Inhibition of acetate methanogenesis by phenols

The concentration effects of phenol and nine monosubstituted phenols (catechol, resorcinol, hydroquinone, 2-chlorophenol, 3-chlorophenol, 4-chloro- phenol, 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol) on the methanogenic fermentation of acetate were evaluated with batch anaerobic toxicity assays. The rate of methane production decreased progressively with increasing concentration of phenolic compounds. The inhibitory effect of the substituted phenols toward the acetate-utilizing methanogens was more correlated to substituent type rather than substituent position. The inhibition was in the order of nitrophenols > chloro- phenols > hydroxy phenols. Hydroxyphenols were less inhibitory than the unsubstituted phenol. Experimental data were analyzed using three common inhibition models (competitive, noncompetitive, and uncompetitive) by the Marquardt method of nonlinear regression and Statistical Analysis Systems (SAS) computer programs. The noncompetitive inhibition model was found to best fit the experimental data with inhibition constant, K_I determined at about 1-5 mg/L for nitrophenols, 100400 mg/L for chlorophenols, 1,000-2,000 mg/L for hydroxyphenols, and 900 mg/L for phenol.