 3 as above described, the amount of liquid cleaning agent 4 required is expected to be greater than in direct delivery liquid cleaning. When an intermittent flow is employed, the 6 amount of cleaning liquid is expected to be less than in direct 7 liquid cleaning. In any event, it is anticipated that persons 8 skilled in the art will readily determine the amount of liquid 9 cleaning agent to be used without undue experimentation.

The continuing flow of aeration gas employed herein is 11 contrary to the teachings of Cunnings Jr. Although the present 12 embodiment of the invention allows for the possibility of 13 quiescent periods (pe:riods with no flow of aeration gas) as 14 taught by Cunnings Jr., characterization of the flow of the present embodiment as "continuing" signifies that the gas flow 16 is substantial in amount and/or time (duration) during 17 maintenance of flooded conditions in the diffusers.

18 The amount of aeration gas applied during flooding may be 19 expressed as a percentage of the amount of aeration gas which would have been applied while operating the aeration facility 21 at its "normal" aeration gas rate during the period of flooding 22 with cleaning liquid. For the "normal" rate, one may use 23 substantially that rate which would be applied in the aeration 24 facility, if the environmental, load and/or other factors that have been applied in establishing aeration gas rate for that 26 particular facility are applied in the same manner and to the 27 same extent that they have been applied in the recent plant 28 operating history (e.g. up to five years) to establish aeration 29 gas rate when cleaning was not occurring. However, if the data for establishing the rate as above described is not readily 31 available, or if the foregoing gas rate cannot readily be 32 determined for other reasons, one may use as the "normal" rate w .

1 the average aeration gas rate used for the four weeks 2 immediately preceding the cleaning operation.
3 Based on the normal rate as above-described, the 4 applicable percentages of normal aeration gas rate which may be applied in this embodiment of the invention include at least 6 about 20%, more preferably at least about 40%, still more 7 preferably at least about 60% and in some instances more than 8 80% . Using less than 7.00% or less than about 80% of the normal 9 amount may be beneficial in conserving acid and sufficient to perform one or more of the targeted functions described below.
11 Use of 100% of the normal amount is contemplated, and larger 12 amounts may be used if desired.
13 In practicing direct delivery liquid cleaning with 14 continuing aeration gas flow, the aeration gas is caused to flow during the majorii:y of the time the diffusers are flooded.
16 Preferably, the flow continues for at least about 60% of the 17 time, more preferably .at least about 75% of the time and still 18 more preferably more than about 90% of the time. Most 19 preferably, gas flows substantially all of the time during which the diffusers .are flooded. Moreover, it should be 21 understood that the invention includes partial or complete 22 replacement of the aeration gas, during cleaning, with any 23 other gas that is compatible with the system parts and cleaning 24 operation.
The above flow .amounts and durations may be used in 26 combination with various aeration gas flow rates. More 27 particularly, the aeration gas flow rate may be established or 28 controlled in relation to or in conjunction with any of the 29 above amounts or time options. Thus, the rate employed may be a rate which is normal or typical for the plant, given the 31 prevailing load, environmental and other factors. On the other 32 hand, an enhanced or greater than normal rate of flow may be 1 employed, for example to produce a more intense agitation of 2 the cleaning liquid in foulant, to maintain a substantial 3 amount of aeration gas discharged into the water while 4 restricting the percentage of time during which aeration gas is discharged, or for any other reason or combination of reasons.
6 Moreover, a reduced oz- less than normal aeration gas rate may 7 be employed for conserving liquid cleaning agent or for any 8 other purpose.
9 In accordance with this embodiment of the invention, the amount and/or time o:E flow of aeration gas is selected in il conjunction with the aeration gas rate for promoting or 12 improving any one or combination of the following targeted 13 performance factors, as compared to the levels of such factors 14 attained in the absence of aeration gas flow. Among these factors is cleaning pE~rformance. It includes the rate and/or 16 degree of completeness of cleaning. These are manifested 17 respectively by the time required to reduce and by the extent 18 of reduction of any B:RV or DWP increase which is observed in 19 the elements and is attributable to fouling of the elements since they were new or were last cleaned. The amount and/or 21 time of aeration gas flow may also be selected to promote or 22 improve the survival or condition of bacteria, if such are used 23 in the aeration process. Also, if the invention is being 24 employed as part of an activated sludge wastewater treatment process, the selection may be based on promotion or improvement 26 of the proportion of mixed liquor solids kept in suspension, 27 thereby substantially reducing or eliminating difficulties 28 associated with sludge: settling on diffusers, on the bottom of 29 the water impound or both.

DETAILED DESCRIPTION OF THE DRAWINGS
31 FIGS. 1-12 disclose several of many possible embodiments 32 of apparatus for aeration of wastewater with an aeration gas in 3 3 accordance with the invention, as wel l as a related process and 1 methods of assembly. 'the preferred apparatus embodiments each 2 include a water impound, an aeration gas channel, fine pore 3 diffusers and a cleaning fluid channel in an aeration system.
4 As shown in the drawings, it is preferred that the aeration gas channels include substantially horizontally disposed aeration 6 , gas conduits which will be submerged in the wastewater when the 7 diffusers are in normal operation, and that the cleaning fluid 8 conduits run along the outsides (FIGS. 1-5) or the insides 9 (FIGS. 6 and 7-12) of the horizontally disposed conduits to the plenums.
11 In the embodiment of FIGS. 1-5, the water impound is an 12 aeration tank 7. It :has wall means including a tank floor 9 13 with tank side wall :11 and tank end wall 13. The tank is 14 provided for the purpose of containing a body of water or other aqueous liquid which, in this case, is mixed liquor, a mixture 16 of wastewater and return sludge, which is to be aerated in an 17 activated sludge process.
18 Serving as a source of aeration gas comprising oxygen, 19 which in this instance is air from the atmosphere, compressor 15, valve 17b, and flow indicator 19a feed the air through an 21 attachment, such as coupling 16, into at least one aeration gas 22 channel. In this embodiment, there is an aeration gas channel 23 which includes a plurality of aeration gas conduits.
24 Conduits included in the aeration gas channel provide a first flow path to convey aeration gas to diffusers positioned 26 in the above-mentioned zone. The materials of which the 27 aeration gas conduits are fabricated is chosen with due regard 28 to their resistance to corrosion, weather, collapse and impact 29 and such other stresses as may be exerted thereon in fabrication, assembly and use. These conduits are preferably 31 fabricated of synthetic resinous material, such as ABS
32 (acrylonitrile-butadiene-styrene) or preferably PVC

2~a~~~~

1 (polyvinylchloride), and may for example include one or more 2 air mains, downcomers, manifold conduits and distributor 3 conduits.
4 For example, in this embodiment, air main 21 is generally supported above the level of mixed liquor in tank 7, and feeds 6 air into an air downcomer pipe 23 extending vertically from air 7 main 21 to feed horizontally disposed air manifold conduit 25 8 supported substantially horizontally a short distance above 9 tank floor 9. One end. of aeration gas manifold conduit 25 is connected with, indirectly, the attachment, e.g., coupling 16, 11 by which the aeration gas channel is connected with the 12 aeration gas source.
13 Parallel rows of air distributor conduits, in this case 14 pipes 27, are also supported substantially horizontally a short distance above the tank floor 9. At least portions of these 16 conduits extend generally horizontally within a zone comprising 17 the lower half and bottom area of tank 7 and will be submerged 18 in the wastewater when the tank is in normal operation.
19 Distributor conduits 27 are fed by air manifold pipe 25, and each represents a branch of the aeration gas channel, for 21 feeding a given set of diffusers 39 in a manner to be disclosed 22 in greater detail below. The spacing, in a horizontal plane, 23 of air distributor conduits 27 and diffusers 39 is determined 24 on the basis of criteria known to persons skilled in the art.
A source of cle<~ning fluid, which in this embodiment 26 includes a pressurized tank 28, as well as a valve 17a and a 27 flow indicator 19b, feeds cleaning fluid through an inlet, such 28 as a coupling 30, into one or more cleaning fluid channels.
29 Tank 28 may for example contain HC1 gas or liquid hydrochloric acid or any other cleaning fluid that is aggressive toward 31 organic or inorganic foulants. In the present embodiment there 1 is a cleaning fluid channel which includes a plurality of 2 cleaning fluid conduits.
3 The conduits of the cleaning fluid channel provide a 4 second flow path, a portion of which connects with and conveys cleaning fluid to the diffusers positioned in the above-6 mentioned zone. The materials of which the cleaning fluid 7 conduits are fabricated are chosen with due regard to their 8 resistance to corrosion, weather, collapse and impact and such 9 other stresses as may be exerted thereon in fabrication, assembly and use. They are preferably fabricated of synthetic 11 resins, such as PE (polyethylene), PP (polypropylene) or 12 preferably PVC (polyvi:nylchloride), and may for example include 13 one or more fluid mains, downcomer pipes, manifold conduits and 14 distributor conduits.
By way of illustration, fluid main 29 is generally 16 supported above the level of liquid in the tank 7, and feeds 17 into fluid downcomer pipe 31 extending vertically from fluid 18 main 29 to a fluid manifold pipe 33. One end of cleaning fluid 19 manifold pipe 25 is indirectly connected with the inlet, coupling 30, by which the cleaning fluid channel is connected 21 with the cleaning fluid source.
22 There is no requirement that any portion of the conduits 23 defining the cleaning fluid channel must extend horizontally.
24 However, it is preferred that portions of these conduits do extend generally horizontally within the above-mentioned zone 26 of tank 7, so that they are submerged in the wastewater when 27 the tank is in normal operation. Thus, pipe 33 is preferably 28 supported substantially horizontally a short distance above 29 tank floor 9. Parallel rows of fluid distributor pipes 35, also preferably supported substantially horizontally a short 31 distance above the tank floor 9, are fed by fluid manifold pipe 32 33 through fluid manifold valve 34. Accordingly, in this 1 embodiment, fluid maim 29, fluid downcomer 31, fluid manifold 2 33 and fluid distributors 35 respectively run substantially 3 parallel to the air main 21, air downcomer 23, air manifold 25 4 and air distributors 27.
FIGS. 2 and 5 are respectively views in perspective and 6 elevation of a portion of one of the air distributors 27, to 7 which are attached diffusers 39 and fluid distributor tubing 8 35. Fluid distributor tubing 35 is bound to the exterior of 9 air distributor 27 by plastic strip rachet ties 37 and is routed past a plurality of diffusers 39 to feed cleaning fluid 11 to them in a manner to be described in greater detail below.

12 As shown in FIGS. 2, 4 and 5, the cleaning fluid channel 13 preferably includes a plurality of cleaning fluid conduit 14 segments. For example, the distributor tubing 35 may be divided into segments 35a, 35b, 35c and 35d, which are 16 positioned for passing cleaning fluid from a position adjacent 17 one of said diffusers :39 to a position adjacent another of said 18 diffusers. It is not required, but it is preferred, that these 19 segments extend generally parallel to generally horizontally extending portions of the aeration gas conduits within the 21 aforementioned zone, as shown in the figures. Although it is 22 not essential that they do so, it is also preferred that these 23 cleaning fluid conduit segments extend along the outside of and 24 closely adjacent said generally horizontally extending portions of said aeration gas conduits within said zone, which is also 26 shown in these drawings. Thus, this embodiment of the 27 apparatus is capable of performing a process in which at least 28 part of the portion of the second flow path, including that 29 part which connects with the diffusers, is located outside a horizontally disposed portion of the first flow path.

31 The tubing 35 of FIGS. 2 through 5 may, as an alternative 32 to what is shown, be a single piece of tubing, and it may be ~~0~~~~

1 pierced by fluid taps at intervals along its length which 2 correspond to the separation of adjacent diffusers. If such 3 taps are connected with the interiors of the diffusers, the 4 tubing may transmit fluid to the diffusers. Whether tubing 35 is in a single piece ar is divided into segments, FIG. 2 will 6 be capable of performing a process in which at least part of a 7 first or aeration gas flow path is in a first conduit, e.g., 8 the conduit 27, and :in which at least part of a second or 9 cleaning fluid flow path is in a second conduit, e.g., the l0 tubing 35, whether the second conduit be in one piece or in 11 several segments, such second conduit being bound to the 12 exterior of said first: conduit.
13 Diffusers 39 o:f FIG. 2 are representative of a 14 multiplicity of fine pore diffusers included in this preferred embodiment. As illustrated in FIG. 1, the multiple diffusers 16 may be distributed in arrays familiar to those skilled in the 17 art and arranged in regular and varying patterns to achieve the 18 desired distribution of air in the tank. Such arrays may for 19 example include sets of diffusers, each set being a series of diffusers supported on a common aeration gas supply conduit.
21 As shown in FIGS. 2 and 3, the diffusers are mounted at 22 longitudinally spaced intervals along the lengths of, and in 23 communication with the interiors of, the generally horizontal 24 portions of said aeration gas conduits.
The diffusers optionally but preferably include plenums.
26 FIG. 3 is a transverse, vertical cross-section through one of 27 the diffusers 39 in FI:G. 2, taken on section line 3-3 of FIG.
28 2, and shows the interior of the diffuser, including its 29 plenum. Plenum 43 of this preferred diffuser includes surrounding wall means comprising a lower plenum wall 45 and 31 side wall 46. Side wal_1 46 corresponds in shape with a portion 32 of a cone and is preferably molded or cast integrally with 33 lower wall 45. All or at least a substantial portion of lower 1 wall 45 is circular in transverse cross section and much if not 2 all of its under-surface conforms to, and is welded by ultrasonic-3 or preferably adhesive- welding to, the air distributor pipe 4 outer, upper surface 9.7.
The upper edge of plenum side wall 46 includes means, 6 known to those skilled in the art, for supporting a diffusion 7 element 48. Particularly preferred arrangements for sealing 8 and retaining such diffusion element 48 in gas-tight 9 relationship with the interior of the plenum are described in Schmit et al U.S. Patent 4,382,867. In this embodiment, the 11 diffusion element is an MPDE (multi-pore diffusion element), 12 but any fine pore diffusion element may be employed.
13 One or more gas passages provide connections between the 14 first or aeration gas flow path and each diffuser. Through such passages, aeration gas may be introduced into the 16 diffusers, including introduction of the gas into the diffuser 17 plenums where such are employed, for causing discharge of the 18 gas through the diffusion elements, thereby aerating the 19 wastewater. The diffusion elements of the fine pore diffusers are generally subject to accumulation of foulants in and/or on 21 the elements during such discharge, including organic or 22 inorganic foulants and mixtures thereof.
23 The passages) through which aeration gas passes from the 24 first or aeration gas flow path into the diffusers may be relatively large or small, with or without the ability to 26 perform gas regulation and/or other functions. It is preferred 27 that the flow cross-section of the passages) is selected to 28 provide flow regulation, and the passages) may be one or more 29 simple flow regulating orifices or parts of more complex flow regulation devices.

1 The flow regulating passages) may be located at a 2 physical interface between an aeration gas channel conduit and 3 the body of the diffuser or, if connected with such interface 4 by an extension duct that is external or internal relative to the diffuser, may be located upstream or downstream of such 6 interface. In the present preferred embodiment, aeration gas 7 passages are provided which are part of a flow regulator, and 8 the passages are located downstream of the flow path-diffuser 9 interface. Thus, in this embodiment, air distributor pipe 27 has air outlet opening 41 in its top center line to feed air 11 into plenum 43 through an air opening 49 in the lower plenum 12 wall 45. Openings 41 and 49 and a small upstanding boss 51 on 13 the lower plenum wall 45 seat a sleeve mount 55 for the air 14 flow regulator 53 having a gas discharge passage 57 downstream of the flow path-diffuser interface and within the plenum 43.

16 One or a plurality of fluid pathways provide connections 17 between the second or cleaning fluid flow path and each 18 diffuser. Through such pathways, cleaning fluid may be 19 introduced into the diffusers, including introduction into the diffuser plenums where such are employed, for causing discharge 21 of cleaning fluid through the diffusion elements, thereby 22 cleaning the elements.

23 Like the above-mentioned passages for the aeration gas, 24 the pathways) through which cleaning fluid passes from the second or cleaning fluid flow path into the diffusers may be 26 relatively large or small, with or without the ability to 27 perform gas regulation and/or other functions. However, it is 28 preferred that the flow cross-section of these pathways) 29 should be established to provide flow regulation, and the pathways) may therefore be one or more simple flow regulating 31 orifices or parts of more complex flow regulation devices.

32 Moreover, as with the aeration gas flow regulators, the 33 cleaning fluid flow regulating pathways) may be located at a 57 _ 2109990 physical interface between a cleaning fluid channel conduit and the body of the diffuser or, if connected with such interface by an exten~~ion duct that is external or internal relative to the difi=user, may be located upstream or, preferably, downstream of such interface.
Thus, as shown in the enlarged portion of FIG. 3A, the plenum side walls 46 have fluid inlet openings 59 into which are welded the base legs 63 of tee connectors 61 so that the outlet openings 65 of the base legs face the interior of the plenum 43. As shown in the enlarged portion of FIG. 3 a;~ well as in FIGS. 4 and 5, fluid distributor tubing segments, such as segments 35b and 35c (see segments 35b and 35c of Figs. 4 and 5), fit over the remaining legs defined by the body 67 of each tee connector, and are hE:ld in place by worm gear clamps 69 (see Fig. 5). Thu;~, in this embodiment, the outlet openings 65 of base legs 63 of tee connectors 61, located within the plenums 43, are the pathways through which the tubings 35 feed fluid to diffusers 39.
The present embodiment lends itself to fabrication techniques in which the cleaning fluid channel comprises conduit and plural tee connectors positioned at longitudinally spaced intervals along the conduit with their base legs projecting laterally from the conduit. In such methods the plenums have walls with holes that are spaced apart by substantially similar intervals and extend from the interiors of the plenums to the exteriors thereof, outside said aeration gas conduit, for receiving the base legs of the tee connectors. This makes it possible to secure a cleaning fluid channel portion to an aeration gas channel portion by securing said tee connector base legs in communication with said holes.
FIG. 6 shows an additional embodiment of the invention which is similar to 'that of FIGS. 1-5, except that the cleaning fluid channe7_ is mounted within the aeration gas channel. In - 58 _ 2109990 this embodiment, the base leg 63 of the tee connector 125 is welded in openings 127 and 129 through the air distribution pipe 27 and the lower plenum wall 45 so that the cleaning fluid di;~charge opening 65 faces the interior of the plenum 43. As in the previous embodiment, tubing 35 fits over the remaining legs defined by the tee connector body 67, being held in place by clamps 69 (see Fig. 5) or any other suitable means. Thus, this embodiment of the apparatus is capable of performing a process in which at least part of the portion of the second flow path, including that part which connects with the diffusers, is located inside a horizontally disposed portion of the first flow path.
Consideration of the embodiments of FIGS. 1-5 and 6 will show that the clE:aning fluid conduit segments 35a-35d (see segments 35a-35d of Fig. 2) and the tee connectors 61 servicing the multiple diffusers 39 are examples of plural members, located within the above-described zone of tank 7, that respectively have substantially separate and substantially direct connections to plural diffusers, and define cleaning fluid flow paths which remain substantially separate from said aeration gas channel in those parts of said flow paths which extend from said inlet to said diffusers. Having been taught this principle of the invention, persons skilled in the art will readily develop other such members which will not necessarily be or include conduit segments and/or tee connectors as above described.
When conducting cleaning, especially under conditions in which a substantial flow of aeration gas is not maintained throughout. and cleaning is performed in diffusers having plenums, it is useful if the size of the aeration gas passages from the first flow path into the diffusers is established to maintain some degree of control over back-flow of cleaning fluid from the diffusers into the aeration gas channel. Under these same conditions, it is also advantageous if the size of 1 the cleaning fluid pathways from the second flow path into the 2 diffusers is selected to maintain some degree of control over 3 back-flow of cleaning fluid from the diffusers into the 4 aeration gas channel.
Therefore, whether there be flow regulation or not, it is 6 preferred that the aeration gas passages and/or the cleaning 7 fluid pathways be small enough in flow cross-section so that 8 they constitute retarding means for substantially retarding 9 flow of cleaning fluid from said plenums into said aeration gas channel and/or into said cleaning fluid channel. This is 11 illustrated by the embodiments of FIGS. 1-5 and 6. Optionally, 12 with or without flow regulation, the passages and/or the 13 pathways may be equipped with one-way valve means positioned 14 for substantially preventing flow of cleaning fluid in the reverse direction from said plenums into said aeration gas 16 channel and/or into said cleaning fluid channel. However, this 17 option may be readily attained when the passages and/or 18 pathways are respectively equipped with aeration gas flow 19 regulating means and/o:r cleaning fluid flow regulating means to provide flows of aeration gas and/or cleaning fluid of 21 controlled flow rate from the aeration gas channel and/or from 22 the cleaning fluid channel in the direction of and into said 23 plenums. Such aeratian gas flow regulating means and/or such 24 cleaning fluid flow regulating means may for example include one-way valve means positioned for substantially preventing 26 flow of cleaning fluid from said plenums into said aeration gas 27 channel means and/or :into said cleaning fluid channel. When 28 the aeration gas flow regulating means and/or cleaning fluid 29 flow regulating means do include one-way valve means, as above described, it is preferred that the one-way valve means be 31 positioned within the plenums. This feature, among others, 32 will be illustrated with the embodiment of FIGS. 7-12.

FIGS. 7 through 12 show an alternate and even more preferred embodiment c>f the invention, having some features in common with the previous embodiments. FIG. 7 is a schematic diagram which includes a fragmentary view of a sewage aeration system that is similar to the one in FIG.
1 but has its cleaning fluid channels partially enclosed within the aeration gas channels. In this embodiment, as in the previous ones, aeration tank 7 has a tank floor 9 with tank side wall 11 and tank end wall 13 containing mixed liquor. Al:~o in common with the previous embodiments, a source of aeration gas (not shown) is connected with an aeration gas channel including air main 21, and a source of cleaning fluid (not shown) is connected with a cleaning fluid channel including cleaning fluid main 29.
As shown in FIG. 7, air main 21 is generally supported above the level of liquid in the tank 7, and feeds into an air downcomer pipe 23 extending vertically from air main 21 to a horizontally disposed air manifold pipe 25 supported substantially horizontally a short distance above tank floor 9. Parallel rows of air distributor pipes 130 are also supported substantially horizontally a short distance above the tank floor 9. Pipes 130 are connected to air manifold pipe 25 to :receive air therefrom through fixed couplings 26 and support sets of fine pore diffusers 39.
Cleaning fluid main 29, also shown in FIGS. 7 and 8, is generally supported above the level of liquid in the tank, and feeds into a fluid downcomer pipe 131 extending vertically from fluid main 29 to a horizontally disposed fluid manifold pipe 133 supported substantially horizontally a short distance above the tank floor 9 and also above air manifo7_d pipe 25. Fluid manifold pipe 133 has outlets through fluid branch line nipples 134, flexible tubes 135 and entry joints 137. At these joints, the cleaning fluid channel enters the aeration gas channel.
More particularly the cleaning fluid channel enters air ~:~~~3~U

1 distributor pipe 130 and, while providing a cleaning fluid flow 2 path separate from the aeration gas flow path, travels within 3 the pipe 130 to each of the multiple diffusers 39.
4 FIG. 9 is an exploded view of one of the entry joints 137 shown in FIG. 8. Flexible tube 135 is connected by a worm 6 screw clamp 139 to a. threaded barb fitting 141, which is 7 screwed into an external pipe bushing 143. Bushing 143 is 8 connected by nipple 149 through a center hole in circular plate 9 151 to an internal pipe bushing 153. Bushings 143 and 153 respectively abut against the upper and lower surfaces of plate 11 151, to which they are sealed by gaskets (not shown) or solvent 12 welding. Plate 151 fits into the mouth of a spigot sleeve 155 13 having male threads formed on the exterior of its mouth 14 portion, and is held i.n place by compatible female threads on the interior of retainer ring 145. An O-ring 147 compressed 16 between the retainer ring and plate 151 provides a watertight 17 seal between the plate and sleeve 155. This sleeve is welded 18 to a large nipple 132 formed on the air distributor pipe 130.

19 The internal pipe bushing 153 is screwed to the end of the fluid distributor pipe 157 within the air distributor pipe 130.

21 FIG. 10 shows the parts of FIG. 9 in their assembled form, 22 as well as a continuation of fluid distributor pipe 157 which 23 runs past the entrances to several diffusers 39 stationed along 24 air distributor pipe 1:30. After flexible tube 135 conducts the second or cleaning gas flow path to entry joint 137, where said 26 second path enters the first or aeration gas flow path by 27 penetrating air distributor pipe 130, the second path maintains 28 its separate identity by running through fluid distributor pipe 29 157 within the air distributor pipe 130. Pipes 130 and 157 are connected to each of the plenums 161 of diffusers 39 in a 31 manner shown in greater detail in FIG. 11.

1 FIG. 11 is an exploded and partially cut-away portion of 2 FIG. 10. It shows a connection between the fluid distributor 3 pipe 157 and the plenum 161 and a connection between the gas 4 distributor pipe 130 and the plenum 161. Such connections are replicated at each of the multiple plenums in the apparatus.
6 Each plenum 161 is bonded to gas distributor pipe 130 7 through an elastomer gasket 160 which forms a seal between 8 them. This seal includes an adhesive bond between the gasket 9 and the crown of the pipe and a further bond between the gasket and the plenum. In the figure, the crown of the pipe has been 11 removed to expose the interior of pipe 130.
12 Through pipe 130 runs fluid distributor pipe 157, and it 13 includes a plurality of pipe segments interspersed with plural 14 tee joints 158 at longitudinally spaced intervals along the length of pipe 157. The longitudinal axes of the base legs 159 16 of these connectors are parallel to one another and project 17 laterally from pipe 157.
18 A series of apertures 162 provides communication between 19 the interior of the gas distributor pipe 130 and the interiors of plenums 161. This .is accomplished by providing openings in 21 the crown of pipe 130, in the gaskets 130 and in the bottom 22 walls of plenums 161 which are in registry with one another.
23 These apertures are spaced apart along the length of pipe 130 24 at longitudinal intervals identical to those which separate tee joint base legs 159 and are of sufficient diameter for 26 insertion of these base legs.
27 Tee joint base :legs 159 have threaded portions which 28 extend upward through apertures 162 into the plenums 161, while 29 also passing through retaining blocks 163. In the assembled part, the base legs 159 are firmly held in place in apertures 31 162 and the blocks 163 are drawn tight against the lower plenum 1 wall 172 by split washers 165 and nuts 167 applied to the 2 threaded portions of base legs 159. Several turns of the 3 threads on base legs 159 project above nuts 167. To these 4 turns, with the aid of internally threaded retaining caps 171, are secured elastomer duck bill flow regulators 169, which also 6 constitute check valves.

7 The airways 174 from gas distributor pipe 130 into the 8 plenums 161 are offset from the crown of the pipe. These 9 airways comprise openings in upper portions of the walls of l0 pipe 130 which are within the "foot-prints" of the plenum 11 bottom walls 172, as well as registrated openings in the 12 gaskets 160 and in the plenum bottom walls themselves.

13 Threaded inserts 173 are solvent welded into the airways 174, 14 and elastomer duck bill flow regulators 175 with check valves are secured to the inserts 173 by internally threaded retaining 16 caps 177.

17 Subassemblies corresponding to the apparatus shown in 18 FIGS. 9-11 may be prefabricated in a mass production facility 19 and shipped to sites at which aeration plants are to be constructed. There the subassemblies may be united with other 21 components of the aeration gas channel and cleaning fluid 22 channel, such as those shown in FIGS. 7 and 8. In constructing 23 such a plant, it will normally be desired to considerably 24 extend the reach of the air distribution conduits to increase the number of diffusers and the floor area over which aeration 26 gas may be distributed, especially in large tanks. For this 27 purpose, subassemblies that are similar or modified in nature 28 as compared to that of FIG. 10 may be connected with one other 29 end to end in series, as will be described in connection with FIG. 12.

31 FIG. 12 shows a joint connecting two subassembly units 166 32 and 168 end to end in series, and it will be appreciated that 1 three or more subassemblies may be connected in series with 2 similar joints. Unit 166 has a fluid distributor pipe 157 3 running within an air distributor pipe 130, and unit 166 is 4 identical to the subassembly of FIG. 10 except that its pipe 157 has a free end 170 somewhat longer than free end 164 of 6 FIG. 10. Similarly, unit 168 has a fluid distributor pipe 178 7 running within an air distributor pipe 132. In other respects, 8 the construction of unit 168 is like that of unit 166 except 9 that coupling 26, fleaxible tubing 135, nipple 156 and the remainder of entry joint 137 are omitted.
11 Fluid distributor pipe 178 of unit 168 has at one of its 12 ends, i.e., the end shown in FIG. 12, an elongated free end 176 13 similar to free end :170 of pipe 157 of unit 166. If the 14 opposite end of unit 168 which is not shown in the figure will be connected to a third subassembly, then at that opposite end 16 of unit 168 its fluid distributor pipe 178 will have another 17 free end (not shown) similar to free end 176. A subassembly 18 which terminates a series of subassemblies will be similar to 19 subassembly 168, except that at its terminal end both the fluid distributor pipe 178 and air distributor pipe 132 will be 21 capped.
22 To provide access to adjacent free ends of gas distributor 23 pipes 157 and 178 for joining them in a manner to be described 24 below and to accommodate expansion and contraction of mated units 166 and 168 during use, the units have expansion barrels 26 179 and 180. These barrels, respectively bonded to the ends of 27 air distributor pipes :130 and 132, are of such inside diameter 28 to receive, in a close, sliding fit, the two ends of coupling 29 segment 185. Seals may be formed between the coupling segment ends and the barrels within which they are respectively 31 telescoped, with the aid of lubricated O-rings 181, 182 which 32 are held in place by threaded retainer rings 183, 184.

2~~99~'~
1 Anchor support 7.89, secured to the tank floor 9, is 2 provided to anchor and support air distributor coupling segment 3 185 and the units 166 and 168 which are attached to it, thus 4 securing the distribution system at a predetermined elevation 5 above the tank floor 9~. As is well known to those skilled in 6 the art, it is common for such supports to include height 7 adjusting means (only partially shown) to permit levelling of 8 the distribution system in compensation for irregularities in 9 tank floors. The inside diameter of the collar portion 195 of 10 the present anchor support is such as to receive the outside 11 diameter of coupling segment 185 in a close, sliding fit.

12 Thus, the coupling segment 185 can slide back and forth within 13 collar 195 and expansion barrels 179 and 180 when mating the 14 units to each other and to the support, before the retainer 15 rings 183, 184 are tightened.

16 During assembly of the joint of FIG. 12, coupling segment 17 185 is inserted lengthwise, moving from left to right through 18 collar 195, retainer ring 183, and O-ring 181, into expansion 19 barrel 179, until the right-hand end of the segment contacts 20 interior circumferential boss 190. This leaves free end 176 of 21 pipe 178 in unit 168 exposed. Then, flexible tubing 187 is fed 22 into coupling segment 185 with the first or leading end of the 23 tubing moving from left to right toward unit 166. The trailing 24 or second end of the tubing is then secured to free end 176 of 25 pipe 178 in unit 168, using worm screw clamp 192.
26 Now, coupling segment 185 is shifted longitudinally in 27 collar 195 in the opposite direction, from right to left, 28 moving the right-hand end of the segment out of expansion 29 barrel 179, O-ring 181, and retainer ring 183, while 30 introducing the segment left-hand end into retainer ring 184, 31 O-ring 182, and expansion barrel 179. Free end 170 of pipe 157 32 in unit 166 is now exposed, and is secured to the first end of 33 the tubing 187 with worm screw clamp 194. Tubing 187 has ~1~.~~~~~

1 longitudinal resilience for adapting to lengthwise movement of 2 pipes 157 and 178 toward and away from one another during 3 expansion and contraction of units 166 and 168.
4 Next, coupling segment 185 is shifted longitudinally in collar 195 in the original direction, from left to right, to 6 the central position shown in FIG. 12. Thus, the segment is 7 now within the retainer rings 183, 184, O-rings 181, 182, and 8 expansion barrels 179,. 180 of both the units 166, 168. Both 9 free ends 170, 176 of pipes 157,178, as well as tubing 187, are no longer exposed, being hidden within the joint as shown in 11 FIG. 12.

12 Water- and air- tight seals are now completed between the 13 air distributor coupling segment 185 and the expansion barrels 14 179 and 180 by tightening both threaded retainer rings 183, 184 against their respective lubricated O-rings 181, 182. With 16 controlled tightening of the retainer rings, resulting in only 17 moderate compression of the O-rings, it is possible to attain 18 the desired water- and air- tight seal and preserve the ability 19 of the coupling segment 185 and expansion barrels 179, 180 to undergo relative sliding movement when the units 166 and 168 21 expand and contract. Collar 195 may if desired be provided 22 with means (not shown) to prevent relative sliding movement 23 between the collar and coupling segment 185.

Aeration Gas - This is a gas, as defined herein, which 26 includes one or more oxygen-containing gases, such as pure 27 oxygen or air, and is able to deliver oxygen to a liquid medium 28 and/or to the contents of the liquid medium when distributed in 29 the liquid medium in the form of bubbles, but is less aggressive towards foulant deposits than a cleaning gas, as 31 defined herein.

1 Aqueous Medium -- An "aqueous medium" is water or a 2 combination of water .and one or more other liquid, solid or 3 gaseous components, said water or combination being liquid to 4 a sufficient extent to form gas bubbles therein when gas is discharged into the medium through a fine pore diffuser. Also, 6 at least one of the components of the medium, which may be one 7 or more foulant(s) and./or one of the other components of such 8 medium, is subject to beneficial change in a pre-determined 9 manner in response to discharge of a aeration gas therein. A

preferred category of such media is aqueous waste liquors, such 11 as for example, the mixed liquors treated in the activated 12 sludge process, refinery and brewery waste liquors, paper mill 13 white water, and the like.

14 Bubble Release Vacuum (BRV) - BRV is a test procedure useful for assessing the degree of uniformity of the effective 16 pore diameter of pores at the pore openings on the surfaces of 17 cleaned or fouled diffusion elements. BRV may be used as a 18 manufacturing control by measuring the BRVs of diffusion 19 elements a given type as they are produced, and comparing these BRVs with an established specification. New or thoroughly 21 cleaned diffusion elements of different types may be 22 characterized on the basis of their BRVs and may be compared 23 with one another by comparing their BRVs. The extent of 24 fouling of an element after a period of aeration service may be determined by taking BRV data on the element after such service 2 6 and comparing that data with BRV measurements taken on the same 27 elements or with BRV measurements taken on other comparable new 28 or thoroughly cleaned elements.

29 The test procedure measures the vacuum, which may be conveniently expressed in inches of water guage, that is 31 required to emit bubbles at a given flux from a localized area, 32 encompassed within the boundaries of a test probe held against 33 the surface of a thoroughly wetted element. In addition to a 1 vacuum source, the test apparatus also includes a manometer to 2 measure the vacuum, and a rotameter to measure the flux.
3 The value of the test results is enhanced by making and 4 averaging several measurements, preferably a statistically number of measurements, on each element tested. Further 6 enhancement is gained by making such tests at locations which 7 have been selected according to a predetermined plan to 8 distribute the measurement locations widely over the element 9 gas discharge surface. Further description of the technique may be found on pages 275-278 of the above-identified EPA
11 Design Manual.
12 Cleaning - Cleaning, a process applicable to the diffusion 13 elements of fine pore diffusers, includes at least partially or 14 wholly preventing, retarding, removing or beneficially modifying foulant deposits or increasing the available aeration 16 discharge surface of t:he elements, with the aid of a cleaning 17 fluid. Depending on the nature of the foulant deposit, 18 cleaning may result in substantial reduction of any increased 19 level of element DWP or BRV, above the base condition, which is attributable to foulant deposits, or may reduce the amount of 21 BRV which is attributable to such deposits.
22 Cleaning Fluid - A cleaning fluid is a fluid, as defined 23 herein, that is sufficiently aggressive toward foulant deposits 24 to accomplish cleaning of the foulants when introduced, with or without aeration gas, in a given concentration and in a given 26 amount, into the gas discharge passages of the diffusion 27 element of a fine pore diffuser. Such fluid may act in any 28 effective mode, such as for example: by dissolving the foulant, 29 especially in the case of precipitated inorganic salt deposits;
by dissolving or otherwise weakening material which attaches 31 the foulant to the diffusion element, thereby destroying or 32 assisting in destroying the bond between the foulant and the '~~..~~~99~

1 element; by poisoning, especially in the case of living 2 foulants which may by poisoning be caused to detach from the 3 diffusion element during and/or subsequent to application of 4 the cleaning fluid: in any other suitable mode; or in a combination of modes.
6 Coefficient of Variation - For purposes of the present 7 invention, the "coefficient of variation" is the quotient 8 obtained by dividing the "standard deviation" by the "mean."

9 The "standard deviation" represents the root mean square of the deviations from the mean of a stated number of bubble release 11 vacuum measurements. The "mean" is the arithmetic average of 12 the aforesaid bubble release vacuum measurements. Optimum 13 accuracy is obtained by determining bubble release vacuum at 14 random points representative of substantially the entire gas discharge surface of t:he element, but we have found that with 16 circular plates we can obtain information that is sufficiently 17 accurate to be useful :by sampling the bubble release vacuum at 18 at least 5 equally spaced points along each of two mutually 19 perpendicular diameters of the plates.

Dynamic Wet Pressure (DWP) - Dynamic wet pressure is the 21 pressure differential between the influent surface of a 22 diffusion element and the hydrostatic head at a point of bubble 23 formation. It is a measure of the resistance to gas flow of an 24 area release diffusion element, including the effects of friction in the gas discharge passages of the element and at 26 the influent and effluent ends of such passages, as well as the 27 effects of surface tension at the effluent ends of the 28 passages. One convenient method for determining the dynamic 29 wet pressure is to determine the difference between the hydrostatic head in the liquid medium at the effluent surface 31 of the diffusion element and the total gas pressure at the 32 influent surface of the element expressed in terms of inches of 33 water gauge.

'~:1.~~'~~U
1 Enhanced Pressures Differential - A dynamic wet pressure 2 differential maintained during gas cleaning which is greater 3 than the differential that would have existed if the only 4 change in apparatus and operating conditions had been the 5 successive removal of foulant deposits by the cleaning gas.
6 Fine Pore Diffuser - The term fine pore diffuser 7 encompasses devices with widely varying designs, features, 8 shapes, materials of construction and methods of operation, 9 such as for example porous ceramic disks, plates, domes and 10 tubes; rigid porous plastic disks, plates, tubes; and 11 elastomeric membrane disks, sheets, and tubes. Their unifying 12 factor is their ability to release fine aeration gas bubbles 13 into an aqueous medium.
14 When new and operating in clear water, these devices are 15 capable of discharging bubbles with an average diameter of 16 about 0.2 inches or less. More preferably, on the basis of 17 bubble count, at least about 70%, still more preferably about 18 85% and most preferably at least about 90% of the bubbles so 19 discharged are about 0.2 inches or less in diameter. In the 20 alternative, or preferably in addition to producing bubbles 21 with the foregoing diameters, these diffusers will produce a 22 headloss due to surface tension of about two inches of water 23 guage when operating in clean water.
24 The foregoing values of bubble diameter and headloss are 25 predicated on operation of the fine pore diffuser at a flux 26 which is characteristic of normal operating conditions for the 27 diffuser or for the process in which it is employed. In the 28 alternative, the above: values of clean water bubble diameter 29 and/or headloss will be produced over at least a portion, and 30 preferably over at least about 10% of, a flux range of about 31 0.25 SCFM to about 25 ,SCFM, more preferably about 0.5 SCFM to '' ~ ~)~~3~.~
.,r .~.

1 about 20 SCFM, and still more preferably about 1 to about 10 2 SCFM.
3 Fluid - A fluid :is a medium which is wholly or at least 4 substantially all liquid, or is wholly or at least substantially all gaseous, as defined herein, or is a fluent 6 mixture of components comprising at least liquid and/or gaseous 7 material, and which may or may not also contain solid 8 materials. If solid materials are present, the amount will be 9 restricted to the extent necessary for the fluid to perform its intended function satisfactorily.
11 Foulant - A "foulant" is any material, present in a liquid 12 medium and/or in an aeration gas, which tends to form a deposit 13 at (including in or adjacent) the inlets and/or outlets of gas 14 discharge passages of a fine pore diffuser or within such passages in such a manner as to affect the gas pressure/flow 16 relationship and/or oxygen transfer efficiency of the diffuser, 17 such as for example by impeding flow or impairing uniformity of 18 distribution of aeration gas discharged through a given element 19 or group of such elements.
The foulant and/or resultant deposits may be of natural 21 and/or synthetic origin, organic and/or inorganic, living or 22 non-living, and composed of liquid, solid and/or gaseous com-23 ponents. Non-limiting examples of the more common foulants are 24 fungal and bacterial strains, algae, protozoa, rotifers, higher life forms, oily residues, organic pipe coatings, soap and 26 detergent residues, dust, rust and other metal oxides, 27 hydroxides and inorganic salts. Examples of these salts 28 include the carbonates and sulfates of such metals as calcium, 29 magnesium, copper, aluminum, iron and other substances which may be suspended in or dissolved in a liquid medium and be 31 rendered less soluble by any means, especially by discharge of 1 aeration gas into the liquid medium at its interface with a 2 diffusion element.
3 The term "present" is employed in this definition in the 4 broadest possible sense so as to embrace foulants which are present in any form of admixture such as, for example, suspen-6 sions, dispersions, emulsions, solutions and other forms.
7 The deposits are usually, but not necessarily, adherent to 8 the diffusion element and tenacious in the sense that under 9 normal conditions of discharge, the aeration gas will not sufficiently remove them from the diffusion elements to 11 overcome their above-indicated effects on gas flow.
12 The term deposits is also used in a broad sense to include 13 solid and/or liquid components in the form of pasty, semi-solid 14 or solid particles or masses, such as for example, slimes, scales and other incrustations.
16 The formation of deposits may occur in any manner such as, 17 for example: by mere lodgment, as when a rust particle borne by 18 aeration gas enters the inlet of a gas discharge passage of a 19 diffusion element and 7.odges within; by accretion, as when tiny oil droplets and dust particles borne by aeration gas adhere to 21 one another and to the influent surface of the element, 22 combining to form a gradually enlarging mass which partly or 23 fully obstructs the inlets of gas discharge passages; by 24 organic growth, as when one or more life-forms present in the liquid medium at the effluent surface of the diffusion element 26 forms layers or networ~ts at such surface which impede the flow 27 of aeration gas or cause coarse bubbling or at least impair 28 uniformity of aeration gas distribution; by ingestion, as when 29 suspended solids in the liquid medium are borne into the gas discharge passages by a reverse flow of liquid medium through 31 the diffusion element when the flow of aeration gas is 1 intentionally or unintentionally suspended: or by precipitation 2 (including crystallization), as when insolubilized inorganic 3 salts are deposited in the gas discharge passages and/or at 4 their outlets during discharge of the aeration gas.
Gas, Gaseous - For- purposes of the present invention a gas 6 or a gaseous material is may be a true gas, or a mixture of 7 such gases, or a vapor, or mixture of vapors, or a mixture of 8 gas and vapor, and may also include entrained liquids or solids 9 in the form of fine or substantially colloidal droplets or particles, which is in the gaseous state to a sufficient extent 11 under conditions of use for forming bubbles when discharged 12 through a fine pore diffusion element into a liquid medium.
13 Mean Hubble Release Vacuum - The arithmetic average of a 14 statistically significant number of bubble release vacuum measurements at randomly or systematically established 16 locations on any surface of a diffusion element.
17 SCFM - This refers to the rate of gas flowing in terms of 18 cubic feet per minute, corrected to a temperature of 20°C, an 19 absolute pressure of 760 mm of mercury and a relative humidity of 36%.
21 Taak Type Process - For purposes of the present invention, 22 a tank type process is a process of discharging aeration gas 23 into an aqueous medium at a rate of at least about 2, more 24 preferably at least about 4, and still more preferably at least about 6 SCFM per :L000 cubic feet of liquid medium.
26 Alternately, or in coma>ination with the foregoing, a tank-type 27 process may be characaerized by an average liquid medium 28 retention time of less than about 48 hours, more commonly less 29 than 24 hours, and quite frequently less than 12 hours.

1 Other Definitions - For definitions of other terms used 2 herein, please refer to the definitions in Schmit et al, U.S.
3 Patent 4,382,867.

The foregoing are but a few of many possible embodiments 6 of the invention, and persons skilled in the art will, with and 7 without application o:f non-obvious modifications, evolve a 8 variety of new or alternative embodiments without departing 9 from the spirit of the invention. It should thus be understood that this patent is intended, and should be construed, to cover 11 all embodiments falling within the scope of the following 12 claims and their equivalents.

Claims (44)

1. Apparatus for aeration of wastewater with an aeration gas, comprising:
A. a tank having wall means including a floor for holding wastewater which is to be aerated by said aeration gas;
B. a multiplicity of fine pore diffusers respectively comprising plenums and diffusion elements which are mounted in a portion of said tank and which will be submerged in said wastewater when said diffusers are in normal operation;
C. cleaning fluid conduits defining one or more cleaning fluid channels 1. running from a source of cleaning fluid to the multiplicity of plenums, and

2. connected with said plenums for simultaneously a. feeding cleaning fluid from said source to said plenums and to the diffusion elements mounted thereon and b. cleaning the diffusion elements; and D. aeration gas conduits defining one or more aeration gas channels separate from said cleaning fluid channel(s), running from a source of aeration gas to said plenums and connected with said plenums for supplying aeration gas thereto separately from said cleaning fluid.
2. Apparatus according to claim 1 wherein said aeration gas channels include aeration gas conduits which will be submerged in said wastewater when said diffusers are in normal operation, and wherein said cleaning fluid conduits include substantially horizontally disposed segments which run along the outsides of said aeration gas conduits to said plenums.

3. Apparatus according to claim 1 wherein said aeration gas channels include areration gas conduits which will be submerged in said wastewater when said diffusers are in normal operation, and wherein said cleaning fluid conduits include substantially horizontally disposed segments which run along the insides of said aeration gas conduits to said plenums.

4. Apparatus for aeration of water, comprising A. a water impound having wall means including a floor for retention of water during aeration thereof;
B. an aeration gas channel 1. including an attachment for connecting the channel with a source of aeration gas and 2. having a plurality of aeration gas conduits, at least portions of which extend generally horizontally within a zone in said impound which will be submerged in said water when said impound is in normal operation;
C. a multiplicity of fine pore diffusers mounted at longitudinally spaced intervals along the lengths of, and in communication with the interiors of, the generally horizontal portions of said aeration gay; conduits;
C. at least one cleaning fluid channel having an inlet for receiving cleaning fluid from a source of such fluid and at least one conduit for conveying such fluid from said inlet to said impound for in situ cleaning of the diffusers, said at least one cleaning fluid channel 1. including plural members within said zone that respectively have substantially separate and substantially direct connections to plural diffusers, and 2. defining cleaning fluid flow paths which remain substantially separate from said aeration gas channel in those parts of said flow paths which extend from said inlet to said diffusers.

5. Apparatus according to claim 4 wherein said diffusers are multi-pore diffusion elements.

6. Apparatus according to claim 4 wherein said diffusers include plenums.

7. Apparatus according to claim 4 wherein said diffusers include plenums and raid aeration gas conduit portions communicate with said diffusers through said plenums.

8. Apparatus according to claim 4 wherein said aeration gas conduit portions communicate with said diffusers to provide flows of aeration gas from said aeration gas channel in the direction of and into said plenums, and said apparatus includes retarding means for substantially retarding flow of cleaning fluid in the reverse direction from said plenums into said aeration gas channel.

9. Apparatus according to claim 4 wherein said aeration gas conduit portions communicate with said diffusers to provide flows of aeration gas from said aeration gas channel in the direction of and into said plenums, and said apparatus includes one-way valve means positioned for substantially preventing flow of cleaning fluid in the reverse direction from said plenums into said aeration gas channel.

10. Apparatus according to claim 4 wherein said diffusers include plenums and said aeration gas conduit portions communicate with said plenums through aeration gas flow regulating means to provide flows of aeration gas of controlled flow rate from said aeration gas channel in the direction of and into said plenums.

11. Apparatus according to claim 10 wherein said aeration gas flow regulating means include one-way valve means positioned for substantially preventing flow of cleaning fluid in the reverse direction from said plenums into said aeration gas channel.

12. Apparatus according to claim 11 wherein said one-way valve means are positioned within said plenums.

13. Apparatus according to claim 4 wherein said diffusers include plenums and said plural members communicate with said diffusers through said plenums.

14. Apparatus according to claim 4 wherein said plural members include plural tee connectors having their base legs connected with the diffusers.

15. Apparatus according to claim 4 wherein said diffusers include plenums having surrounding wall means and said plural members include plural tees having their base legs in communication with the plenums through said surrounding wall means.

16. Apparatus according to claim 4 wherein said plural members communicate with said diffusers to provide flows of cleaning fluid from said at least one cleaning fluid channel in the direction of and into said plenums, and said apparatus includes retarding means for substantially retarding flow of cleaning fluid in the reverse direction from said plenums into said cleaning fluid channel.

17. Apparatus according to claim 4 wherein said plural members communicate with said diffusers to provide flows of cleaning fluid from said at least one cleaning fluid channel in the direction of and into said plenums, and said apparatus includes one-way valve means positioned for substantially preventing flow of cleaning fluid in the reverse direction from said plenums into said cleaning fluid channel.

18. Apparatus according to claim 4 wherein said diffusers include plenums and said plural members communicate with said plenums through cleaning fluid flow regulating means to provide flows of cleaning fluid of controlled flow rate from said at least one cleaning fluid channel in the direction of and into said plenums.

19. Apparatus according to claim 18 wherein said cleaning fluid flow regulating means include one-way valve means positioned for substantially preventing flow of cleaning fluid in the reverse direction from said plenums into said cleaning fluid channel.

20. Apparatus according to claim 19 wherein said one-way valve means are positioned within said plenums.

21. Apparatus according to claim 4 wherein said cleaning fluid channel includes cleaning fluid conduit segments, each of which is positioned for passing cleaning fluid from a position adjacent one of said diffusers to a position adjacent another of said diffusers.

22. Apparatus according to claim 4 wherein said cleaning fluid channel includes cleaning fluid conduit segments which extend generally parallel to said generally horizontally extending portions of said aeration gas conduits within said zone.

23. Apparatus according to claim 4 wherein said cleaning fluid channel includes cleaning fluid conduit segments which extend along the outside of and closely adjacent said generally horizontally extending portions of said aeration gas conduits within said zone.

24. Apparatus according to claim 4 wherein said cleaning fluid channel includes cleaning fluid conduit segments which extend within said generally horizontally extending portions of said aeration gas conduits within said zone.

25. Apparatus according to claim 4 wherein said inlet is connected with a source of cleaning fluid.

26. Apparatus according to claim 25 wherein said source is a source of cleaning liquid.

27. Apparatus according to claim 25 wherein said source is a source of cleaning gas.

28. A method of assembly apparatus for aeration of water with an aeration gas, comprising fabricating aeration gas distributor assemblies by:

A. securing to an aeration gas distribution conduit that is useful for defining at least a portion of an aeration gas channel, a plurality of plenums that are disposed at intervals of distance longitudinally along said conduit and are configured to receive diffusion elements useful for aerating water, and B. securing to said plurality of plenums one or more cleaning fluid distribution conduits respectively defining a cleaning fluid channel that is substantially separate from said aeration gas channel for supplying cleaning fluid to said plenums substantially separately from said aeration gas.

29. A method according to claim 28, further comprising:
A. providing said plenums and said aeration gas conduit in forms constructed of synthetic resinous material;
B. securing to said plenums diffusion elements for diffusing aeration gas into water;
C. supporting a plurality of said aeration gas conduits substantially horizontally in a tank which in normal operation will contain water to be aerated;
D. connecting said aeration gas conduits with a source of aeration gas comprising oxygen;
E. supporting raid cleaning fluid conduits in said tank; and F. securing said cleaning fluid conduits to an inlet for connection to a source of cleaning fluid which is aggressive toward organic or inorganic foulants.

30. A method of assembling apparatus for aeration of water with an aeration gas, comprising fabricating aeration gas distributor assemblies by:

A. securing to an aeration gas distribution conduit that is useful for defining at least a portion of an aeration gas channel, a plurality of plenums that are disposed at intervals of distance longitudinally along said conduit and are configured to receive diffusion elements useful for aerating water, and B. securing to said aeration gas distribution conduit at least a portion of a cleaning fluid distribution channel which includes one or more cleaning fluid distribution conduits and further includes connectors that are coupled to said cleaning fluid distribution conduit(s) and are spaced longitudinally along said cleaning fluid distribution conduit (s) at the same intervals as, and are connected to, said plenums.

31. A method according to claim 30, further comprising:
A. supporting an aeration gas manifold conduit horizontally in a tank and connecting one end of said aeration gas manifold conduit with an attachment for connecting said conduit with an aeration gas source;
B. supporting a cleaning fluid manifold conduit horizontally in the tank and connecting one end of said cleaning manifold conduit with an inlet for connecting said conduit with a cleaning fluid source;
C. supporting said aeration gas distribution conduits horizontally in the tank and connecting said aeration gas distribution conduits to said aeration gas manifold conduit; and D. connecting said cleaning fluid distribution conduit(s) to said cleaning fluid manifold conduit.

32. A method according to claim 30, wherein said cleaning fluid distribution conduits are respectively secured outside said aeration gas distribution conduits.

33. A process according to claim 30, wherein said cleaning fluid distribution conduits are respectively secured inside said aeration gas distribution conduits.

34. A method according to claim 30, wherein said cleaning fluid distribution conduits are respectively secured partially inside said aeration gas distribution conduits and partially outside said aeration gas distribution conduits.

35. A process according to claim 33, wherein said aeration gas distribution conduits have joints for passing cleaning gas from outside said aeration gas distribution conduits to inside said aeration gas distribution conduits.

36. A method of assembling apparatus for aeration of water with an aeration gas, comprising:
A. fabricating at least a portion of a cleaning fluid channel comprising cleaning fluid conduit and plural tee connectors positioned at longitudinally spaced intervals along said cleaning fluid channel portion, said tee connectors having base legs projecting laterally from said cleaning fluid channel portion;
B. fabricating at least a portion of an aeration gas channel comprising aeration gas conduit having plural longitudinally spaced plenums secured thereto, such plenums 1. being configured to receive diffusion elements, 2. being spaced apart by intervals substantially similar to those of the tee connectors, and 3. having walls with holes therethrough for receiving said tee connector base legs; and C. securing said cleaning fluid channel portion to said aeration gas channel portion by securing said tee connector base legs in communication with said holes.

37. A method according to claim 36, wherein said holes extend from the interiors of said plenums to the exteriors of said plenums, outside said aeration gas conduit.

38. A method according to claim 36 wherein said cleaning fluid channel portion is secured inside said aeration gas channel portion and said tee connector base legs communicate with the interiors of said plenums through openings in the aeration gas conduit that are spaced apart longitudinally alone said conduit by intervals substantially similar to those of the tee connectors.

39. A process for aerating water with aeration gas, comprising:
A. conducting a flow of aeration gas from a source of said gas along a first flow path;
B. delivering said aeration gas via said first flow path to a multiplicity of fine pore diffusers submerged, distributed and spaced apart from one another in one or more horizontally disposed arrays in a body of water and respectively having diffusion elements which are subject to accumulation of foulant in and/or on the elements;
C. introducing said aeration gas into said diffusers through connections between said first flow path and said diffusers for causing discharge of said aeration gas through said diffusion elements, thereby aerating the water;
D. conducting a flow of cleaning fluid which is aggressive toward such foulant from a source of said cleaning fluid along a second flow path;
E. delivering said cleaning fluid to said multiplicity of diffusers via said second flow path;

F. maintaining said flow of cleaning fluid substantially separate from said first flow path until said cleaning fluid reaches said diffusers, and G. introducing said cleaning fluid into said diffusers from said second flow path for causing discharge of said cleaning fluid through said diffusion elements for cleaning said elements.

40. A process according to claim 39, wherein:
A. said first flow path includes a substantially horizontally disposed portion which will be submerged in said water when said diffusers are in normal operation;
B. said second flow path includes a portion which connects with such diffusers and which will be submerged in said water when said diffusers are in normal operation; and C. at least part of said portion of said second flow path, including the part thereof which connects with said diffusers, is maintained outside said horizontally disposed portion of said first flow path.

41. A process according to claim 39, wherein:
A. said first flow path includes a substantially horizontally disposed portion which will be submerged in said water when said diffusers are in normal operation; and B. said second flow path includes a portion which connects with such diffusers and which will be beneath the surface of said water when said diffusers are in normal operation; and C. at least part of said portion of said second flow path, including the part thereof which connects with said diffusers, is located inside said horizontally disposed portion of said first flow path.

42. A process according to claim 39, wherein said diffusers include plenums arranged in sets, and said first flow path includes branches each connecting with a different set of plenums.

43. A process according to claim 40, wherein at least part of the first flow path is in a first conduit and at least part of the second path is in a second conduit which is bound to the exterior of said first conduit.

44. A process according to claim 40, wherein at least part of the first flow path is in a first conduit and at least part of the second path is in a second conduit extending through the interior of said first conduit.