Synthetic leachate with different initial concentrations of acetate (500-2500 mg HAc/L) and propionate (500-3500 mg HPr/L) was treated with active biomass acclimated to landfill leachate under anaerobic mesophilic conditions for 72 h. Methanogenesis was observed within all samples during the first 48 h. The greatest removal of acetate (80-100%) and propionate (15-35%) was achieved in tests with initial concentrations ranging from 1500 to 1900 mg HAc/L and from 1000 to 1800 mg HPr/L. Concurrent with the removal of acids, pH increased between 0.3 and 0.45 units, to above the threshold pH for precipitation of CaCO3. Therefore, some 50-70% of dissolved Ca2+ was removed from solution. This study suggests that by using an equalization tank (prior to the anaerobic digester) to maintain the acetate and propionate concentrations to within their optimum range would help to alleviate clogging through the removal of dissolved Ca2+ and maximizing CH4 production. (C) 2011 Elsevier Ltd. All rights reserved.