The effect of concentration of phenols on their batch methanogenesis

The biodegradability of phenol and six other phenolic compounds (o‐, m‐, and p‐cresol, 2‐, 3‐, and 4‐ethylphenol) was examined in batch methanogenic cultures. The effect of concentration of these alkyl phenols on the anaerobic biodegradation of phenol was also evaluated. The inoculum used in this study was cultivated in a continuous flow laboratory fermenter with phenol as the primary substrate. Phenol, at initial concentrations as high to 1400 mg/L was completely degraded to methane and carbondioxide after 350 hours incubation. Complete degradation of m‐ and p‐cresol was also observed while the ethylphenols and o‐cresol were not significantly degraded. At initial concentrations exceeding 600 mg/L, phenol inhibited the phenol‐degrading microorganisms but not the methanogens. At about 600 mg/L, cresols reduced the rate of phenol degradation to 50% of that observed in a control culture containing only 200 mg/L phenol. Ethylphenols were more inhibitory than cresols. Phenol degrading microorganisms were more susceptible to inhibition by cresols and ethylphenols than were the methanogens. The inhibitory effects of the three isomers of cresol and ethylphenol did not vary with the isomer but rather with the substituted functional group.