Hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactors (UASB) with an emphasis on maximum hydrogen production

•The VFA inhibition level for hydrogen-producing bacteria is 10,000 mg/L.•The VFA inhibition level for methane-producing bacteria is 400 mg/L.•The produced gas of second-stage UASB contained a very high content of CH4 (>80%).

The objective of this study was to produce hydrogen and methane from cassava wastewater using two steps of upflow anaerobic sludge blanket reactors (UASB), emphasizing maximum hydrogen production. For the first hydrogen production stage, the UASB system was operated at 37 °C and pH 5.5 at different COD loading rates. A maximum specific H2 production rate of 0.39 l H2/l d and a maximum H2 yield of 39.83 l H2/kg COD removed were found at a COD loading rate of 25 kg/m3d and the gas produced contained 36.4% H2, and 63.6% CO2 without methane. For the second methane production stage, the UASB was fed by the effluent produced from the hydrogen production step operated at the optimum COD loading rate. A maximum specific CH4 production rate of 0.91 l CH4/l d and a maximum CH4 yield of 115.23 l CH4/kg COD removed were found at a COD loading rate of 8 kg/m3d. The inhibition levels of organic acids to acidogens and methanogens were found to be 10,000 and 400 mg/l as acetic acid, respectively.