Anaerobic digestion of dairy cow manure (CM), the organic fraction of municipal solid waste (OFMSW), and cotton gin waste (CGW) was investigated with a two-phase pilot-scale anaerobic digestion (AD) system. The OFMSW and CM were digested as single wastes and as combined wastes. The single waste digestion of CM resulted in 62 m(3) methane/ton of CM on dry weight basis. The single waste digestion of OFMSW produced 37 m(3) methane/ton of dry waste. Co-digestion of OFMSW and CM resulted in 172 m(3) methane/ton of dry waste. Co-digestion of CGW and CM produced 87 m(3) methane/ton of dry waste. Comparing the single waste digestions with co-digestion of combined wastes, it was shown that co-digestion resulted in higher methane gas yields. In addition, co-digestion of OFMSW and CM promotes synergistic effects resulting in higher mass conversion and lower weight and volume of digested residual. (c) 2008 Elsevier Ltd. All rights reserved.