Simultaneous removal of phenol, ortho- and para-cresol by mixed anaerobic consortia

Abstract

Two different anerobic consortia, one removing phenol and ortho- (o-) cresol and the other removing para- (p-) cresol, were cultivated in serum bottles using whey as cosubstrate substitute for proteose peptone. Phenol and p-cresol removal with the phenol-removing consortium were the same with 0.0125% (w/v) whey as with 0.05% proteose peptone. For the other consortium, 8 days were required to decrease the p-cresol concentration from 35 to 2 mg/L with 0.025% whey, while 35 days were required to achieve a similar removal with 0.5% proteose peptone. The two consortia were mixed and cultivated with 0.025% whey. Phenolic compound removal with the mixed consortia was as good as that achieved by each of the two initial consortia against their respective substrates. This removal activity was maintained after several transfers. In a continuous upflow fixed-film reactor, the mixed consortia removed over 98% of 150 mg/L of phenol and 35 mg/L of each o- and p-cresol in the influent at 29°C, with 0.025% whey as cosubstrate. The hydraulic retention time (HRT) was 0.25 day, corresponding to a phenolic compound volumic loading rate of 880 mg/(L of reactor × day). Once the continuous flow reactor achieved constant phenolic compound removal, no intermediates were found in the effluent, while in serum bottles, m-toluic acid, an o-cresol intermediate, accumulated. Measurements of the specific activity for the uptake of different substrates demonstrated the presence of all trophic groups involved in methanogenic fermentation. These activities were, in mg of substrate/(g of volatile suspended solids × day), as follows: 849 ± 25 for the acidogens; 554 ± 15 for the acetogens; 934 ± 37 for the aceticlastic methanogens; and 135 ± 15 for the hydrogenophilic methanogens. Electron micrographs of the mixed consortia showed seven different morphological bacterial types, including Methanotrix-like bacteria.Key words: anaerobic degradation, fixed-film reactor, proteose peptone, whey, phenolic compounds.