This study evaluates a two-stage bioprocess for recovering bioenergy in the forms of hydrogen and methane while treating organic residues of ethanol fermentation from tapioca starch. A maximum hydrogen production rate of 0.77 mmol H(2)/g VSS/h can be achieved at volumetric loading rate (VLR) of 56 kg COD/m(3)/day. Batch results indicate that controlling conditions at S(0)/X(0) = 12 with X(0) = 4000 mg VSS/L and pH 5.5-6 are important for efficient hydrogen production from fermentation residues. Hydrogen-producing bacteria enriched in the hydrogen bioreactor are likely utilizing lactate and acetate for biohydrogen production from ethanol-fermentation residues. Organic residues remained in the effluent of hydrogen bioreactor can be effectively converted to methane with a rate of 0.37 mmol CH(4)/g VSS/h at VLR of 8 kg COD/m(3)/day. Approximately 90% of COD in ethanol-fermentation residues can be removed and among that 2% and 85.1% of COD can be recovered in the forms of hydrogen and methane, respectively. (C) 2010 Elsevier Ltd. All rights reserved.