Two-stage biological treatment of olive mill wastewater with whey as co-substrate

The two-stage system operated satisfactorily up to an organic loading rate (OLR) of 3.0 kg COD L−1 day−1 with a biogas production rate of 1.25 Lbiogas Lreactor−1 day−1 and a total COD reduction in excess of 93% (62% COD reduction in aerobic pretreatment and 83% COD reduction in anaerobic digestion). Fifty-four percent of the phenol was biodegraded during the aerobic treatment stage, and biogas with between 68% and 75% methane was produced during anaerobic digestion.