Hydrogen and methane production from biodiesel wastewater by two-stage anaerobic sequencing batch reactor (ASBR) under mesophilic temperature

Abstract

Simultaneous production of hydrogen and methane from biodiesel wastewater with added glycerine was investigated by using a two-stage anaerobic sequencing batch reactor (ASBR) system. A hydrogen reactor (4 L) and methane reactor (24 L) were operated under mesophilic temperature (37 ºC) at 6 cycles/d. The pH in the hydrogen bioreactor was controlled at 5.5 while the pH in the methane bioreactor was not controlled. Glycerine was added to the biodiesel wastewater at 3.5 % w/v to obtain a constant feed chemical oxygen demand (COD) of 45000 mg/l. A recycle ratio of 1:1 was used to minimize the NaOH addition in the hydrogen reactor used for pH adjustment. The two-stage ASBR system was operated at different COD loading rates (33.75-84.38 kg/m³d based on the hydrogen ASBR system or 5.63-14.06 kg/m³d based on the methane ASBR system). The highest hydrogen production performance, in terms of hydrogen yield (7.8 ml H₂/g COD removed) and specific hydrogen production rate, SHPR (88.9 ml H₂/g MLVSS d), was found at a COD loading rate of 67.50 kg/m³d. The highest methane production performance, in terms of methane yield (128.4 ml CH₄/g COD removed) and specific methane production rate, SMPR (232.5 ml CH₄/g MLVSS d), was found at a COD loading rate of 11.25 kg/m³d.