The system performance in fed batch process compared to batch process in Fig 5 expressed the lower yield of biogas and methane in fed batch process. Regarding
to the same operated hydraulic retention time (HRT), the higher organic loading rate influenced to lower degradation
efficiency [17]. Since the biodegradation was not
completely taken placed, the methane producing bacteria could not convert volatile acid to become methane resulting
in a decrease in COD removal efficiency, lower the amount of gas, as well as the methane content [18]. This similar result was indicated that lower organic loading rate gave better biogas generation.