Biodegradation of trace levels of a complex organic pollutant mixture

Three bacterial isolates with the ability to grow on a model mixture of ground water contaminants were obtained from a sewage works for treatment of industrial effluents, and from heavily and intermediately contaminated ground. The mixture consisted of benzene, toluene, o-xylene, nitrobenzene, 1,4-dichlorobenzene, o-cresol, naphthalene, tetrachloromethane and trichloroethylene, at concentrations ranging from 150 to 600 micrograms/l (2.1 mg/l in total). A supplement of 50 mg/l phenol was added to support growth and batch cultures were adapted for 6 weeks. Preliminary assays to check for degradative ability and toxicological assessments of the compounds using oxygen uptake rates were undertaken. Each isolate exhibited a different extent of degradation for the compounds. In 18 h incubation, from an initial figure of 1,966 micrograms/l (not including the primary substrate) the highest remaining total organic carbon of 800 micrograms/l was for the isolate from activated sludge. The effect of the organic compounds upon oxygen uptake rate was less marked for the micro-organisms from heavily polluted ground. As far as bioremediation of groundwater is concerned, the combination of both chemical structure variety and extremely low concentrations of individual chemicals in the mixture under investigation, make the present report relevant to many environmental problems.