This study evaluated the process performance of a novel treatment system consisting of an acidification reactor, an upflow staged sludge bed (USSB) reactor, an upflow anaerobic sludge blanket reactor, and an aerobic trickling filter for the treatment of a high-strength molasses wastewater with a chemical oxygen demand (COD) of up to 120,000 mg/L. The USSB operating at 35 degrees C was capable of achieving an organic loading rate of 11 kgCOD/m(3) day with a methane recovery of 62.4% at an influent COD of 120,000 mg/L. The final effluent COD was 4520 mg/L. The system was effective with regard to nitrification and sulfur removal. Fifty percent inhibition of the bacterial activity of the retained sludge by the cations was determined at 8 gK/L for sucrose degradation, 16 gK/L for sulfate reduction, and 12 gK/L or 9 gNa/L for acetoclastic methane production. Cation inhibition of anaerobic degradation reduced the process performance of the USSB. (C) 2012 Elsevier Ltd. All rights reserved.