The main objective of this study was to produce both hydrogen and methane from cassava wastewater using two sequential steps of upflow anaerobic sludge blanket reactors (UASB). Each UASB had a liquid holding volume of 24 L and was operated at a constant temperature of 37°C. The organic concentration of the studied cassava wastewater, in terms of chemical oxygen demand (COD), was in the range of 19,000 to 22,000 mg/L. For the hydrogen production step, the UASB system was operated at a constant pH of 5.5 by recycling the effluent and at different COD loading rates. A maximum volumetric hydrogen production rate of 0.39 L/Ld and a maximum hydrogen yield of 39.8 L/kg COD removed were found at a COD loading rate of 25 kg/m³d. The Produced gas under the optimum conditions contained 36.4% H₂, 63.6% CO₂, and no methane production. For the methane production step, the studied UASB was fed by the effluent produced from the hydrogen production step at a COD loading rate of 25 kg/m³d. The system was operated at a constant temperature of 37°C without pH control to obtain the maximum methane production.
