CA1055420A

CA1055420A - Photooxidative destruction of organic wastes

Info

Publication number: CA1055420A
Application number: CA243,846A
Authority: CA
Inventors: Gilbert R. Seely
Original assignee: Gilbert R. Seely; Charles F. Kettering Foundation
Current assignee: CHARLES F KETTERING FOUNDATION
Priority date: 1975-02-21
Filing date: 1976-01-20
Publication date: 1979-05-29
Also published as: GB1519736A; US3951797A

Abstract

Abstract of the Disclosure A method for promoting the photooxidative destruction of organic waste pollutants by use of gelled metal alginate particles which have been stained with a dye sensitizer. The stained particles are both recoverable and biodegradable. They are effective in promoting the photooxidation of organic wastes including toxic phenol compounds in the presence of visible light and atmospheric oxygen.

Description

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Background of the Invention ~ -This invention relates to a method for promoting the photooxidative destruction of organic wastes and, more parti- -cularly, to a method utilizing particles of a biodegradable gelled metal alginate which have been stained with a sensitizing dye.
In recent years a justifiable concern has arisen over the presence in water supplies of organic waste pollutants.
Among the more toxic constitutents of effluents are phenols, cresols, xylenols, polyphenols, etc~, which are introduced into ~-the environment from chemical, petrochemical and plastics industries, refineries and coke ovens, and even from decaying vegetation. In a recent report to the United Nations Food and Agriculture Organization (Water Res., 7, 929-41 (1973)), the limit on combined phenols was recommended to be 1 ppm to ensure survival of salmonoids and 2 ppm for coarse fish.
The problem is compounded when water is treated with chlorine for municipal use. Chlorine reacts with phenols in the ppm range to produce o- and ~-chlorophenols up to 2,4,6-~20 trichlorophenol. Because of the off-taste and the odor arising from p-chlorophenol in water, the U. S. Public Health Service (1962) suggested a limit of 0.001 ppm of phenol in drinking water. This is lower than that for cyanide and arseni~c. ~`
Toxicity o these phenols to fish is also greater than that of the unchlorinated phenols.
An outline of these problems and some of the current solutions is given in J. E. Zajic, "Water Pollution, Disposal and Reuse", Vol. 2, pp. 418-426 (1971). There, Zajic reports.
that the following treatments for phenolic wastes may be used:
30 ~ 1) solvent extraction, Z) steam stripping, 3) adsorption, 4) ion exchange, 5) chemical degrada*ion and 6) biological degradation.

- 2 -~L~55421~) If the phenol concentration is high enough, recovery by solvent ex~raction or steam stripping may be economically feasible. However, phenol concentrations in most industrial affluents are not sufficiently high to justify such procedures.
For this reason, phenols in dilute industrial effluents are usually adsorbed on activated carbon, for which they may be recovered. On the other hand, Zajic lists several limitations to this method, Vi7.: lack of continuity in the process and contamination of the activated carbon by tars and tar acids beyond regeneration. ;
Similarly, because of their toxicity to most micro~
organisms, biodegradation of phenols is slow; however, the products are non-toxic, andthis is a feasible method of treatment if the concentration is not too high. Chemical oxidation by ~ -ozone, chlorine or potassium permanganate is the fastest de-gradative treatment, but the cost in power and chemcials is --high. In addition, as Zajic notes, with elemental chlorine precaution must be taken to ensure complete reaction of the phenol or the partially chlorinated phenol derivatives impart objec-tionable taste and toxicity to the water.
For these reasons, photooxidation has been studied as a possible solution to the problem. It is attractive because instead o~ requiring stoichiometric quantities of eleatrically or electronically produced oxidants, such as chlorine or ozone, the reaction takes place in the presence of sunliyht, air and catalytic quantities of a promoter. Zinc titanate, zinc oxide, titanium dioxide and beach sand have been found to promote photo-catalytic oxidation of dissolved organic matter on irradiation with sunlamps. See Kinney et al~ "Photolysis Mechanisms for ~30 Pollution Abatement", Report No. TWRC-13, U. S. Dept. of Interior, Federal Water Pollution Control Adm., Ohio Basin Region, Cincinnati, Ohio, October 1969.

- 3 -.t ~ ~r Dye sensitizers have also been used. Thus, Sargent and Sanks in a recent presentation at t~e Photochemical Reaction Engineering Symposium of the American Institute of Chemical -Engineers in Washington, D. C., December 1-5, 1974, entitled "Dye Catalyzed Oxidation of Refractory Organic Wastes Using Visible Light Energy" explained that the reaction sequence for dye sensitization involves absorption of light energy by the dye, transfer of dye energy to dissolved oxygen to form energized oxygen, and oxidation of the organic waste by the energized oxygen.
Accordingly, Sargent and Sanks describe the use of dyes in a homogenous solution to promote aerobic photooxidation -of organic wastes. While this system suffers from the instability of the dye in the homogeneous phase and the need to stain large volumes of water effectively, Sargent and Sanks find it pre~
ferable to the resin-bound d~es which they also tested since binding to ion exchange resins was found to reduce the e~ec-tiveness of the dye as a sensitizer and slow down the reaction as compared to dissolved dyes.
Still, it would be desirable for the sensitizing dye to be bound to a particulate material since txeatment with homogeneous phase dyes results in an intermixing of the dye and the water treated which may be objectionable; whereas, with stained solid particles the phases remain separate. Similarly, use of heterogeneous phase dye-stained particles permits easy recovery of the stained particles by sedimentation or screening, allowing for reclaiming, restoring or reusing. It would also be particularly desirable if a biodegradable base material could be used since this would allow for distribution of the stained particles in polluted lakes and ponds in a one-time application without any detximental environmental effect.

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In regard to resin~bound d~e sensitizers, it is noted that Blosse~, Neckers, Thayer and Schaap in an article entitled "Polvmer-Base Sensl`tizers for P~otooxidants" in the Journal of the American Chemical Society, 95:5820 (1973) report on the use of a Rose Bengal polymer-based reagent to sensitize the generation of singlet molecular oxygen for promoting photochemical reactions.
The base used was an insoluble styrene divinylbenzene copolymer bead. This material, however, is not biodegradable and would be difficult to regenerate.
Accordingly, the need still exists for an effective polymer-based dye sensitizer for promoting photooxidative destruction of organic waste, especially a material which would be biodegradable while at the same time stabilizing the dyes to prolong their useful life over that which they evidence in homogeneous phase systems.
Summary of the Invention The present invention fills this need by providing a feasible method of promoting photooxid~tion of organic waste materials, including phenolic compounds. The method involvés the use of gelled metal alginate particles. The particles are stained with an appropriate sensitizing dye which will photo-catalytically generate singlet oxygen in the presence of sun-- - light or artificial light for effective destruction of the oxidizable pollutants contained in the organic was~es.

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In one aspect the invention provides a method for photooxidative destruction of organic wastes found in aqueous effluents utilizing a dye sensitizer to promote the oxidation of said organic wastes by air or oxygen in the presence of visible light, at an at least weakly alkaline pH and under other ; process conditions operable to effect the photooxidation wherein .

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the improvement comprises using as the promoter biodegradable, gelled metal alginate particles selected from the group consisting of barium alginate, calcium alginate, strontium alginate, and aluminum alginate beads which have been stained with a dye sensitizer selected from the group consisting of the `;
acridine, thiazine, triphenylmethane, phenazine, phthalocyanine classes of cationic dyes, the dye to alginate normality ratio being in the range of 1:30 to 1:200. .;
It is known that most organic waste molecules are -~
not destroyed by direct absorption of visible light, but that when oxygen is excited to a singlet state, it becomes a strong : oxidizing agent capable of oxidizing many ordinarily refractory organic compounds. It is also known that various dyes sensitize or catalyze in situ the generation of~singlet oxygen. The present invention utilizes those known principles in providing a means to effectively oxidize polluting orga~ c compounds. -:
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~L~554zo In addition to providing the known sensitizing function of homogeneous dye systems, however, t~e dye-stained alyinate particles present a heterogeneous phase which has a number of advantageous features. Most significantly, there is no need to separate the dye from the water treated as occurs when a homogeneous dye system is used. In addition, the particles do not, as a rule, introduce a new toxic mate~ial into the environ-ment they are intended to treat since alginate is known to be both non-toxic and biodegradablè ~in fact it is a common bulk additive to food products). Likewise, the dyes used are not notably toxic, and are slowly degraded under conditions of use.
Unlike ion exchange resin particles, alginate particles stabilize the dyes in an active state and prolong their useful 1ife over that which they evidence in homogeneous phase systems.
The gelled particles are mechanically and chemically resistant to deterioration under contemplated conditions of use and may, thus, be reclaimed, restained, and reused several times without .
serious loss of efficiency.
These properties make it possible to treat lndustrial ef1uents containing organic wastes, such as phenols at con-centrations below that for economical recovery, in sunlit lagoons, riffle beds, or in batch or continuous column reactors. It is also possible to use the stained alginate particles for broad-cast application of the particles in lake's, rivers or estuaries where a pollution problem exists. In the latter application, the particles would require no further attention or recovery since they are degraded natural1y to harmless derivatives in a reasonable time.
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ion-exchange process can be used to replace the ions in already gelled particles ~ith dIfferent metal ~ons of the particular type desired. In either event, a gelled metal alginate is formed having metal ions available to act as binding agents for the dye.
Barium, calcium, strontium and aluminum alginates are preferred, but alginates of lead, iron, copper and other divalent metal ions can be used if desired.
The particles are stained by immersion in a solution containing a suitable sensitizing dye which will bind to the alginate paLticles. Most of the dye may be incorporated into the gelled alginate particle within a few minutes, but it takes about a day for it to be distributed evenly throughout. ~or the most part cationic dyes which have marked aggregating or metachromatic properties are used. Examples of the types of .... ........ ..
dyes possible include the acridine, thiazine, triphenylmethan`e, phenazine and phthalocyanine classes, with the thiazine dyes being preferred. It is believed that much of the dye in the particle is in an aggregated, photochemically inactive form, but is in equilibrium with the monomeric, photochemically active form. In any~case, the stability of the dyes against chemical and photochemical degradation is markedly increased by binding to the gelled alginate particles. The amount of dye bound to the particles can vary all the way to a 1:1 ratio, depending on the economic considerations, but generally the preferred alginate normality ratios are in the range of 1:30 - 1:200.
The dye i9 usually destroyed or much depleted by an exhaustive photosensitized oxidation reac~ion. Also the dye is sometimes removed from the alginate particle by complexing : .. . .
with oxidation products of the organic waste, but this dye is still photoactive and may continue photosensitizing the reaction ; ;
in the homogeneous phase.
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-~(~SS~L20 It is known that dye sensitized photooxidation of phenols increases with pH at least ~o pH 10. Thus, with phenols it is necessary to have a medium which is at least weaXly alkaline (pH ~ 9) to get photooxidation because only the phenolate ion is attacked. Since the gelled alginate particles are neutral, it is thus necessary to add alkali to the solution if oxidation is to be favored. Furthermore, if the products of the reaction are acidic, the medium must be neutralized if the reaction is to be maintained.
One approach to this problem is to simply add to the effluent to be treated (if it is not already alkaline) a basic material which will adjust the pH upward and permit the reaction to go forward. H^owever, in the case of lagoons or natural waters, -this may not be feasible. Therefore, another possible approàch is to establish basic conditions within the gelled alginate particle itself. This obviates the need to add alkali to the entire medi~m. It may be done by milling slightly soluble basic substances into the alginate solution before gelling. Any compatible alkaline filler having a proper soluhility and basic ~o reaction on hydrolysis may be used. Examples are magnesium oxide, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, and mixtures thereof. Thus, it is possible to .
oxidize phenols without addition of alkali to the medium, and in some cases, without the medium becoming alkaline at all. In ;
addition, it has been found that the presence of the basic filler ~
inside the particle accelerates the net diffusion of phenol into -the bead, thus further promoting the oxidation.
In this manner, using either a filled or unfilled gelled metal alginate particle which has been stained with a sensitizing dye, it is possible to effectively promote the photooxidation of organic wastes including aromatics like cresol and phenol. This may be done in a batch or a continuous process ' :, - 8 - ;

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Accordingly, it is an o~ject of the present invention to provide an effective method of promoting photooxidative destruction of organic wastes using dye-stained, gelled, metal '~' alginate particles. ' '~' '-It is another object of the present invention to pro- -: -vide dye-stained, gelled, metal alginate particles containing a basic filler which particles may be used to provide an alkalinè
condition favorable to the oxidation.
Other o~jects and advantages of the present invention will be apparent from the following description and the appended claims.
Description of the Preferred Embodimenks The present invention for promoting photooxidative destruction of orgainic wastes was tested primarily for its effectiveness-in oxidation of phenols because of their outstand- ' ing environmental impact.' Photochemical oxidation does not oxidize phenols completely to carbon dioxide and water, but does destroy the aromatic ring system which is primarily res-~ sponsible for toxicity. The products that do form are probably "' ;~ susceptible to further photooxidation, hydrolysis,and biode~
gradation. There~ore, it is possible that photooxidation could be used as a step pre'liminary to biodegradation in the usual manner, whereby the toxicity of phenols to microorganisms is obviated.
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Although the photosensitized oxidation of phenols by dye sensitizers i5 generally considered to proceed by a ~
mechanism i'nvolving singlet oxygén generation, other mechanisms '' "' are-known for photosensitized oxidation in general~ and these may occur instead of,'or in addition to, the singlet oxygen mechanism. Any oxidation which is promoted by dye sensitization, '~

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whether through production o~ $inglet oxygen or otherwise is a possible react~on to ~e promoted by the stained alginate particles of t~e present invent~on. T~us, dye sensitizers can also be used to promote the photooxidation of aliphatic amines, mercaptans, olefins, and certain heterocyclic compounds, any of -which may be present as pollutants in industrial effluents. The use of these dye sensitizers bound to the particulate alginate material as in the present invention is often desirable in such photosensitized oxidation reaction, and thus, it i5 possible to use the disclosed process;for the treatment of numerous types of waste effluents in addition to phenolic wastes.
A dye which promotes photochemical oxidation without being consumed by the reactlon is considered a sensitizer~. Its activity may be through a mechanism in which the dye adsorbs visible light energy, transfers it to another compound such as dissolved oxygen, thereby returning to ground state to adsorb more light, or one involving the`transfer of electrons. In the present invention, the dyes that stain the gelled alginate -particles deeply and are retained well are those with marked ;
aggregating or metachromatic properties. Cationic dyes without these properties adsorb to the bead by ion exchange but easily wash out. Fortunately most of the strongly photosensitizing dyes happen to fall into the former category. ~
Staining has been carried out with dyes of the acridine, ~ ~ -thiazine, triphenylmethane, phenazine and phthalocyanine classes of dyes, although the thiazine dyes are preferred since they are often the strongest sensitizers. Aluminum alginate particles bind dyes like thlonine normally, but also bind dyes of classes that are known~to be ligands for the Al~3 ion. These classes include the alizarins and hypericin.
Usually the dyes in an aqueous solution form are used to stain the gelled alginate par~icles. Any concentration dye , . .
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may be used, but those in the 10 4 to 10 3M ran~e are pre~erred.
Likewise, the amount of d~e bound to the partl`cles may vary greatly, ~ut generally the dye to alginate normality ratios used ranged from 1:30 to 1:200. Dyes which are not soluble in water may be applied from an organic solvent solution and then the stained particles transferred to water. For example, the dye chloroaluminum chlorophthalocyanine was put on gelled barium alginate beads in methanol solution and the beads then placed in water.
The gelled alginate particles may be prepared by adding a solution of an alginate (such as sodium alginate) drop-wise to a solution of a divalent; or trivalent metal salt (such as 0.03 M Ba(NO3)2, O.lM CaC12 or O.lM Sr (OOCCH3)2) under gentle stirring. The concentration of alginate solution is not critical to the size of the particle for~ed, but does affect somewhat its mechanical strength and capacity ~or stain. Gelled particles have been made with from 7.5 X 10 3 N (1.5 g/l) alginate solution to 4.2 X 10 2 N (8.5 g/l) alginate solution, that is up to a 1% solution. Mechanical consistency o~ the bead sets ~o the lower limit on concentration of alginate solution; viscosity `~ sets the upper.
As each drop of alginate solution contacts the metal salt solution, a pellicle of gel form~. It then becomes i ~-uniformly gelled as the ions permeate it. The drop shrinks `~
to about one-third of its original volume and becomes a weakl~
elastic, so~t, easily cut, transparent particle or bead. Al-.. . .
though the beads are deformable, they do not crumble under normal careful handling.
In addition to the barium, calcium and strontium salt .
gelling solutions mentioned, lead, iron and copper ones have beén used in a like manner to gell sodium alginate drops. At least 10 3 moIar solutions are used, with the saturation point , , " ~ , ,, : , ~ . ;
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As mentioned, an alternatl~e means of obtaining a particular metal alginate is to use an ion-exchange process on already gelled alginate particles. Thus, aluminum alginate beads have been made successfully by treating calcium alginate beads with alum solutions.
Beads are separated from supernatant by decantation or draining through a Buchner funnel. They shrink through syneresis if left out of water very long, and so must be kept immersed.
Similarly, they are not stable in strongly alkaline solution' because of hydrolysis, or in solutions containing acids, mono- ~ -valent salts at high concentration, or certain chelating agents ~ ' because of displacement of the divalent metal binding the gel. ~ -If such conditions are encountered in application, chemical modification of the beads to withstand these conditions should ' be used. ;
As mentioned, one method of creating a weakly alkaline condition, which favors photooxidation of phenols, is by use of basic fillers within the gelled alginate particles themselves.
This is easily accomplished by milling the basic materials, ~ ~
such as MgO, MgCO3 CaCO3, SrCO3 BaCO3 or mixtures, into the ' - alginate solution before forming'the gelled particles. While , various amounts may be used,'the preferred ràtio of salt addition ' is lg per 25 ml of alginate solution'. ' ~' A number of examples follow which illustrate the use of stained alginate gel particles in the photosensitized '' oxidation of typical pollutant phenols. Most of these reactions -~; ~ were run in the laboratory in a batch-type readtor, with artifical ~tungsten) lighting, and with oxygen introduced into '30 the system. Reactions have also been fol~owed in open vessels, exposed to the atmosphere and sunlight. Because of the greater intensity of sunlight, these reactions appear generally to go more rapidly and thoroughly than the former.
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Some degree of photosensitized oxidation has been observed with most of the d~es used of the classes mentioned, but the most effective dyes readily available were found to be those of the thiazine class, including Methylene Blue, Thionine, and Toluidine Blue. One of the more effective filled bead systems, barium alginate plus barium carbonate, was used routinely with Toluidine Blue to compare the behavior of different phenols.
ExAMæLE I
Sl:rontium alginate gel beads were prepared by adding 25 ml of 8.6 X 10 3 N sodium alginate (Manugel, Alginate -Industries Ltd.) dropwise ko 500 ml of 0.1 M strontium acetate -solution. The beads were drained, treated with 50 ml of ~
2r x 10 4 M strontium acetate, and with distilled water. They ~ -were then stained with 5.5 x 10 6 moles of Toluidine Blue, so that the ratio of alginate uronic acid residues to dye molecules was 39. -~
These beads were added in a round bottom flask to `~
800 ml of a solution containing 1.025 x 10 3 M phenol and 10 ml of saturated strontium hydroxide solution, and irradiated with ~20 a 750 watt-projector lamp 22 cm from the reaction flask. The flask was kept at approximately 23 by a water bath, and a slow stream of oxygen was ~ed into it. The contents were stirred magnetically to keep the beads circulating through the solution.
Irradiation was continued for 23 hours during which , .
~ ~ time 13 ml more saturated strontium hydroxide was added to ;~ maintain the phenol in an ionized state. The light intensity measured in back of the reactor was 1.25 x 105 erg/cm2sec.
The solution soon turned olive-brown, and the absorp-~ ~ tion speckrum correspondingly showed continuously increasing ;~30 intensity throughout the visible and ultraviolet regions, belong-- ing to oxidation products of phenol. The lack of charact-eriskic bands in the spectrum of these products indicated that ' ~, '. ! ',, . i 10554~0 the aromatic ring system of phenol ~as being destroyed. Analysis of the ultraviolet spectrum showed that about 50% of the phenol had been ox.idized in 23 hours.
Chemical oxygen ~emand (COD) measurements were made with a Precision AquaRator. These showed a reduction from 236 ppm at the beginning to 148 ppm at the time the reaction was stopped. -EXAMPLE II
Barium alginate gel beads containing magnesium carbonate were prepared by adding 25 ml of a 1~ solution of sodium alginate (sample obtained from Xelco Co.), combined with 1 g of freshly precipitated magnesium carbonate, dropwise into 500 ml of 0.05 M
barium nitrate solution. On standing in wash water, the beads began to swell because of replacement of barium in the gel cross- -links by magneslum, but this was suppressed by transferring the beads to 10 3 M barium chloride solution.
The beads were washed twice and stained with 5 x 10 6 moles of Toluidine Blue. The ratio of polyuronic acid equivalents to moles of dye was 215. ~
The stained beads were added in a round bottom flask ;~-Zo to 800 ml of 1.15 x 10 M guaiacol, without addition of external ; base, and the reaction conducted for 23 hours as in Example I.
Under irradiation, the solution darkened rapidly, with ~steadily rising absorption in the visible and ultraviolet regions. Analysis of the ultraviolet spectrum showed that the ~ ~ .
~bands of guaiacol wer,e essentially gone after four hours, b~ing replaced by the broader band of a nonaromatic product. This band too was gone after 23 hours, leaving only continuous absorption. Meanwhile, the beads were bleached, though some dye ~- was~detectable in solution.
The COD fell from 310 ppm at the beginning of the reaction to 138 ppm at the end. After the reaction, alum was added to the solution, whereupon a brown precipitate separated ;. .. , ,. .'. . , , ' .. ' , ' . . . , . . . . . ., ~ .:

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and the COD o~ the supernatant fell to 90 ppm.
EXAMPLE III
Calcium alginate gel ~eads containing dolomite were prepared by adding 25 ml of 1% sodium alginate (Kelco sample) solution, mixed with 0.9 g dolomite (ca. 2CaCO3 MgCO3), drop-wise to 150 ml of 0.1 M calcium chloride solution. These beads were used in two reactions, recovered each time, and restained ~- -a third time with 5 x 10 6 moles of Toluidine Blue. The beads ;~
were added in a round bottom flask to 800 ml of solution, ~ ~
1.015 x 10 3 M in p-cresol, and irradiated as before for a -; -total of 47 hours.
The reaction proceeded without marked discoloration of the contents of the flask, but there was a strong increase of absorption in the shorter ultraviolet. Cresol was destroyed at the rate of about 6% of the remaining cresol per hour. After ~ -47 hours, there was estimated to be no more than about 6~ of the original cresol left. On a weight basis, this amounts to a drop from 112 ppm to 6.6 ppm cresol. -Although this reaction went somewhat slower than when barium or magnesium carbonate is used as a basic filler, the pH of the solution did not become alkaline at any time, as evident from the appearance of the spectrum of cresol. The buildup of visible-absorbing oxidation products was markedly less than in other runs.
EXAMPLE IV
Filled and stained barium alginate gel beads were prepared from 25 ml of 1~ sodium alginate solution (Kelco sample), 1/3 g. of barium carbonate, and 5 x 10 6 moles of Toluidine Blue, as in previous examples. These beads were used in a round bottom flask to oxidize 0.0514 g of p-chlorophenol in 800 ml of water (5 x 10 M). Irradiation was continued for 95 hours.
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10554;20 ~ bsorption due to products rose continually through the vîsi~le spectral region and t~e ultra~iolet above 290 nm.
Below that wavelength, backgrolmd a~sorption decreased after three days. Absorption bands of a definite product appeared -around 250 nm, maximized after about seven hours irradiation, and had vanished at the end of the reaction. In contrast, bands in the region characteristic of p-chlorophenol persisted until the end of the reaction, in an amount about 22~ of the original chlorophenol absorption.
Analysis of the ~inal solutions with 3-methyl-2-benzothiazolinone hydrazone indicated the presence of a phenol, but apparently non p-chlorophenol. It is possible that a pro-duct of the reaction is a phenol which is refractory to further oxidation, perhaps because of a high acid dissociation constant.
The COD fell from 112 ppm at the beginning to 42 ppm at the end, and addition of alum did not decrease it further.
Titration of chloride showed that 73% of that originally in chlorophenol had been released in inorganic form by the oxidation.
In oxidation of more dilute p-chlorophenol solutions (10 4M), destruction of 95% of the starting material could be"
obtained. In an oxidation of 2 x 10 4M, 2,4-di-chlorophenol sensitized hy thionine, 94% loss of the phenol was reached after twenty-four hours.
EXAMPLE V
Strontium alginate gel beads, made from 25 ml of sodium alginate solution, 7.5 x 10 3N, and containing 0.73 g of strontium carbonate, were stained with 5 x 10 6 moles of Toluidine Blue. These were added in a round bottom flask to 800 ml of a solution saturated in pentachlorophenol (10 4M), and oxidation sensitized as usual.
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The pentachlorophenol appeared entirel~ gone a~ter four hours, its place ~eing ta~en b~ a product absorbing at somewhat shor~er wavelengths. This product, too, was nearly gone - ~-after six hours, and after twenty~three hours only broad bands of products in the shorter ultraviolet remained. There was thus evidently complete oxidation of pentachlorophenol to non- ;i-aromatic products in that time.
2,4,6-trichlorophenol and 2, 3, 4, 6-tetrachlorophenol were oxidized in a manner similar to this.
EXAMPLE VI
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Barium alginate gel beads were made by dropping 85 ml of a 1% sodium alginate solution into 500 ml of 0.04 M barium nitrate solution, and allowed to stand until they had shrunk to constant volume which is from 1/4 to 1/3 of the original volume of alginate solution. The beads were then poured into a glass column 48 cm long by 1.2 cm diameter. The column contained 3.6 x 10 3 equivalents of uronate residues.
The column of beads was stained by drawing 10 3 M
thionine solution into it, until 3.6 x 10 5 moles of dye had ~20 ~ been attached to the beads, giving a polymer equivalent-to dye ratio of-100. The dye was taken up very rapidly, and the beads ;~-appeared purplish-black.
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~ The column was held in an enclosure with three 15-watt ~ ~ .
fluorescent lamps parallel to it. Inside walls of the enclosure were painted white ~or better reflection of light.
Water was poured through the column until the con-, ; ~ centration of dye in the effluent fell to 1 x 10 6 M. The color of dye in water in equilibrium with the beads was barely dis-~cernible.
~30~ A solution, 1 x 10 4 M in phenol and 2 x 10 4 M in tetraethylammonium hydroxide (pH 8.9), and saturated with oxygen (ca. 1.25 ~ 10 3 M), was then introduced into the column.
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When the concentration o~ phenol in t~e ef1uent reached its maximum ~alue, tAe l;`ght was turned on. The phenol solutîon was passed through t~e column at different flow rates, and the ultraviolet spectrum of the effluent recorded at frequent in-tervals.
At a flow rate of 60 ml/hour, phenol was not detectable in the spectrum of ~he effluent, the dominant product being one with an absorption band at 245 nm. At faster flow rates, phenol appeared in the effluent, but at slower flow rates to 30 ml/hour, the 245 nm product was itself almost eliminate~, leaving generally ~ -rising absorption through the ultravislet in indistinct bands.
A total of 1 liter of phenol solution was passed through the column. -After this, 1 liter of 10 4 M p-cresol, and 1 liter of ~
10 4 M p-chlorophenol, were passed similarly through the column, ~ -; with similar results overall. During this time, the dye was not leached from the beads to such an exten~ that replenishment was necessary.
' ~; Higher concentrations of phenols were not used because ~20 of the limited solubility of oxygen in water. Under these conditions, formation of products with absorption in the visible ~ , .
region was not evident.

Unfilled gelled alginate particles are better for :::
such column applications as found in Example VI above and in other situations where the volume created is restricted. They keep the dye better and dissolution of the filler would not limit ~ .
their useful life. Therefore alkali material such as lime water s also metered into the column while processing the organic wasteO
Filled particles are generally preferred for broadcast application and situations where ponds, lagoons or natural waters are treat~d since it is not feasible to add alkali materials :

, ~' ' ' . . .. . . .. . .. . . . . . . . .

iO554;20 under those conditions. Of couxse, i~ t~e waters to be treated are naturally alkaline, unfilled gelled alginate particles could be used. In the application to ponds, lagoons, etc., it is contemplated that this can be a one-time application with the stained gelled alginate particles biodegrading rather than being recovered.
From the foregoing examples, it can be seen that the dye-stained, gelled alginate particles of the present invention are useful in promoting the photooxidation of various phenols found in waste effluen~ts. They are also useful in promoting the photoxidative déstruction of other organic wastes found in aqueous effluents. Similarly, it is believed apparent to one of ordinary skil~ in the art that the same particles could be used to prepare a desired oxidation product of an organic or inorganic compound, if that desired product can be prepared by photosensitized oxidation. By this means then, industrial chemicals could be commercially synthesized and produced in the ~; same manner that industrial waste effluents can be photo- -~ ......
~oxidatively destroyed. -20 ~ While the method herein described constitutes a pre-ferred embodiment of the invention, it is to be understood that the invention is not llmited to this precise method, and that changes may be made therein without departing from the scope of the invention.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A method for photooxidative destruction of organic wastes found in aqueous effluents utilizing a dye sensitizer to promote the oxidation of said organic wastes by air or oxygen in the presence of visible light, at an at least weakly alkaline pH and under other process conditions operable to effect the photooxidation wherein the improvement comprises using as the promoter biodegradable, gelled metal alginate particles selected from the group consisting of barium alginate, calcium alginate, strontium alginate, and aluminum alginate beads which have been stained with a dye sensitizer selected from the group consisting of the acridine, thiazine, triphenylmethane, phenazine, phthalocyanine classes of cationic dyes, the dye to alginate normality ratio being in the range of

1:30 to 1:200.

The method of claim 1 wherein said beads are prepared by adding a solution of sodium alginate to a solution of divalent metal salt selected from the group consisting of barium, calcium and strontium salts to form a gelled bead.

The method of claim 1 wherein said beads are prepared by treating calcium alginate beads with alum solution.

The method of claim 1 wherein thiazine dyes are used.

The method of claim 1 wherein said organic wastes include phenolic compounds and said photooxidation takes place under weakly alkaline conditions.

The method of claim 5 wherein said alginate particles contain an alkaline salt filler material to provide at least a portion of said alkaline conditions.

The method of claim 6 wherein said filler is selected from the group consisting of magnesium oxide, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate and mixtures thereof.

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The method of claims 5 wherein said alginate particles are gelled beads selected from the group con-sisting of barium alginate, calcium alginate, strontium alginate and aluminum alginate beads and said sensitizing dye is a thiazine dye.