Influence of monochlorophenols on methanogenic activity in granular sludge

The effects of monochlorophenols (MCPs) on volatile fatty acid degradation by methanogenic granular sludge from two full scale upflow anaerobic sludge blanket (UASB) reactors treating potato processing wastewater, were tested. Sludges 1 and 2 were derived from the first reactor, and sludge 3 from the second reactor. Methane production and utilization of acetate, propionate and butyrate were measured. Methane production by sludge 3 was more severely inhibited by MCPs (50% inhibition around 0.6 mM or less) than were sludges 1 and 2 (50% inhibition above 1 mM). Aceticlastic methanogens, propionate degrading consortia and butyrate degrading consortia of the two sludges had a different sensitivity. In sludge 3, the acetate utilization was most sensitive, while for the other sludges, butyrate utilization was inhibited most strongly. In an experiment with stored sludge, the inhibition was reversible, but depended on the exposure time. In addition, stored sludge was less active and more sensitive to MCPs compared to fresh sludge. An activation period after cold storage lowered the sensitivity of the sludge to 2-CP. These findings may be important when stored sludge is used to start up a reactor to treat wastewater that contains toxic compounds.