Hydrogen production by organic wastewater fermentation in anaerobic baffled reactor

Hydrogen production from diluted molasses by anaerobic activated sludge was investigated in an anaerobic baffled reactor (ABR) under continuous flow condition. The reactor was made of organic glasses and had three chambers, and the effective volume of each chamber was 9.16 L. The inoculated sludge was the excess sludge taken from a second settling tank in a local wastewater treatment process. The reactor started up at the organic loading rate (OLR) of 8.89 kg COD·(m³·d)^-1 with a hydraulic retention time (HRT) of 13.5 h and a temperature of (35±l)°C. After 25 days operation without pH control, the reactor attained a stable state for hydrogen evolution with an average yield of hydrogen of 32.0 L·d^-1, namely an average biogas yield of 59.0 L·d^-1 during the next 30 days of operation. During the stable operation process, the ranges of effluent pH, oxidation-reduction potential (ORP) and alkalinity in term of CaCO₃ were 4.2 to 4.4, -230 mV to -250 mV and 240 mg·L^-1 to 350 mg·L^-1, respectively. Different hydrogen yields were observed by 10% to 20% among the three chambers. The biomass in the reactor maintained at 30.39 g·L^-1 in term of volatile suspended solid (VSS) and specific hydrogen production rate reached at 76.64 L·(kg VSS·d)^-1. Along with the production of hydrogen by organic wastewater fermentation, organic acids were produced as by-products, among which ethanol and acetic acid were dominant. This indicated that ethanol type fermentation performed in the reactor. Contrasting with other kinds of reactors used to produce hydrogen, the fermentative hydrogen-producing baffled reactor is anticipated to be a wildly applied in the filed due to its simple design, stable process, flexible operation and high volumetric utilization rate, etc.