Production of hydrogen and methane from alcohol wastewater using two-stage upflow anaerobic sludge blanket reactors

Abstract

In this study, production of H₂ and CH₄ from alcohol wastewater was investigated using two-stage upflow anaerobic sludge blanket reactors (UASB). For the H₂ production step, the first 4-L UASB was operated at different COD loading rates, pH 5.5 and a recycle ratio of feed-to-effluent from methane-producing stage of 1:1. For the CH₄ production step, a second 24-L UASB unit was fed by the effluent from the first UASB. Both UASBs were operated in mesophilic condition (37ºC). To maximize the CH₄ production, the system was operated at a COD loading rate of 48 kg/m³d (based on the first UASB) to provide the gas production rate of 28.53 l/d and 39.56 l/d, respectively. The produced gas contained 64.40% CH₄ and 35.60 %CO₂ and 84.81% CH₄ and 15.19% CO₂ for the first and second UASB, respectively. To maximize the H₂ production, the system was operated at a COD loading rate of 270 kg/ m³d to yield a gas production rate of 9.01 l/d and 16.69 l/d for the first, second UASB, respectively. The produced gas from the first UASB contained 22.15% H₂, 70.48% CO₂ and 7.37% CH₄ while that from the second UASB contained 0% H₂, 49.06% CO₂ and 50.94% CH₄.