Enhanced anaerobic degradation of benzene by enrichment of mixed microbial culture and optimization of the culture medium.

A heterogeneous mixed culture, originally collected from two different sources, namely cow-drug and sludge from the city waste-water treatment plant, was grown in mineral medium containing 1% glucose and then adapted on benzene as the carbon and energy source. Under anaerobic conditions benzene was degraded via benzoic acid as a major intermediate in the benzene degradation pathway. The degradation rate of benzene was improved stepwise by the number of enrichments and optimization of the culture medium. The effects of microaerobic conditions and/or physicochemical treatment with H2O2 prior to anaerobic degradation were studied with respect to variations in benzene degradation rate, growth of biomass and gas composition. It was noticed that the amount of gas produced is less than the theoretical value expected and the percentage of methane in the product gas was very small (3%-3.5%). The reason for this is not well understood but it is presumed that the major group of benzene-degrading bacteria present in the culture medium are sulphate reducers and the mixed consortium is unable to degrade certain complex aromatic intermediates in the benzene degradation pathway under the experimental conditions. For an actual explanation of the situation arising in this study, further investigations must be carried out. However, the mixed culture is capable of oxidizing benzene more rapidly to intermediate compounds and also partly into gas under the culture conditions, compared to the published data for the anaerobic degradation of benzene.