WO2011161327A1

WO2011161327A1 - A process for treating waste water comprising organic material

Info

Publication number: WO2011161327A1
Application number: PCT/FI2011/050611
Authority: WO
Inventors: Frederico Varalta
Original assignee: Preseco Oy
Priority date: 2010-06-24
Filing date: 2011-06-27
Publication date: 2011-12-29
Also published as: FI20105736A0

Abstract

The invention relates to a process for treating waste water (W_w) comprising organic material, wherein waste water (W_w) originates from a food industry plant, such as from a slaughterhouse or a dairy, the process comprising a step for feeding waste water (W_w) to a first purification phase, such as to a drum screen (2), for separating the coarsest solid debris from waste water (W_w), a step for feeding waste water (W_w) from the first purification phase to a second purification phase, a step for floating waste water (W_w) in a second purification phase, such as in a flotation unit (4), for removing solid debris and flocculated matter from waste water (W_w), a step for feeding waste water (W_w) from the second purification phase to a discharge outlet (56), and a step for discharging purified water through the discharge outlet (56). Waste water (W_w) is fed from the second purification phase to the discharge outlet (56) via an additional purification phase for filtering waste water (W_w) with a filter (53) comprising filter mass grains.

Description

A process for treating waste water comprising organic material

Field of the invention

The invention relates to a process for treating waste water comprising organic material as defined in the preamble of the independent claim 1.

The invention relates to a water treatment process for water that has a big solid matter content, high chemical oxygen demand and/or high biological oxygen demand. The water treatment process is suitable for purifying waste water that comes for example from a slaughterhouse, a dairy or any other food industry plant also paper industry waste water can be treated with the water treatment process presented here.

Filtration is a mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass. Filtration is based mainly on physical and chemical reactions between the filtering material and the filtered substance. The filtering material can be for example sand, plastic filling materials or ceramic bodies. The filters can be divided into slow filters and rapid filters based on the filtration rate of the water. A slow filter has the filtration rate of water in the range of 0.1 - 0.5 m/h. A significant part of the purification in slow filters is based on biological activity taking place on the surface of the filter. Rapid filters have essentially higher filtration rate than the slow filters. The filtration rate can be, for example, 2 - 50 m/h. Biological activity does not have so great importance in rapid filtering as in slow filtering.

When treating waste water it is essential how efficiently the water treatment apparatus can be cleaned. Traditionally filter cleaning can be done by water or by air or by their combination. During the cleaning period the apparatus is out of use, and also waste waters are formed in it. These must be conducted among waste waters.

Traditionally solid particles can be removed from a slaughterhouse waste water by physicochemical treatment (coagulation-flocculation process) using aluminium sulfate as the coagulant, and activated silica, powdered activated carbon, precipitated calcium carbonate, polyacrylic acid, or anionic polyacrylamide as coagulant aids to improve the settling time.

EP 1 428 564 Al discloses a water treatment apparatus especially for treatment of clean water but also for waste waters. The water treatment apparatus comprises one or more containers equipped with gas space and the apparatus has one or more water treatment units, which can be for example a filter, such as a mechanical filter or a bio-filter, screen, flotation apparatus, coagulation apparatus or flocculation apparatus. An ejector is attached to the upper part of the container and linked to the lower part of the container by a connecting device. Gas and water are conducted to the upper part of the container and from the ejector the gas-water mixture is conducted by means of the connecting device to the lower part of the container in order to intensify the washing of the water treatment unit and/or the container. The upward flowing water and gas bubbles mix the bio-filter mass and transport dirt material to the discharge unit.

Objective of the invention

The object of the invention is to provide an effective water treatment process for waste water such that the need of chemicals in the water treatment process can be minimized.

Short description of the invention

The process for treating waste water comprising organic material is characterized by the definitions of the independent claim 1.

Preferred embodiments of the process are defined in the dependent claims 2 to 9.

The invention is based on a water treatment process for treating waste water comprising organic material, wherein waste water originates from a food industry plant, such as from a slaughterhouse, a dairy or any other food industry plant where waste water has a high COD (chemical oxygen demand), BOD (biological oxygen demand) or solid matter content. Waste water comes to the water treatment process from influent conduit and is first treated in at least one drum screen in order to separate coarsest solid debris from waste water. From the drum screen waste water is sometimes arranged to move to an equalization basin which comprises blender and at least one pump and where the incoming waste water flow is equalized and waste water's pH can also be adjusted. The equalization basin is not essential but when the process is running all the time without any breaks the basin acts as a spare water reserve in the process. The coarsest solid debris that is separated in the drum screen from waste water is moved from the drum screen preferably straight to disposal unit. From the equalization basin or straight from the drum screen waste water is flown toward the flotation unit and between the equalization basin and the flotation unit chemicals may be added to waste water in order to increase for example alkalinity in waste water. Coagulants and flocculants are added to waste water before it gets to the flotation unit where the solid matter and flocculated matter, such as sludge and scum, are removed from waste water and led to a storage tank wherefrom they are led for example to a filter belt press and further to disposal. On the other hand flotation does not remove soluble matter so the solid matter and for example phosphorus are removed effectively but organic matter only to some extend while most of the organic matter still remains in waste water.

The main idea of the water treatment process according to the invention is that waste water is further fed from the flotation unit to an additional purification step such as to a separate water treatment apparatus which comprises a filter. This additional purification step improves the purity level of drain water and also decreases the amount of chemicals required in the floatation. The amount of chemicals needed in the floatation decreases substantially, at most by half what is normally used and also drain water has more uniform quality. The reason for decreasing the amount of chemicals needed in the floatation is because without the additional purification step the flotation is the last step before discharging purified waste water to the final destination or to storage for purified water and all the impurities have to be taken away with the help of chemicals. Because of the additional purification step waste water coming from the flotation does not need to be completely purified and there can be impurities that are purified in the additional purification step. So the need of chemical will diminish substantially.

The process for treating waste water comprises a step for feeding waste water to a first purification phase, such as to a drum screen, for separating the coarsest solid debris from waste water, a step for feeding waste water from the first purification phase to a second purification phase, a step for floating waste water in a second purification phase, such as in a flotation unit, for removing solid debris and flocculated matter from waste water, a step for feeding waste water from the second purification phase to a discharge outlet, and a step for discharging purified water through the discharge outlet. Waste water is fed from the second purification phase to the discharge outlet via an additional purification phase for filtering waste water with a filter comprising filter mass grains. The process works by using in the additional purification phase a container in which the filter is arranged, and by feeding waste water in the container above the filter so that waste water flows down in the container and through the filter for lodging particles from waste water to produce purified waste water. Purified waste water that has been purified by the filter is fed from the container through a tube arrangement that is at least partly arranged inside the container and that is in a flow communication with the discharge outlet.

The water treatment apparatus comprises a container where waste water is fed from the flotation unit. Waste water is led from the flotation unit to the water treatment container such that waste water flows down in the container and during the down flow the organic flocks lodge to a filter arranged inside the container. The filter comprises filter mass which is preferably arranged in layers such that fine mass grains are on the lower layers of the filter mass, i.e. on the bottom of the container, and the coarser and bigger grains are on the upper layers of the filter mass. The filter comprises basically coarser filter mass grains than what is used when treating drinking water although the lowest layers of the filter mass can comprise also fine grains. The filter mass grains are arranged in filter mass layers comprising diverse filter mass grains. The filter mass grains have preferably large pore volumes and surface areas so that they are suitable for a biofilm process. The size of the filter mass grains is preferably between 4 - 8 mm and the density of the filter mass grains is preferably between 1200 - 1500 kg/m while sand as filter mass has too fine particles for this purpose. Sand as a filter mass is known from other waste water systems in which waste water does not contain organic matter. Depending on waste water that is purified many kinds of filter masses can be used in the water treatment apparatus. The filter mass can comprise grains that have different density in different layers such that the heaviest grains are on the bottom layers of the filter mass and the lightest grains are on the top layers of the filter mass. The filter mass can also comprise grains in different sizes such that small grains are on bottom layers of the filter mass and big grains are on top layers of the filter mass. The idea with the different layers is that the coarser grains lodge biggest particles from waste water and the smaller grains lodge the smallest particles from waste water such that after water has flown through all filter mass layers water is purified and it is fed to a collector pipe to be led to a storage for purified water and from there to a discharge outlet. The purification process is continuous unless there is a need to clean the filter.

Waste water comprises particles in different sizes so the filter mass has to be able to lodge waste water particles at all sizes so the right size of the filter mass grains is essential. If the filter mass has too fine grains, the filter will block up too often and the waste water treatment process need to be interrupted constantly because of the cleaning process. The filter mass is ideal for the organic flocks to grow and there will not be needed any mechanical removers. Air is preferably not led to the container at the same time with waste water because of the idea that the organic flocks can lodge to the filter mass and grow there without disturbances so that they do not end up again to the water that is flown through the filter mass.

When the filter is full of organic flocks, the water level moves upward in the container and the water level indicator will cause an alarm which causes waste water discharge outlet to be closed and a cleaning process to be started. In other words the container used in the additional purification phase comprises an indicator for alarming if the water level in the container rises above a pre-set level. The waste water inlet does not need to be closed and waste water can be fed to the container at the same time with the cleaning process. The water treatment process further comprises a cleaning step for removing organic material from the filter by closing the discharge of purified waste water from the container, feeding cleaning water through a tube arrangement arranged at least partly in the container and dispersing said cleaning water from the tube arrangement below the filter in the container for feeding cleaning water upwards through the filter for cleaning the filter and discharging cleaning water from the container through an additional discharge outlet arranged above the filter. In other words when the filter has to be cleaned a separate cleaning process is started in which water is circulated through the container and through the filter mass so that the filter mass will be cleaned. At the same time with the cleaning water feed the container can be shaken so that the organic flocks will more easily detach the filter mass grains. Another way to make the cleaning process more effective is to feed water and gas mixture as a cleaning medium and the water - gas mixture is fed with pressure so that when the water - gas mixture goes through the filter mass, the filter mass will vibrate. The pressure of cleaning water is preferably 10 bar. When the discharge outlet for purified water is closed the water level in the container rises and eventually organic flocks and cleaning water is discharged preferably through an overflow pipe or a discharge outlet. The discharged water coming from the overflow pipe or from the discharge outlet goes preferably back to the equalization basin if there is one or to the flotation unit. When the filter mass is clean again the water treatment process can continue and the waste water discharge outlet will be opened.

The additional purification step such as the separate water treatment apparatus is preferably a standing container comprising a water inlet for waste water to be fed inside to the container, a filter comprising filter mass for filtering waste water so that the organic material will be removed from waste water and a water outlet for discharging water that has been purified. Waste water is fed to the container through a water inlet and preferably gushed or sprayed or otherwise distributed all over the container such that the filter can act evenly. For example water can be fed to a separate collector which delivers water for example through pipes that circulate and disperse water so that it reaches the filter mass everywhere in the container. The container preferably comprises a pipe or a tube inside the container, for example in the middle of the container, such that water flown through the filter mass is led to the tube and through the tube to the discharge outlet and preferably to storage for treated water. The tube preferably comprises tube sections that have holes so that water can go through holes to the tube sections and through the tube sections to the tube. The tube sections are preferably on the bottom of the container and connect to the main tube in the middle of the container. The tube sections preferably comprise a filter to restrain the filter mass grains to go into the tube sections. Cleaning water is arranged to be fed inside to the container through the same tube that is arranged to feed purified water to the discharge outlet. Though the flow inside the tube is in the cleaning process reverse than what it is in the purification process. The cleaning water is discharged through an outlet for the cleaning water which is for example an overflow pipe.

In an other embodiment of the invention the water treatment process comprises at least two additional purification steps in which case waste water is preferably fed from the flotation unit to a distribution chamber wherefrom it is divided to separate purification steps which can be identical.

List of figures

In the following the invention will be described in more detail by referring to the figures, in which

Fig 1 shows a flow sheet of a water treatment process comprising an additional purification step according to the invention, and

Fig 2 shows the water treatment apparatus used in the water treatment process according to the invention. Detailed description of the invention

The figure 1 shows an example of a flow sheet showing the process for treating waste water according to the invention. Influent 1 is waste water comprising organic material from a food industry plant such as from a slaughterhouse or a dairy. Waste water flows to a drum screen 2 for separating biggest particles from water. Waste water flows from drum screen to an equalization basin 3 for equalizing waste water and for adjusting pH if needed. The equalization basin 3 is not essential in the process but it is used in situation where the process is not running around the clock but for example only 8 hours per day. From the equalization basin 3 or alternatively straight from the drum screen 2 (this alternative is not shown in the figure) waste water flows to a flotation unit 4 for removing solid debris and flocculated matter from waste water. Before waste water reaches the flotation unit chemicals are added to the water but because of the additional purification step the need for the chemicals is less than what it normally is. From flotation unit 4 waste water flows to the additional purification step which is preferably a separate water treatment apparatus 5 comprising a container and a filter for purifying waste water. From the water treatment apparatus 5 purified water is led to a treated water storage 6 and then discharged or when the water storage 6 is not needed water can be discharged directly (not shown in the figure). Water from the treated water storage 6 can be used as cleaning water when the container needs to be cleaned. The dashed line shows the cleaning process flow. The cleaning process starts when the water level in the water treatment apparatus 5 rises and an alarm or other indicator sets the signal for the cleaning process to be started. First the discharge outlet for purified water is closed and then cleaning water starts to flow from the water storage 6 to the water treatment apparatus 5 which is shown as a dashed line. The cleaning process will be described in more detail in the next figure. Cleaning water is finally discharged from the water treatment apparatus 5 and led to the equalization basin 3 or to the flotation unit 4 to be processed again.

Figure 2 shows an example of a water treatment apparatus 5 in which waste water is purified according to the invention. Waste water W_w is fed through a water inlet 55 to the container 51 and flows down inside the container 51 and through a filter 53. The water inlet 55 can be for example a tube-like inlet or an open top in a container 51 like in this figure. The filter 53 is arranged inside to the container 51 and preferably to the lower part of the container 51 and comprises filter mass layers 54. The filter mass layers 54 comprises filter mass grains such that on the upper layers the grains are preferably quite big in size in order to lodge the biggest particles from waste water W_w and in the lowest layers the filter mass grains are preferably quite small in order to lodge the smallest particles from waste water. A tube arrangement is arranged at least partly inside the container 51 wherein a tube 52 is arranged 51 preferably in a vertical direction in the middle of the container 51 and such that near the bottom of the container 51 the tube 52 is divided preferably into at least two horizontal or almost horizontal tube sections 52a. The tube sections 52a can also be arranged in another position than horizontal direction but they preferably follow the container's 51 bottom part. The tube sections 52a have holes through which water W_w flows and the holes preferably comprise filters which keep filter mass grains outside of the tube sections 52a. The tube 52 has preferably a vertical or almost vertical water discharge outlet 56 preferably above the filter 53 such that water W_w that has flown through the filter 53 is led through the tube section 52a and the tube 52 and arranged to flow out of the container 51 through a water discharge outlet 56. The water discharge outlet 56 leads water W_w to a separate treated water storage or discharges it straight to the final destination. The container 51 also comprises an additional discharge outlet 57 for cleaning water W_c to be fed outside of the container 51. The additional discharge outlet 57 for cleaning water W_c can be for example an overflow pipe.

Waste water W_w is flown to the container 51 through the water inlet 55 and it flows down the container 51 through the filter 53 such that the coarsest particles from waste water W_w are lodged the upper layers of the filter mass 54 and the finest particles are lodged the lowest layers of the filter mass 54. In the bottom of the container 51 water W_w is led to tube sections 52a through holes that comprise preferably filter in order to keep filter mass grains outside the tube sections 52a. From tube sections 52a water W_w is flown to the tube 52 and through the tube 52 to the discharge outlet 56. When the filter 53 contains too much particles in order to operate normally the water level will rise and an alarm will give a signal to a cleaning process to be started.

When the cleaning process starts the discharge outlet 56 for purified water W_w is first closed after which cleaning water W_c is led from the treated water storage to the tube 52. At the same time with cleaning water W_c air A is also fed to the tube 52 so that the water - air mixture is arranged to flow downwards through tube 52 with pressure and along the tube sections 52a such that when the water - air mixture is discharged through the holes of the tube sections 52a with pressure the water - air mixture will shake the filter mass layers 54 and water W_c will go through the layers 54 and release the particles. While the water discharge outlet 56 is closed the water level will rise and eventually cleaning water W_c with particles will be discharged through an additional discharge outlet 57 such as an overflow pipe. Cleaning water and particles are preferably fed to the equalization basin or to the floatation unit.

It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims

1. A process for treating waste water (W_w) comprising organic material, wherein waste water (W_w) originates from a food industry plant, such as from a slaughterhouse or a dairy, the process comprising:

- a step for feeding waste water (W_w) to a first purification phase, such as to a drum screen (2), for separating the coarsest solid debris from waste water (W_w),

a step for feeding waste water (W_w) from the first purification phase to a second purification phase,

- a step for floating waste water (W_w) in a second purification phase, such as in a flotation unit (4), for removing solid debris and flocculated matter from waste water (W_w),

a step for feeding waste water (W_w) from the second purification phase to a discharge outlet (56), and

- a step for discharging purified water through the discharge outlet (56), characterized in that waste water (W_w) is fed from the second purification phase to the discharge outlet (56) via an additional purification phase for filtering waste water (Ww) with a filter (53) comprising filter mass grains.

2. The process according to claim 1, characterized

- by using in the additional purification phase a container (51) in which the filter (53) is arranged, and

- by feeding waste water (W_w) in the container (51) above the filter (53) so that waste water (W_w) flows down in the container (51) and through the filter (53) for lodging particles from waste water (W_w) to produce purified waste water.

3. The process according to claim 2, characterized in that purified waste water that has been purified by the filter (53) is fed from the container (51) through a tube arrangement that is at least partly arranged inside the container (51) and that is in a flow communication with the discharge outlet (56).

4. The process according to any of claims 1 - 3, characterized by arranging the filter mass grains in filter mass layers (54) comprising diverse filter mass grains.

5. The process according to any of claims 1 - 4, characterized by using filter mass grains having the size between 4 - 8 mm.

6. The process according to any of claims 1 - 5, characterized by using filter mass grains having a density between 1200 - 1500 kg/m .

7. The process according to any of claims 2 - 6, characterized in that the container (51) used in the additional purification phase comprises an indicator for alarming if the water level in the container (51) rises above a pre-set level.

8. The process according to any of claims 1 - 7, characterized in that the process further comprises a cleaning step for removing organic material from the filter (51), by:

closing the discharge of purified waste water from the container (51), feeding cleaning water (W_c) through a tube arrangement (52, 52a) arranged at least partly in the container (51) and dispersing said cleaning water (W_c) from the tube arrangement (52, 52a) below the filter (53) in the container (51) for feeding cleaning water (W_c) upwards through the filter for cleaning the filter (53), and

discharging cleaning water (W_c) from the container (51) through an additional discharge outlet (57) arranged above the filter (53).

9. The process according to claim 6, characterized by feeding air (A) along with cleaning water (W_c).