Methanogenic Degradation of Phenol and Benzoate in Acclimated Sludges

Abstract

Anaerobic phenol and benzoate degrading consortia were cultivated by acclimation of methanogenic sludges to be capable of degrading completely to CO2 and CH4 1,000 mg/l of phenol within 5–7 days, and 3,000 mg/l of benzoate within 5–7 days, respectively. By using the acclimated sludges, the effect of gaseous atmospheres (H2:CO2/80:20 and N2:CO2/80:20) on the biodegradability and the degradation pathways of phenol and benzoate were examined. Although the anaerobic degradation of phenol was accelerated in the H2/CO2 atmosphere compared with the N2/CO2 atmosphere, benzoate was accumulated. Degradations of benzoate and butyrate were inhibited in the H2/CO2 atmosphere under stirred conditions, but not under static conditions. Through a series of biodegradation tests by using several intermediates in phenol degradation reported previously, the anaerobic degradation pathway of phenol in the N2/CO2 atmosphere was suggested to be phenol → benzoate → cyclohexane carboxylate (or 1-cyclohexene carboxylate) → fatty acids → CO2,CH4.