temperature, and crystallized to produce purified terephthalic acid; each batch of such purification/crystallization produce a high strength wastewater with a chemical oxygen demand of about 20,000 mg/1, containing (terephthalic acid, benzoic acid, p-toluic acid, isophthalic acrid, etc., which is essentially a discontinuous waste stream.
Moreover, terephthalic acid, as well as aromatic acids having a similar structure - scull as, p-toluic acid, benzoic acid, etc. -have low solubility his water. Thus, the waste stream with significant amounts of! undisclosed components behaves like a slurry. The sparingly soluble substances may typically adhere to process equipments. To facilitate the washing of process equipments with adhered solids, certain amount of caustic lye (concentrated sodium hydroxide) may be used during the washing process to neutralize arid dissolve the sparingly soluble (weakly acidic) components. Hence the resultant wastewater may turn out to be alkaline. Over am, the wastewater emanating from the production facilities of PTA is likely to have several of the following features built in it:
(i) the wastewater may be acidic at times and may become extremely alkaline (i.e). , large fluctuations in effluent pH) , (ii) presence of a high concentration of sodium ions, and if neutralized with a mineral acid, high concentration of sodium salts such as sodium chloride,
(iii) presence of continuous and discontinuous streams with varying levels of COD and Biological Oxygen Demand (BOD) - hence large fluctuations in effluent flow rate and COD,

(iv) presence of sparingly soluble components such as aromatic acids,
(v) presence of highly water-soluble components like acetic acid, (vi) presence of aromatic hydrocarbons like p-xylene, and (vii) presence of metal ions such as cobalt and manganese. In view of the above factors regarding effluent generation, and the environment protection standards that should be complied with, the prime objective of this invention is to develop an efficient process to treat such waste streams that may contain significant quantities of sparingly soluble aromatic acids, and acetic acid, with other organic and inorganic components, while the waste stream may display wide variations in pH, flow rate, COD and BOD levels.
The common methods of biological treatment for industrial wastewater of this type, are the activated sludge process (aerobic) and the anaerobic digestion process. Anaerobic digestion is known to provide methane as an energy incentive. However, terephthalic and p-toluic acids have been demonstrated to inhibit anaerobic methanogenesis (Guyot et al. , 1990; Macaroon and Guyot, 1992). Moreover, our preliminary experiments to study the feasibility of anaerobic digestion using synthetic wastewater containing about 7 - 10jg of terephthalic acid per liter, along with benzoic acid, acetic acid, methanol and isophthalic acid had shown very low rates off methane generation; the COD reduction rate did not exceed 0.08 kg per m3 of reactor volume per day. For efficient anaerobic digesters, the COD reduction rate is usually of the order of 4 - 20 kg/m3.day; low COD reduction rate in our

experiments may be attributed to the high concentration of inhibitory substances in the waste stream. If terephthalic acid containing streams show a tendency to inhibit anaerobic methanogenesis, it then becomes man datary to develop an efficient process using aerobic microorganisms so as to degrade the pollutant loads of the production facilities of PTA. It is an objective of this invention to develop such a process using aerobic microorganisms.
Aerobic biological treatment schemes generally involve the activated sludge processes. In these processes, several different bacteria and fungi grow together as biomass, and the biomass is usually separated and a portion of it is returned to the biological reactor. Essentially, this requires equipments for biomass sludge separation and sludge recycle. At the microbial level, carbon compounds that contribute COD are broken down into simpler molecules and most of it utilized for the growth of biomass; a portion of the carbon compounds are finally converted to carbon dioxide. The requirement of nutrients (nitrogen and phosphorus) is generally high for activated sludge processes. Unlike activated sludge processes, the nutrient requirements of mixed culture processes seem to be fairly low. Moreover, mixed culture processes do not generate bulk sludge (Gurus Amy, 1988) and hence sludge handling systems can be dispensed with. In view of these factors, one of the objectives of the present invention is to develop a mixed culture microbial process using selected bacterial species for the treatment of petrochemical wastewater containing terephthalic acid and such other sparingly soluble

compounds along with acetic acid, so as to reduce the nutrient costs and sludge handling costs.
Mixed culture system for the treatment of urea wastewater was probably the first to be developed (Indian patent 163,938) by 1985, followed by mixed culture processes for glycol wastewater
(Indian patent application 745/MAS/89), for coke-oven plant effluents containing phenol, thiocyanates, cyanides, tar, oil, grease, sulphides, benzene and catechols (Indian patent application 77/MAS/94), for fish processing plant effluents
(Indian patent application 78/MAS/94) , and for epichlorohydrin plant effluents that contain glycerol, polyglycerol, isopropyl chloride, trichloropropane, propylene and epichlorohydrin (Indian patent application 76/MAS/94); on these lines, the objective of the present invention is to develop a mixed culture microbial process capable of operating under non-sterile conditions for the degradation of sparingly soluble aromatic acids, including terephthalic acid, along with any aliphatic compounds.
DESCRIPTION OF THE INVENTION
The wastewater that is to be treated to reduce the COD and BOD levels, contains aromatic acids that are sparingly soluble; the target substances include, terephthalic acid, p-toluic acid, benzoic acid, isophthalic acid, etc., and aliphatic such as acetic acid. The total chemical oxygen demand contributed by these chemicals in effluents from PTA production is in the range of 3000 - 20,000 mg/1. The solubility of each of these compounds at ambient temperature is fairly low as indicated below, and if

solubilized by the addition of an alkali, the contribution to chemical oxygen demand will be high as indicated by the theoretical COD for each item:
Theoretical COD Solubility in water (mg/g) (g/1 of water)
terephthalic acid 1,446 trace
p-toluic acid 2,117 trace
benzoic acid 1,967 5
isophthalic acid 1,446 0.125
However, due to the presence of solvents, like acetic acid, dioxins, ethylene glycol and acetaldehyde in the effluent, more of the sparingly soluble substances tend to solubilize in water. Moreover, due to the usage of sodium hydroxide for washing < purposes in PTA plants, many of the sparingly soluble acids are neutralized, and the corresponding sodium salts dissolve well in water increasing the COD load. As it is understood that many of these aromatic acids are sparingly soluble, the first step in the treatment of wastewater is precipitation by adjusting the pH. By reducing the pH to 2 - 5, preferably to the range of 2.5 - 3.5, most of the sparingly soluble substances are precipitated, which may be separated by a suitable separation device such as, clarifier, thickener, filter, or centrifuge, and the dewatered sludge can be incinerated or reused. As shown by the examples below, the reduction in COD of the wastewater by way of precipitation is normally in the range of 40 - 60%.

Not all of the acids are totally precipitated out of the solution; acetic acid is soluble in water in all proportions, and due to the presence of acetic acid, certain concentrations of COD contributing substances are likely to be available in solubilized form in water. The wastewater, whose COD is reduced by precipitation, can be treated in a biological reactor with a consortium of specially developed, natural, strains to reduce the COD to acceptable levels. The mixed culture of bacterial strains are found to versatile, require minimal nutrients, and do not generate significant quantities of bio-sludge. Two mixed cultures are developed that work independently to reduce the concentration of dissolved organics in water. In one of the mixed cultures (identified as culture Cl in the following examples), a Pseudomonas sp. was predominantly present in a consortium of other bacterial species; in the second mixed culture (identified as culture C2 in the following examples) presence of a Flavobacterium sp. was confirmed. These bacterial strains were identified according to the Berge’s Manual of Systematic Bacteriology. The cultures were able to degrade the target compounds under non-sterile conditions indicating that the constituent microbes were dominant under such environmental conditions. Temperatures were not controlled in any of the experiments and the performance of the mixed cultures were found to be consistent at all ambient temperatures (usually in the range of 15 - 40°C in our locality) in continuous flow systems over a period of several months.
The pattern of degradation by mixed cultures were found to remain

unaffected by the presence of inorganic ions such as cobalt and manganese, each to a maximum concentration of 10 ppm. Further, the mixed cultures were found to degrade related compounds such as, phenol, p-xylene, o-toluic acid and benzaldehyde. The mixed cultures were able to sustain themselves, as well as able to mineralize the incoming pollutants. Hence, inoculation was required only once; separation of microbial sludge, and its recycling to the bioreactor to serve as the inoculums for bacteria were not required. Moreover, the nutrient requirements for activated sludge processes are typically given as, COD: N: P :: 100: 8: 1. For the mixed culture process developed in this invention, nutrient supply as low as COD: N: P :: 100: 3: 0.25 was found to be adequate. Nutrient consumption is a major operating cost that is encountered throughout the life of a biological process; nutrient requirement is reduced by more than half when compared to activated sludge processes and it is a significant cost saving measure in this invention.
Reduction of COD and BOD occur simultaneously and the general trend of COD reduction in the bioreactor is shown in Figure 1. It is contemplated that any requisite equipment will either be commercially available or readily fabricated by those skilled in the art, and hence, detailed description of such equipment is believed to be unnecessary. The following specific examples illustrate the practice of the process:
EXAMPLE 1
A synthetic wastewater was prepared by dissolving the following

components in water using 10% sodium hydroxide: acetic acid 870 mg/1, p-toluic acid 790 mg/1, benzoic acid 524 mg/1, terephthalic acid 1550 mg/1, isophthalic acid 23 mg/1, and methanol 120 mg/1. The chemical oxygen demand of the synthetic wastewater was found to be 6000 mg/1 approximately. Yeast extract and dominium phosphate were used as nutrients that provide nitrogen to the bacteria; 85 mg of nitrogen per liter of wastewater was added, of which roughly 5 0% was inorganic nitrogen. On the addition of mixed culture Cl, the COD of the wastewater was found to decrease. This experiment was performed in a shake flask. The rate of reduction of COD followed the general trend (marked as Example 1) as shown in Figure I. The experiment was repeated several times by using the same mixed culture and the pattern of COD reduction was similar to that shown in Figure I. More than 90% of the initial COD was degraded.
EXAMPLE 2
The following substances were dissolved in one liter of water using caustic lye to prepare synthetic effluent: acetic acid 883 mg, p-toluic acid 915 mg, benzoic acid 606 mg, terephthalic acid 1596 mg, and isophthalic acid 34 mg. The COD of this synthetic effluent was 6160 mg/1. The pH of the effluent was 11, which was then reduced to 2.6 using 5N sulphuric acid. Several of the dissolved components were found to precipitate on reduction of the pH. The precipitate was filtered and separated, and the COD of the .clear filtrate was found to be 2590 mg/1, which implies that nearly 55% of the inlet COD had been precipitated out. The pH of the clear filtrate was increased to 6.5 using 5N NaOH and

then the clear wastewater was inoculated with mixed culture Cl; sodium nitrate, potassium monohydrate phosphate and potassium dehydrogenize phosphate were used as nutrients for the bacteria; 16.5 mg of N per litre and 4 0.6 mg of P per litre were added. On biodegradation in a shake flask, the COD of the wastewater was found to be reduced to 300 mg/1 in 96 hours. The general trend of COD reduction (marked as Example 2) is shown in Figure I.
EXAMPLE 3
Synthetic effluent was prepared by dissolving the following components in water using caustic lye: 0.8 g/1 of benzoic acid, 1.85 g/1 of terephthalic acid, 1.28 g/1 of acetic acid, 1.23 g/1 of p-toluic acid, 30 mg/1 of isophthalic acid, 17 mg/1 of dioxin, 13 mg/1 of ethylene glycol, and 10 ppm each of cobalt acetate and manganese chloride. The pH of the synthetic effluent was 12 and its chemical oxygen demand was 8200 mg/1. By the addition of HC1 (12% acid), the pH of the synthetic effluent was reduced to 3.5 and several of the dissolved organics were found to precipitate. The precipitate was filtered off and separated. The COD of the clear wastewater was 4000 mg/1, which indicated that nearly 50% of the dissolved COD was removed by precipitation. The clear effluent was treated with mixed culture Cl in a series of three bioreactors, with working volumes of 12.4, 13.2 and 11.0 litres respectively. For the treatment of wastewater, these bioreactors provided residence times of 19.6, 21.0 and 17.5 hours respectively, so that the total residence time was 58.1 hours. Mixed culture Cl was used, with urea, dominium phosphate, and ferrous ammonium sulphate as nutrients providing a total of 36.6

mg of N per litre. The general trend of COD reduction is marked as 'Example 3' and shown in Figure I. The COD and BOD of the treated effluent at the exit of the last bioreactor were 220 mg/1 and 60 mg/1 respectively.
EXAMPLE 4
900 mg/1 of acetic acid, 900 mg/1 of p-toluic acid, 600 mg/1 of benzoic acid, 1600 mg/1 of terephthalic acid and 30 mg/1 of isophthalic acid were dissolved in water using caustic lye to prepare a synthetic effluent. The initial pH and COD of the synthetic effluent were 12 and 6000 mg/1 respectively. The effluent was acidified with HC1 and the pH was reduced to 3.0 at which several dissolved components were found to precipitate. The precipitate was removed by filtration and the COD of the clear liquid was found to be 2400 mg/1. The reduction in COD of the effluent due to lowering of pH was nearly 60%. The pH was then corrected to 7.0 and it was inoculated with the mixed culture C2 and kept in a continuously-stirred batch reactor. Ammonium sulphate, dipotassium hydrogen phosphate and yeast extract were used as nutrients, in such a way that 42 mg of inorganic nitrogen per litre, 0.8 mg of amino-nitrogen per litre and 1.8 mg of phosphorus per litre were added. The COD of the effluent was found to decrease with time and the trend is shown in Figure II. The chemical oxygen demand was reduced to 100 mg/1 in 65 hours.
EXAMPLE 5
1.1 g/1 of acetic acid,. 2.1 g/1 of p-toluic acid, 1.6 g/1 of benzoic acid, 0.23 g/1 of isophthalic acid and 9.0 q/1 of

terephthalic acid were dissolved in water using caustic lye to prepare a synthetic effluent. The chemical oxygen demand of this synthetic wastewater was 20900 mg/1. The pH of the wastewater was adjusted to 8.4 and it was inoculated with mixed culture C2. Urea, yeast extract and dominium phosphate were added as nutrients, in such a way that a total of 110.5 mg of nitrogen per litre was provided to the bacteria. The experiment was performed in a continuously-stirred batch reactor and the COD of the wastewater was found to decrease in course of time. Once in every 24 hours, the pH of the culture was adjusted 7.0. The general trend of COD reduction is (marked as Example 5) shown in Figure III. More than 90% of the initial COD was observed to be reduced.
EXAMPLE 6
Synthetic effluent was prepared in the same way as described in Example 4. The pH was reduced to 4 .0 using hydrochloric acid and some the sparingly soluble substances were precipitated out as described in earlier examples. The precipitate was separated and the COD of the clear effluent was found to be 3360 mg/1. Thus, approximately 55% of the dissolved COD had been removed by precipitation. The clear liquid was subjected to biodegradation using mixed culture C2 in a series of three bioreactors with working volumes of 14, 14 and 7 litres respectively. The contents of the bioreactors were well-stirred by a mechanical agitator; nutrient supply was identical to Example 4. The total residence time of the effluent in the bioreactors was 53 hours; at the exit of the third bioreactor, the COD was measured to be 200 mg/1. Synthetic effluent was continuously pumped through the