Optimization of biohydrogen production of palm oil mill effluent by ozone pretreatment

The biohydrogen (H-2) production in batch experiments under varying concentrations of raw and ozonated palm oil mill effluent (POME) of 5000-30,000 mg COD.L-1, at initial pH 6, under mesophilic (37 degrees C), thermophilic (55 degrees C) and extreme-thermophilic (70 degrees C) conditions. Effects of ozone pretreatment, substrate concentration and fermentation temperature on H-2 production using mesophilic seed sludge was undertaken. The results demonstrated that H-2 can be produced from both raw and ozonated POME, and the amounts of H-2 production were directly increased as the POME concentrations were increased. H-2 was successfully produced under the mesophilic fermentation of ozonated POME, with maximum H-2 yield, and specific H-2 production rate of 182 mL.g(-1) CODremoved (30,000 mg COD.L-1) and 6.2 mL.h(-1).g(-1) TVS (25,000 mg COD.L-1), respectively. Thus, indicating that the ozone pretreatment could elevate on the biodegradability of major constituents of the POME, which significantly enhanced yields and rates of the H-2 production. H-2 production was not achieved under the thermophilic and extreme-thermophilic fermentation. In both fermentation temperatures with ozonated POME, the maximum H-2 yield was 62 mL.g(-1) CODremoved (30,000 mg coD.L-1) and 63 mL.g(-1) CODremoved (30,000 mg COD.L-1), respectively. The highest efficiency of total and soluble COD removal was obtained at 44 and 37%, respectively following the mesophilic fermentation, of 24 and 25%, respectively under the thermophilic fermentation, of 32 and 20%, respectively under the extreme-thermophilic fermentation. The production of volatile fatty acids increased with an increased fermentation time and temperature in both raw and ozonated POME under all three fermentation temperatures. The accumulation of volatile fatty acids in the reactor content were mostly acetic and butyric acids. H-2 fermentation under the mesophilic condition of 37 degrees C was the better selection than that of the thermophilic and extreme-thermophilic fermentation. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.