Anaerobic Biodegradation of Nitrogen-Substituted and Sulfonated Benzene Aquifer Contaminants

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Abstract
A literature survey of ground water contaminants indicated that aquifers are repositories for hazardous wastes, including N- and S-substituted benzene derivatives. We therefore examined the susceptibility of several anilines, benzamides, benenesulfonic acids and benenesulfonamides to anaerobic metabolism by aquifer microorganisms. Under sulfate-reducing and methanogenic conditions the carboxylated anilines were biotransformed within 1 to 3 months while unsubstituted or methylated anilines required longer incubation times. Benzamide as well as an aryl methyl and an N-methyl derivative were biodegraded under both redox conditions. The anaerobic degradation of the N-methylated benzamide was favored in sulfate-reducing rather than methanogenic incubations. However, the addition of a second N-alkyl group rendered the resulting compounds resistant to anaerobic decay. Only 1 of 7 benzenesulfonates and 2 of 5 benzenesulfonamides proved amenable to anaerobic metabolism. We found 37-75% of the theoretically expected amount of methane from aquifer slurries amended with the aminobenzoic acids, benzamide, and p-toluamide. In the sulfate-reducing aquifer slurries 89-100% of the oxidized benzamide, p-toluamide and N-methylbenzamide could be accounted for by sulfate reduction. These results help indicate which hazardous waste constituents will likely persist in anoxic aquifers and the types of chemical substitution patterns that favor anaerobic biotransformation.