Methanogenic Degradation of Phenol and Benzoate in Acclimated Sludges

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.