Batch anaerobic co-digestion studies were conducted using 21 mixtures (M1-M21) of food waste (FW), primary sludge (PS), and waste activated sludge (WAS) at 37 degrees C and an initial pH of 5.5 +/- 0.2. The results showed that co-digestion of FW and sludges had a positive impact on the hydrogen production. The maximum hydrogen yields by co-digestion of FW + PS, FW + WAS, and FW + PS + WAS were achieved at volumetric ratios of 75:25, 75:25, and 80:15:5, respectively, with corresponding optimal COD/N mass ratios of 26, 31 and 30, respectively. Furthermore, the synergistic effect of co-digestion was proven and quantified: the measured hydrogen productions were higher than the sums of the hydrogen productions calculated from each fraction, and the highest percentage increase above the calculated value of 101%, was achieved in the FW + PS + WAS mixture (80:15:5). (C) 2012 Elsevier Ltd. All rights reserved.