Enhancement of aerobic degradation of benzoate and 2-chlorobenzoate by adapted activated sludge

Activated sludge from the Stickney Water Reclamation Plant of the Metropolitan Water Reclamation District of Greater Chicago was adapted in the laboratory to either benzoate or 2-chlorobenzoate as the sole carbon source in sequencing batch reactors with a 48-h feed-aerate-settle-draw cycle and a mean cell residence time (MCRT) of 10 days. Benzoate degradation increased by more than 80-fold after 7 MCRTs compared to unadapted activated sludge. A greater than 15-fold increase in 2-chlorobenzoate metabolism occurred after adaptation for about 5-7 MCRTs. For each substrate the maximum rate measured for adapted cultures was near or above the highest previously reported in the literature. For both adapted and unadapted sludges, benzoate metabolism was considerably faster than that of 2-chlorobenzoate, and for both substrates the rate of metabolism increased incrementally with time of adaptation. As expected, addition of the benzoate-adapted sludge to unadapted sludge enhanced the latter's ability to degrade benzoate. (C) 2009 Elsevier GmbH. All rights reserved.