Kinetic study on the effects of elevated temperature and micro aeration in volatile fatty acids production by anaerobic fermentation of alkaline-pretreated oil palm empty fruit bunch

Abstract

This research studied the conversion of alkaline-pretreated oil palm empty fruit bunch (OPEFB) into volatile fatty acids (VFA) through anaerobic fermentation (AF). In AF, the methanogens that consume VFAs must be suppressed to increase the accumulated VFA as an intermediate product of AF. In-depth research has not been conducted on the effects of temperature and micro aeration to maximize the VFA accumulation. To investigate the temperature effect, the experiment was run at mesophilic (RM) and thermophilic conditions (RT). The impact of the micro aeration dose was studied in the thermophilic reactor set to the ORP −50 mV (RTM −50) and ORP −150 mV (RTM −150). The experimental data were fitted to the Anaerobic Digestion Model 1 (ADM 1) using AQUASIM®. The khyd.ch value of the RT reactor is higher than that of the RM, suggesting that high temperatures encourage hydrolysis and enhance hydrolase activity. Based on the simulation results, RT reactors without micro-aeration had a substantially higher specific growth rate of methanogens compared to RM. Therefore, micro aeration should be applied in RT to suppress the potentially faster growth of methanogen bacteria at elevated temperature. The result of this study indicated that both temperature and micro-aeration were important process variable to be further optimized to make VFAs production from OPEFB attractive.