Improvement of hydrogen production with added fermentation residue and using two-stage anaerobic process under thermophilic temperature

Abstract

The two main objectives of this study were to maximize hydrogen production from alcohol wastewater with added fermentation residue and to optimize the separate production of hydrogen and methane from cassava wastewater using high rate anaerobic processes under thermophilic temperature. For the first part, hydrogen production from alcohol wastewater was investigated using anaerobic sequencing batch reactor (ASBR) operated at 55 ℃ and pH 5.5. Under an optimum COD loading rate of 68 kg/m3d, the ASBR provided the highest hydrogen production performance in terms of the highest H2 content of 43 %, the highest hydrogen yield of 30 L/kg COD applied (or 130 1/kg COD removal) and the highest specific hydrogen production rate of (SHPR) of 2.1 L/L d (or 560 L/kg MLSS d). For the second part, the ASBR unit was operated at the optimum COD loading rate of 68 kg/m3d of the alcohol wastewater at different concentrations of added fermentation residue under pH 5.5 and 55 ℃. At an optimum concentration of added fermentation residue of 1,000 mg/L (as dried weight), the hydrogen production performance increased about 10 % as compared to the system without added fermentation residue. Under the optimum conditions, only cellulose (41.6 %) and hemicellulose (21.8 %) were broken down while lignin was not digested. For the third part, both production of hydrogen and methane from cassava wastewater was investigated using a two- stage up flow anaerobic sludge blanket (UASB) system operated at 55 ℃ for both UASB units while only the pH in the hydrogen UASB unit was maintained at 5.5. The recycle ratio of the effluent from the methane bioreactor-to-the feed Bow rate was fixed at 1:1. When the system was operated under an optimum COD loading rate of 90 kg/m3d based on the feed COD and the hydrogen UASB volume or 15 kg/m3d based on the feed COD and the methane UASB volume, the hydrogen UASB unit provided the a highest hydrogen yield and specific hydrogen production rate of 90.5 L H2/kg COD removed and 520 L H2/m3d, respectively. At the same optimum COD loading rate, the methane UASB unit provided a maximum methane yield and specific methane production rate of 540 L CH4/kg COD removed and 650 L /m3d, respectively. For all studied bioreactors, both nitrogen and phosphate uptakes were maximal at the optimum conditions for hydrogen and methane production and no significantly different in both hydrogen and methane production units. Most nitrogen uptake was derived from organic nitrogen. The toxic levels of total volatile organic acids (VFA) to hydrogen-producing bacteria and methane-producing bacteria were 10,000 and 400 mg/L as acetic acid, respectively.