Fungal treatment of an edible-oil-containing industrial effluent

A typical edible oil-processing plant discharges large volumes of effluent high in Chemical oxygen demand (COD). This leads to fines from the municipality and the consequent loss of profit. In this study the effluent composition of an oil-processing plant was monitored for 1 year. The COD ranged between 16,000 and 250,000 mg/l and the conductivity between 88.2 and 268 mS/m. It is known that edible oil is a good carbon source and Mucoralean fungi have the ability to accumulate large quantities of oil. Therefore, the reduction of the COD by 12 fungal strains (from culture collections) was determined. The most promising organisms were Rhizopus stolonifer (CBS 263.28), reducing the COD by 91.3%, a Penicillium species (TUTC 077) by 85.3%, Mucor circinelloides f. circinelloides (CBS 108.16) by 84.0% and Aspergillus niger (TUTC 120) by 83.8%. Although the reduction of the effluent COD was significant, the lowest COD of 1625.08 mg/l was still higher than the legal limits. This led to the isolation of fungi from soil, using selective media. Fifty-eight fungal strains were isolated, of which seven isolates could reduce the COD to below 760 mg/l (legal limit). The best isolate reduced the COD by 98.2% from 16,000 to 286.96 mg/l and was identified as Cunninghamella echinulata. The best COD reducers were tested for their ability to produce gammalinolenic acid (GLA) as a high value by-product. All these isolates were able to produce GLA and the best production was obtained from Emerisella nidulans, namely 408.70 mg GLA/l.