Anaerobic treatment of sugarcane molasses-based distillery spentwash has been investigated employing diphasic fixed-film reactor technology using granular activated carbon (GAG) as support media for microbial attachment and growth in the second phase. In the first phase, neutralized spentwash was treated with acidogens to produce volatile fatty acids (VFA), which are easily utilizable by methanogens to yield methanogens to yield methane gas. An HRT of 4 days, corresponding to an OLR of 21.3 kg COD m(-3) day(-1) with a COD reduction of 67.1% and gas yield of 0.45 m(3) kg(-1) COD removed with 70% methane content, was achieved in the methane phase. About 50% reduction in media porosity was observed due to accumulation of biomass and inorganics. No apparent inhibition of the methanogenic activity was observed even with a propionic acid concentration of 59.1% (2134 mg l(-1)) of total volatile acids (TVA). Copyright (C) 1996 Elsevier Science Ltd.