Two-step hydrogen and methane production from cassava wastewater using upflow anaerobic sludge blanket reactors

Abstract

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.