AU626571B2 - Biodegradation of oxalate ions in aqueous solution - Google Patents

Description

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AUSTRALIA

Patents Act 6win MW COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority 0 0 Related Art: 0 r 0O q Aplicant(s): Alcan International Limited 1188 Sherbrooke Street West, Address for Service is: Montreal, Quebec, H3A 3G2, CANADA

I

Sr, 0 0 PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA ,"'Complete Specification for the invention entitled: BIODEGRADATION OF OXALATE IONS IN AQUEOUS SOLUTION Our Ref 143640 POF Code: 1649/1086 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 6006 4 Li;; -I CI--iea~UbpCIEI1PIT~rL~ijr i

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BIODEGRADATION OF OXALATE IONS IN AOUEOUS SOLUTION FIELD OF THE INVENTION This invention relates to methods and biological cultures useful in the biodegradation of oxalates removed from a Bayer processing system which produces aluminum oxides.

BACKGROUND OF THE INVENTION A common problem in the processing of mineral ores, 10 particularly in the processing of bauxite by the Bayer 0 4 o °process, for the production of alumina is the generation o 0 and accumulation of oxalate ions commonly referred to as oxalates in the Bayer processing streams and waste 0040 r streams. Environmental concerns may prevent the dumping O 0 o So 15 of oxalates at disposal sites. In view of the S0 appreciable quantities of oxalate solids which have to be removed from the Bayer process, which may range from one to ten tons daily in a typical medium-sized Bayer processing plant, the use of large scale disposal o o 20 systems are required. For example, the solid oxalates So with or without liming may be buried in red mud from the Bayer processing system. The oxalates could also be °00 0burned in a kiln, such as a lime kiln; however, these i procedures are by and large prohibitively expensive.

As is generally understood, bauxites by and large o ocontain low percentages, usually less than 0.5% of organic matter mostly in the form of humates. In the Bayer processing system, the humates, which dissolve in the process liquors, are ultimately degraded to acetates, formates, carbonates and oxalates. These compounds tend to concentrate as their sodium salts in the processing liquors. Most of these sodium salts have relatively high solubilities in the processing liquors and as such do not interfere with the process. However, sodium oxalates have a relatively low solubility and readily precipitate out of the processing liquors l i 2 particularly in portions of the processing system which operate at cooler temperatures and higher caustic soda concentrations. As the oxalates precipitate out of the processing solution, restrictions in the processing system result which can considerably reduce the effectiveness of the overall processing operation.

Furthermore, the build-up of oxalates in the processing liquors tends to cause a reduction in alumina trihydrate yield from the process and ultimately a co-precipitation of the sodium oxalate with the alumina trihydrate. When I .the alumina trihydrate is contaminated with oxalates, it o has been found that calcination of the precipitate fl#0 eoo results in a very weak and fine alumina which leads to excessive dust losses in the subsequent calcination step o 99j o o 15 and production of aluminum by electrolysis. Hence it is eq s 0 very important to keep the concentration of oxalate levels in the Bayer processing system below some critical value to avoid these problems. Although it is possible and is routinely done in many areas to remove 20 oxalates from the processing system by drawing off a o0o portion of the liquors, or by precipitating out and 0 0,0 removing solid sodium oxalate, the above noted '0 alternatives in the ultimate disposal of the oxalates are becoming commercially prohibitive.

25 In accordance with this invention, a microbial 090d degradation of oxalate ions in a stream discharged from the Bayer processing system is provided. Although the scientific literature discloses that microorganisms are known to assimilate and then metabolize oxalic acid or oxalate ions as a carbon source, it has never been contemplated that microorganisms could be used to degrade the oxalates in processing liquors of a Bayer processing system, because of the extreme toxic nature of such liquors. However, according to this invention, a method is provided which surprisingly does result in p an effective economically attractive biodegradation of oxalates from the waste stream on a continuous basis.

SUMMARY OF THE INVENTION In accordance with an aspect of the invention, a method for the biodegradation of oxalates in solution which have been removed from a Bayer processing system which produces aluminum oxides is provided. The method comprises removing a water soluble oxalate containing composition from a processing stream of the Bayer process. Microorganisms for degrading oxalates are maintained in a bioreactor. The oxalate-containing o composition is treated in preparation for introduction to a bioreactor including redissolution in water, if necessary, and adjusting pH of the solution to be compatible with the microorganisms in the medium. T'ie treated oxalate containing preparation is introduced to the bioreactor, wherein the oxalates are biodegraded and, as needed, a portion of the preparation is removed.

According to another aspect of the invention, .00 20 microorganisms are developed in the bioreactor by Sooo acclimatizing selected microorganisms capable of assimilating and metabolizing oxalates to degrade the 0 0° oxalate in the solution derived from the composition removed from the Bayer processing system. Preferably the microorganisms are derived from rhizosphere soils.

o0°: BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be discussed with respect to the processing system in the drawings wherein: Figure 1 is a simplified Bayer process flow diagram; Figure 2 is one embodiment in processing the oxalate containing liquors removed from the Bayer processing system; and Figure 3 is an alternative embodiment in processing v -1 i ~ii ii 4 oxalate containing liquors removed from the Bayer processing system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As is understood by those skilled in the art, the Bayer processing system comprises a series of processing steps for treating bauxite to yield alumina normally in the form of purified aluminum trihydroxide, which is then calcined to aluminum oxide. Vast quantities of bauxite are treated on a daily basis; hence it is necessary to recirculate processing liquors containing o" caustic soda to economize on reagent used in the process 0 for digesting the bauxite.

In the Bayer process, bauxite ore is mixed with .ao caustic liquor and treated ("digested") under conditions o 15 of elevated temperature and pressure to dissolve the So aluminum oxide values in the ore as sodium aluminate.

After digestion, the hot liquor or slurry, carrying insoluble material ("red mud") and dissolved sodium aluminate, is cooled, and the red mud is separated from

OOOC

°0 o 20 the liquid of the slurry; the liquid, containing the 0o dissolved sodium aluminate, commonly referred to as pregnant liquor, is then cooled further and treated (as °oo by seeding with aluminum hydroxide and stirring) to precipitate aluminum hydroxide. The coarsest part of this precipitate is separated out, washed and ultimately calcined to obtain alumina as the end product, and the fine part is redirected as seed, while the remaining liquid ("spent liquor") is recycled, possibly evaporated and regenerated with addition of caustic, and heated to treat fresh quantities of bauxite.

With reference to Figure 1, a block diagram is provided to outline in a simplified manner the Bayer process flow diagram and to exemplify recirculation of the treatment liquors. In the following discussion, it is generally understood that reference to composition means streams, either of solids, liquids, or slurries i f originating in the Bayer process. The term "preparation" means oxalate from the compositions that has been made free of excess Na ion, dissolved in aqueous fluid, and whose pH has been adjusted to approach neutrality. The term "medium" refers to the nutrient solution containing the essential N, Mg, Fe and P required for growth.

Mined bauxite is wet ground at step or stage 10 to pulverize the bauxite to a suitable particle size. The resulting bauxite slurry is optionally heated in system o° 12 by the introduction of steam. The heated slurry is 0 then optionally held for predesilication in holding tanks 14, typically for sixteen hours at 80°C to The bauxite ore is then digested and desilication is 0 15 continued in the pressure digesters 16 with the So introduction of steam. Treatment continues typically for approximately thirty to sixty minutes at 135°C to 150'C for gibbsitic bauxites, or 220°C to 260°C for boehmeitic bauxites. Flash cooling of the solution is 0004 0 20 provided for at 18 with transfer of flashed steam via 000 0line 20 to the heaters 22. The process liquors 6 .4 containing the dissolved alumina hydrate are processed 00oO after being cooled to just below the atmospheric boiling temperature in the red mud separation system 24. The red mud solids are transferred to mud washing system 26 where the red mud is washed and finally discarded at 28.

Fresh water is introduced to the mud washing system which is returned to red mud separation unit 24 carrying the recovered soluble values into the main process circuit. The separated liquid from the separator 24 is passed on to the polish filtration system 30. The solids removed in polish filtration are passed on to the mud washing unit 26 via line 34. The polished processing liquors are in turn passed on to systems for further cooling, precipitation of pure aluminum I hydroxide and classifying the precipitate, shown as 32.

:4 o P* 042 42 p1p 0 o 424 Pl 024 0 pp Ga 4 Ct PC 4242 p 42 4 P42424 p o p 42 42 p" pp Op 4 42 42* 42 2 4 42 4242 424424 The purified product in the form of alumina trihydrate, or aluminum trihydroxide, is removed from system 32 via line 36 and is subsequently washed and calcined to a suitable form of aluminum oxide. The remaining spent processing liquors are transferred via line 38 optionally to the evaporator 40. Steam is introduced to the evaporator 40 to drive off water in line 42. The remaining reconcentrated spent processing liquors are passed through heater 22 for return via line 50 to the digestion system 16 and to the bauxite grinding system 10 via line 52. Make-up caustic to compensate for caustic losses is added at this point.

From this brief outline of the Bayer processing system, it is apparent that the processing liquors, as 15 removed from the classifying system 32, are recirculated either to the desilication system 16 or the bauxite grinding system 10. As the processing liquors continue to recirculate through the system, the oxalate concentration normally in the form of sodium oxalate 20 continues to increase. As already noted at cooler points in the process, the oxalate may crystallize and thereby constrict flow and efficiency of the system, poison the precipitation step, or lead to other process problems.

It is therefore necessary to provide some means for separating oxalate ions from the liquor and removing them, typically as sodium oxalate, from the Bayer liquor circuit to avoid such problems.

Various schemes have been proposed for the removal of oxalate from the main liquor circuit. For instance, the fine aluminum trihydroxide recirculated as seed material in the precipitation step 32 may contain precipitated sodium oxalate, since this is the coolest point in the process and the solubility of sodium oxalate in Bayer liquor decreases markedly with temperature. In such cases, the fine aluminum i- 7 trihydroxide seed may be filtered to remove most of the spent Bayer liquor, washed with cold water to displace residual spent liquor in the filter cake, and then washed with very hot water to dissolve the sodium oxalate. This hot wash solution then contains a relatively high dissolved sodium oxalate content with relati'vely little caustic soda in solution, and can be removed from the process as stream 48.

Alternatively, a part or all of the liquor product from the evaporator 40 may be cooled and passed over a suitable packing in a column, whereupon a part of sodium 9 oxalate in supersaturated solution will precipitate in solid form on the packing, as outlined in Assignee's United States patent 4,038,039, or Canadian patent 1,066,482. From time to time, the accumulated sodium q oxalate in the packed column is removed as sodium oxalate solution by washing the column with hot water, again providing a sodium oxalate solution low in caustic soda which can be removed from the process stream 46.

As still another alternative, a part of the product o°o liquor from the evaporator 40 may be further concentrated by evaporation and suitably cooled to 99o9° crystallize out solid sodium oxalate (together, typically, with some sodium carbonate and other sodium impurity salts), which can then be separated as a solid waste product rich in sodium oxalate by centrifugation, filtration or the like. This can then be removed from the process as solid sodium oxalate, etc., or i redissolved in water as a solution rich in sodium oxalate, as stream 44.

The problem then remains of how to dispose of the sodium oxalate removed from the main process stream as either a sodium oxalate-rich solution, or as solid sodium oxalate in an environmentally acceptable and economical manner. As noted earlier, the known disposal methods (burial, formation of insoluble calcium oxalate S8 by reaction with lime, burning, etc.) all have serious cost and/or environmental drawbacks.

In accordance with this invention, a microbial treatment system is provided for treating the compositions in the form of liquors as removed at points 44, 46 or 48 to free the liquors of oxalates before optionally returning soluble values to the Bayer processing system. With reference to Figure 2, a first embodiment of the invention is illustrated in block diagram form. The concentrated liquors, as extracted from the evaporator in line 44, are separated at step 54 which separates out the precipitated oxalates and returns the filtrate liquor via line 56 to the Bayer processing circuit. The solids are washed at step 58 by cold recycled medium indicated by line 60 which is removed from the bioreactor stage 62. The cold recycled medium has the biomass removed therefrom by the separator 63. The solids from separator 63 are normally discarded. The separated liquid from the separator 63 0090 0 20 is then used as the wash liquid. The wash solution, as 000 it emerges from the separation step 58, is transferred back to the Bayer processing system as indicated by 0 o9arrow 64 for recirculation in the treatment liquors.

The washed solid sodium oxalate is dissolved at step 66 in hot water introduced in line 68. Alternatively, tilt this solution could be produced by the washing of oxalate-containing fine alumina trihydrate seed, as outlined earlier. The pH of the solution is adjusted preferably to the neutral range by the addition of a suitable acid component. In addition, it may be necessary to adjust the concentration of Na+ ions in the solution to a level which can be tolerated by the microorganism developed to digest the oxalates. The concentration of Na+, should adjustment be required, may be accomplished by dilution of the liquors. Preferably the Na+ concentration should be adjusted below a level Viit 4 I_~Y)1 il-^ i-lild~u--_14il-ill~L:.i~--l -~.IIJFY~IL---C I.T-C .I I- LI-IIXI-- ^r:il*l-liilr--l(l l 00 0 100 a 00 0 064 00 0 0d 0 0 0 0 000d 00 00 of approximately 8000 mg/L. Optionally nutrients may be added to the composition before introduction to the bioreactor 62. The nutrients are selected so as to provide the necessary phosphate, nitrogen, iron and magnesium. The above nutrients are added as various salts and optionally yeast extract, as noted subsequently, for the bacterial population in the bioreactor. The source of carbon for growth of the microorganisms is provided by the oxalate. The treated composition to form the preparation is introduced via line 70 to the bioreactor step 62. The bioreactor is of a construction to provide for digestion of the oxalate by virtue of a suitable residence time in the biocontactor. Preferably the residence time for the introduced composition in the reactor is in the range of 5 hours.

The operation of the oxalate biodegradation system is normally on a continuous basis. The volume of the reactor used in step 62 is therefore chosen to provide 20 the desired average residence time. The portion of medium returned via line 60 as removed from outlet line 72, is sufficient to provide the necessary liquid, which is first clarified to remove solids, for example, by treatment with alum, to wash the incoming solids. Any excess medium, now of very low oxalate content, can be disposed of with the red mud or returned to the Bayer process as wash water. Normally the expended wash waters of line 64 are returned to the Bayer processing system. This removes most of the caustic soda in the filter cake of the wash step 58. The filtrate normally therefore contains the caustic soda, sodium carbonate, sodium sulfates and other compounds which were originally occluded in the filter cake.

The bioreactor stage 62 is preferably carried out in a rotary biocontactor system comprising a plurality of discs which are rotatably mounted in the reactor.

0t 00 000 r r~ -rlrur:i~,sc~~- i -i r )I 4 0 40 -444 4 4I 04~4 The discs are partially immersed in the medium to the extent that, when they are rotated, a desired ratio of time that the discs are in the medium and out of the medium as exposed to air, is preferably in the range from 0.5 to 0.5 to 0.1 to 0.9.

The concentration of the oxalate, expressed as

C

2 04 in the composition prior to introduction to the rotary biocontactor may be up to 7,000 mg/liter. The composition may optionally include nutrients of the type set out in the Examples, or chemical equivalents thereof. The pH of the composition is adjusted to close to neutral by use of a suitable acid, such as sulfuric acid. Under suitable operating conditions, the residence time in the reactor can be as low as four to 15 five hours to achieve 99% removal of the oxalate in the feed. The normal operating temperatures of the reactor may be in the range of 5°C up to 40°C. Sufficient air is always present in the reactor to provide an aerobic environment above the medium in the reactor for degrading of the oxalates in the system as the microorganisms grow and assimilate oxalate and metabolize it to produce biomass or CO 2 and H 2 0. This results in discharge in the line 72, which is very low (below the limit of detection of the assay method, which is estimated to be 50 mg/L) in oxalate, and, as mentioned, the majority of which is recycled to the Bayer processing system. The balance may be discharged or used for other purposes in make-up in the Bayer processing system.

When the oxalate is removed, by the Assignee's patented procedure patent 4,038,039) using an oxalate column (line 46 in Figure they are treated slightly differently before introduction to the bioreactor system. With reference to Figure 3, the oxalate containing solutions are introduced to the oxalate removal column indicated at step 74 which cools i j.

r ~a I :i 11 the solution down to precipitate out the oxalates on the column packing. Periodically, the same column is transferred to a washing mode and the cold water washing system step 78 is first used to remove excess liquor from the column. The treated liquors removed from the column at step 74 are transferred via line 80 back to the Bayer processing system as well as the cold wash in line 82. The cold water wash is optionally provided from the stored liquids in tank 84 which has been extracted indirectly from the discharged preparation in Vo 0 aline 86. A portion of the preparation is taken off in D 1line 88 and passed through the filter system 90 to remove the biomass from the preparation which is discharged via line 92. The separated liquid is transferred via line 94 to the storage tank 84. It is 0° appreciated that oxalates should provide the major source of carbon for the microorganism to effect biodegradation of the oxalates. It is therefore preferred to discard the separated biomass rather than o 4 20 recycling to the bioreactor, because the separated oo biomass could act as an alternate source of carbon for the microorganism and detract from degradation of 6o oxalates.

In the next part of the periodic column washing operation, the same column is placed in the hot washing o o6 mode 98 and washed with hot water which dissolves the oxalates to provide an oxalate solution which is stored in a tank at step 100 via line 102. The medium is _adjusted in pH and nutrients optionally added before introduction to the reactor stage 104 as per line 106.

The reactor operates in the same manner as that described with respect to Figure 2 for degrading the oxalates in the incoming liquid composition to provide a discharge very low in oxalate concentration in line 86.

2 i

I

TiY-I- III-X 12 The preferred system for the biodegradation of oxalates in the processing of oxalate-containing side streams is to conduct the digestion in an aerobic environment. Although it is understood that anaerobic oxalate metabolizing organisms are also availble and would exist in the bioreactor, it was discovi :ed that a population of microorganisms could be developed in a bioreactor which degraded the oxalates in the processing stream in the aerobic environment. To develop the microbial population, it was discovered that isolation of microbial cultures from soil samples resulted in the ability to culture microorganisms which flourished in ao;* the presence of oxalates in the Bayer process side Sstreams. Hence the harsh environment of the processing oao 15 streams could be treated by this biological culture as established in the bioreactor.

Oxalate degrading organisms are most likely to be isolated from the rhizosphere of oxalate producing plants, some of which are identified in the following list: Dieffenbachia picta; (Dieffenbachia); Jatropha o .o podagrica; Monstera spp.; Philodendron spp.; Rheum Srhaponticum (Rhubarb).

*9 There are, of course, many microorganisms in the soil samples in which such plants grow which are capable of metabolizing oxalates. It is noted that the following microorganisms have such ability: Pseudomonas oxalaticus; Vibrio extorquens; Vibrio oxaliticus; Thiobacillus novellus; Pseudomonas spp; Alcaligenes spp; Spirillum spp; Streptomyces spp; Nocardia spp; Myrothecium verrucaria; Tilletia contraversa; Aspergillus niger; as well as cell lines from various types of mosses and barley roots.

The preferred microorganisms were isolated from the soil of the rhizospheres of the plants Dieffenbachia picta and Rheum rhaponticum. As is understood by those; skilled in the art, a variety of well known techniques 13 are available for isolating microorganisms from the soil. Such techniques are described in several readily available texts, such as, Frobisher, M. Fundamentals of Microbiology (1962), Chapter 38 Soil Microbiology.I., pp 502-503, W. B. Sanders Karavaiko, G.I. et al, Biogeotechnology of Metals: Manual (1988), Chapter 2 Methods of isolation, evaluation and studying of microorganisms, pp. 47-48, Centre for International Projects of the USSR State Committee for Science and Technology (GKNT), Moscow and Pelczar, M.J. and Reid, Microbiology (1958), Chapter 36 Soil Microbiology, p. 477, McGraw-Hill Book CompanyInc.

Cultures from soil samples of these plants produced a variety of microorganisms. Based on taxonomical 15 investigation, it is believed that the prominent O. microorganism which is capable of degrading oxalates is a Pseudomonas or Pseudomonas-like organism. The microorganism samples from the soils were acclimated to the processing liquors containing the oxalates. After 20 an extended period of stressing the microbial culture o, with the oxalate containing system, the desired 0 Pseudomonas or like microorganisms, capable of S.o assimilating and growing on the carbon source of the oxalate constituents in the harsh streams to be treated, flourished.

It has been found that the stressing techniques employed which lead to the efficient oxalate degradation by the developed microorganisms can be Scarried out in a continuous mode in a bioreactor.

Normally, the stressing of such microorganisms takes place on a batch basis as performed experimentally in shake flask cultures. The applicants have discovered, however, that exposure of the microorganisms to varying concentrations of oxalates in a continuous mode will result in a mixture of microorganisms capable of efficiently degrading oxalates. A suitable medium is 14 developed which includes the necessary nutrients, nitrogen, magnesium, iron and phosphorus and with a beginning concentration of oxalate C 2 0 4 at 3,000 mg/L.

Slowly over time, the concentration of oxalate, C204=, was increased to 5,000 mg/L; by approximately 2,000 mg/L oxalate to develop the oxalate metabolizing microorganisms. Under certain circumstances, it is possible to achieve concentrations of up to 7000 mg/L of C204 in the bioreactor which is metabolized by the active micororganisms. Preferably a four chamber rotary o, biological contactor is used. The discs of the biocontactor may be porous. The extent of immersion of the discs in the medium is adjusted so that the ratio of 'times that the discs are immersed in the liquid against 15 the time that the discs are exposed to air ranges from 0.5:0.5 to 0.1:0.9. The temperature in the biocontactor may range from 5°C to 40°C, but is preferably in the 25°C to 30°C range. Flow rate of the preparation through the contactor on a continuous basis is adjusted so that the average residence time in the o, contactor is, preferably, about five hours. The biocontactor is preferably subdivided, by means of 0o suitable internal dividers, to minimize bypassing of the 0 40 medium from the inlet to the outlet. Through the aerobic microbial degradation of the oxalates into :carbon dioxide and other biomass metabolites, there is the corresponding production of the biomass on the rotating plates of the rotary biocontactor. The effluent from the biocontactor has a very low concentration of oxalates and may be returned to the Bayer processing circuit after removal of the biomass.

The spent preparation may be used as a wash for the incoming oxalate solids.

The following Examples exemplify various preferred aspects of the invention.

EXAMPLE 1

S\

N

fl Reagent grade oxalic acid (H 2

C

2 0 4 .2H 2 containing essentially no impurities, was dissolved in an aqueous solution containing Na 2

HPO

4 .7H 2 0 0.5 g/L MgSO 4 .7H 2 0 0.1 g/L

(NH

4 2

SO

4 .7H 2 0 0.5 g/L Yeast Extract 0.1 g/L FeSO 4 .7H 2 0 0.05 g/L In addition, the biocontactor contained a microbial culture obtained from Rhubarb or Dieffenbachia rhizosphere soil.

The oxalate concentration in the medium, expressed as oxalate ion, C 2 0 4 was 3350 mg/L. The pH of the medium was adjusted to 7.0 by the addition of sulfuric acid.

The medium was pumped continuously through a 3 compartment rotary biological contactor. The rotating discs were made of non-porous Lucite, and had a total surface area of 3.7 m2., The liquid capacity of the contactor was 12 L. The speed of rotation of the discs was about 0.6 rpm, and disc immersion was such that the ratio of times discs immersed:discs in air was 0.5:0.5.

The temperature was maintained at 25°C. The residence time of the medium was 17.5 hours.

The concentration of oxalate in the three compartments was as follows: Influent 3350 mg/L 1st Chamber 1000 mg/L 2nd Chamber 500 mg/L 3rd Chamber 250 mg/L Effluent 100 mg/L This indicates that oxalate is indeed degraded by the microbial culture, at a residence time of 17.5 hours. However, the growth of biomass was uneven, most of the biomass was formed in the first chamber, with 16 very little in the second and third chambers, indicating that the residence time can be reduced.

EXAMPLE 2 The conditions were identical with Example 1, but the concentration of oxalate was 3550 mg/L, and the residence time was 5 hours.

The concentration of oxalate in the influent and in the three compartments was: Influent 3550 mg/L 1st Chamber 1650 mg/L 2nd Chamber 500 mg/L 3rd Chamber 150 mg/L Effluent 50 mg/L It was observed that at this shorter residence time, the amount of biomass in Chambers 2 and 3 had increased, and that oxalate degradation occurred throughout the contactor. A considerable amount of biomass was sloughed off the discs in the first chamber, however, new biomass was regenerated rapidly after 20 falling off.

EXAMPLES 3 TO In these tests, sodium oxalate filter cake from the Bayer process was used. This material is not pure, but contains sodium carbonate, sodium sulfate, iron and aluminum compounds, and small amounts of a large variety of organic carbon degradation products from humic compounds. In addition, the residence time was reduced to 5 hours.

The sodium oxalate was dissolved in a solution containing:

NH

4

H

2

PO

4 0.5 g/L MgSO 4 .7H 2 0 0.1 g/L Yeast Extract 0.1 g/L FeSO 4 .7H 2 0 0.05 g/L The biocontactor also contained a microbial culture obtained from Rhubarb or Dieffenbachia rhizosphere soil.

17 The pH was adjusted to 7.5 by the addition of sulfuric acid. The dissolved oxalate ion concentration in the solutions was: Example 3, 2600 mg/L; Example 4, 3200 mg/L; Example 5, 2450 mg/L.

The solution was continuously pumped through a 3-compartment rotary biological contactor. The 73 rotating discs were made of non- porous Lucite, total surface area 3.7 m 2 the liquid capacity was 12 L, the speed of rotation was about 0.6 rpm, and extent of disc immersion such that the ratio of times discs immersed:discs in air was 0.33:0.67. The temperature was maintained at 25 to The solution was continuously pumped through the three-compartment rotary biological contactor to give a 15 total residence time of 5 hours. The concentration of oxalate ion, expressed as C 2 04 mg/L, in each chamber of the contactor was measured for each of Examples 3, 4 and Example 3 4 20 Influent 2600 3200 2450 ist Chamber 1350 1300 1400 2nd Chamber 650 700 650 4 3rd Chamber 200 400 50 H Effluent <50 300 <50 These examples indicate that it is possible to obtain an almost complete degradation of the impure oxalate from the Bayer process, which contains a variety of degradation compounds from humic materials, within a residence time of 5 hours.

Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

if

Claims (12)

1. A method for the biodegradation of oxalate in solution which has been removed from a Bayer processing system for producing aluminum oxides, said method comprising removing an oxalate containing composition from a processing stream of said Bayer process, maintaining in «aibioreactor microorganisms capable of degrading oxalate, treating said oxalate containing composition in preparation for introduction to =asc t. bioreactor, including adjusting pH of said preparation to be compatible with said microorganisms in said o ao.c bioreactor and reducing sodium concentration to a level compatible with said microorganisms, introducing said o"o, 15 treated oxalate containing preparation to said a abioreactor wherein said oxalate is metabolized by said microorganisms, and discharging a portion of said preparation from said bioreactor. 20 2. A method of claim 1 wherein said oxalate Goo containing composition is continuously removed from said Bayer processing system and said preparation is i o continually discharged from said bioreactor.

3. A method of claim 2 wherein said discharged preparation has biomass separated therefrom and at least a portion of remaining liquid is continuously recycled to said bioreactor.

4. A method of claim 2 wherein sources of nutrients for said microorganisms are introduced to said preparation prior to introduction to said bioreactor. A method of claim 2 wherein said microorganisms are selected from the rhizosphere soil. 6iA -TrL! t -~E=lllf Ill--i-~lii~~ 19

6. A method of claim 5 wherein said microorganisms are selected from rhizosphere soil surrounding plants which produce oxalates, said plants being selected from the group of plants consisting of Dieffenbachia picta; Jatropha podagrica; Monstera spp.; Philodendron spp.; Rheum rhaponticum.

7. A method of claim 5 wherein said microorganisms are selected from rhizosphere soil surrounding the selected plants of Dieffenbachia picta and Rheum rhaponticum. 4 1

8. A method of claim 2 wherein said microorganisms are Pseudomonas or Pseudonomas-like. S o 9. A method of claim 1, wherein concentration of said oxalates in the form of C 2 0 4 in said preparation introduced to said bioreactor is in the range of up to 7,000 mg/L. A method of claim 9, wherein concentration of said oxalates in the form of C204 is in the range of 100 mg/L up to 7,000 mg/L. 11 A method of claim 2, wherein said oxalate containing composition is removed from said Bayer processing system as a solid in processing liquors, filtering solidified oxalates from said liquors and returning said liquors to said Bayer processing system to form a filter cake of solidified oxalates, washing said filter cake with said portion of said preparation removed from said bioreactor which is cold and has biomass separated therefrom, dissolving said washed oxalates in water to develop a concentration of oxalate ion in the range of up to 7,000 mg/L and adjusting the pH of said preparation to the neutral range to provide said treated oxalate preparation.

12. A method of claim 11 wherein Na+ ion concentration in said preparation is adjusted to be less than approximately 8000 mg/L.

13. A method of claim 11, wherein nutrients are added to said preparation, said nutrients providing sources of nitrogen, phosphorous, magnesium and iron. 0

14. A method of claim 13, wherein said nutrients 4 4 additionally comprise yeast extract. 4. 15 15. A method of claim 8 wherein said microbiological medium is developed with microorganisms isolated from sad44 soil samples and stressed with said oxalate containing preparation to acclimate said microorganisms to such influent and metabolize said oxalate, said microorganisms which survive such stress include Pseudomonas or Psuedomcnas-like microorganisms.

16. A method of claim 15 wherein said bioreactor is operated at a temperature ranging from 5°C up to 40 0 C.

17. A method of claim 15 wherein said bioreactor is a rotary biocontactor having a plurality of discs which are partially immersed in said preparation and on which said biomass grows, said discs being immersed in said preparation to an extent which provides a ratio of time discs are immersed in medium: time discs are exposed to air to be in the range of 0.5:0.5 and to 0.1:0.9.

18. A method of claim 8 wherein said group consists of Pseudomonas and Pseudomonas-like microorganisms. SLIDATED: 9 August 1989 -1 PHILLIPS ORMONDE FITZPATRICK Pate-b' t Attorn~gs fol, S2 I i L UW~f-: