Removal of phenolic compounds from a petrochemical effluent with a methanogenic consortium

A methanogenic consortium was used to degrade phenol and ortho- (o-) cresol from a specific effluent of a petrochemical refinery. This effluent did not meet the local environmental regulations for phenolic compounds (178 mg/L), oils and greases (61 mg/L), ammoniacal nitrogen (75 mg/L) or sulfides (3.2 mg/L). The consortium, which degrades phenol via its carboxylation to benzoic acid, was progressively adapted to the effluent. Despite the very high effluent toxicity (EC50 of 2% with Microtox), the adapted consortium degraded 97% of 156 mg/L phenol in the supplemented effluent after 13 days in batch cultures (serum bottle). The addition of proteose peptone to the effluent is essential for phenol degradation. o-cresol was also transformed but not meta- or para-cresols. A continuous flow fixed-film anaerobic bioreactor was developed with the consortium. Treating the effluent with the bioreactor reduced phenol and phenolic compounds concentrations by 97 and 83%, respectively, for a hydraulic residence time of 6 h. This treatment also reduced by about half the effluent toxicity. Oils and greases and ammoniacal nitrogen were not affected. Similar microbiological forms were observed in serum bottles and in the bioreactors with or without the petrochemical effluent. These results indicate that this methanogenic consortium can treat efficiently the phenolic compounds in this specific petrochemical effluent.