METHANOGENIC DEGRADATION OF P-CRESOL IN BATCH AND IN CONTINUOUS UASB REACTORS

Two methanogenic cultures were grown in the presence of p-cresol as so le carbon source or together with a mixture of volatile fatty acids (V FA). Both batch cultures produced methane from VFA in-the presence of p-cresol, up to concentrations of about 200 ppm, in a first experiment , without significant activity inhibition. After several transfers, on e of the cultures tolerated higher p-cresol concentrations. Only that culture, originating from industrial effluents contaminated with pheno lic compounds, was able to remove p-cresol which was completely degrad ed to methane and carbon dioxide with p-hydroxybenzoate, propionate an d acetate as detectable intermediate compounds. These intermediates di d not accumulate in the medium. The addition of VFA as auxilliary carb on sources very slightly delayed p-cresol removal in batch assays but allowed, on the contrary, the use of higher p-cresol influent concentr ations in continuous UASB reactors than in the absence of VFA. With a mixture of p-cresol:VFA al a COD ratio of 2:1, complete COD degradatio n was reached when operating at an hydraulic retention time (HRT) of 0 .67 day and at an influent concentration of 650 ppm p-cresol. When ope rating under the same conditions in the absence of VFA, around 80% p-c resol was removed although a near complete degradation was reached at influent p-cresol concentrations of 400 ppm working at a HRT of 0.8 da y. (C) 1997 Elsevier Science Ltd.