Anaerobic Treatment of Phenolic Wastewaters

Phenolic pollutants are commonly found in wastewaters from synthetic chemicals, pesticides, coal conversion, pulp-paper, oil-refining, plastics, and pharmaceuticals industries. They are of significant environmental concerns because of their toxicity and potential carcinogenic property. The upflowanaerobic sludge blanket (UASB) process has been found effective for the degradation of many recalcitrant pollutants, including phenols. However, phenolic pollutants at high concentrations in wastewater may also inhibit the bioactivities of the granular sludge and consequently lower the treatment efficiency. This paper is to review literature on the anaerobic treatment of phenolic pollutants with emphasis on the following aspects: (1) phenolic inhibitory effect to the anaerobes, and the tolerance levels; (2) treatment of phenolic wastewater in anaerobic reactor of various designs; (3) effects of operating factors, including hydraulic retention time, effluent recirculation, temperature, loading shock and co-substrate on the biodegradation of phenols; and (4) the anaerobes and the degradation pathway involved in anaerobic degradation of phenols. Overall, phenolic pollutants in wastewater, when operated below the inhibitory concentrations and avoiding the loading shocks, can be effectively degraded under anaerobic processes with proper sludge acclimation, effluent recirculation and, if necessary, co-substrates.