Direct integration of CSTR-UASB reactors for two-stage hydrogen and methane production from sugarcane syrup

This study attempted to directly integrate a continuous stirred tank reactor (CSTR) with an up-flow anaerobic sludge blanket (UASB) reactor for two-stage hydrogen and methane production. CSTR was used to produce hydrogen from a 25 g-COD/L sugarcane syrup. The hydrogenogenic effluent from CSTR was directly fed to UASB for methane production. The working volumes of CSTR and UASB reactors were 1 and 24 L, respectively. Optimization of hydraulic retention times (HRT) for two-stage hydrogen and methane production after an integration were examined. A maximum hydrogen production rate of 17.5 L/L.d and methane production rate of 2.25 L/L.d were achieved at optimal HRTs of 3 h in the CSTR and 3 d in the UASB with a total energy production rate of 270 kJ/L.d. The two-stage reactors performed well in producing hydrogen and methane over 200 days with a total COD removal of 97.5%. The natural microflora in sugarcane syrup was greatly affected by HRT but HRT did not affect the archaea community. The volatile fatty acids to alkalinity ratio in the UASB reactor was below the critical value of 0.4 at every HRT, indicating stability of a long term methane production process with direct feeding of non-pretreated hydrogenogenic effluent. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.