TOXICITY OF N-SUBSTITUTED AROMATICS TO ACETOCLASTIC METHANOGENIC ACTIVITY IN GRANULAR SLUDGE

N-substituted aromatics are important priority pollutants entering the environment primarily through anthropogenic activities associated wit h the industrial production of dyes, explosives, pesticides, and pharm aceuticals, Anaerobic treatment of wastewaters discharged by these ind ustries could potentially be problematical as a result of the high tox icity of N-substituted aromatics. The objective of this study was to e xamine the structure-toxicity relationships of N-substituted aromatic compounds to acetoclastic methanogenic bacteria, The toxicity was assa yed in serum flasks by measuring methane production in granular sludge , Unacclimated cultures were used to minimize the biotransformation of the toxic organic chemicals during the test. The nature and the degre e of the aromatic substitution were observed to have a profound effect on the toxicity of the test compound. Nitroaromatic compounds were, o n the average, over 500-fold more toxic than their corresponding aroma tic amines. Considering the facile reduction of nitro groups by anaero bic microorganisms, a dramatic detoxification of nitroaromatics toward s methanogens can be expected to occur during anaerobic wastewater tre atment. While the toxicity exerted by the N-substituted aromatic compo unds was closely correlated with compound apolarity (log P), it was ob served that at any given log P, N-substituted phenols had a toxicity t hat was 2 orders of magnitude higher than that of chlorophenols and al kylphenols. This indicates that toxicity due to the chemical reactivit y of nitroaromatics is much more important than partitioning effects i n bacterial membranes.