Effects of Operation Conditions on the Performance of the ASBR Methane Fermentation of Syrup Wastewater

Methane fermentation of the syrup wastewater was conducted using the anaerobic sequencing batch reactor (ASBR). Organic loading rate (OLR), which is calculated by dividing the substrate concentration in the wastewater by hydraulic retention time (HRT), was set at the same value in two runs; R1 with longer HRT and higher concentration of substrate, and R2 with shorter HRT and lower concentration of substrate. The effects of HRT and substrate concentration on the performance of the methane fermentation were tried to be elucidated by comparing two experimental runs. The OLR was increased stepwisely from 2.6 to 20.4 g-COD/L/d. No significant difference was observed until the OLR of 10.2 g-COD/L/d. After the OLR increased to 20.4 g-COD/L/d, oxidation reduction potential (ORP) in R2 with short HRT of 3.1 days increased immediately and methane gas production rate (MPR) decreased drastically. In contrast, the ORP of R1 with long HRT of 6.2 days was in the range from -450 to -350 mV, and high MPR was maintained for a while though the OLR in R1 was the same with that in R2. More than 10 days of operation with the OLR of 20.4 g-COD/L/d, however, the pH in R1 decreased abruptly and the MPR also decreased rapidly. It was revealed that the collapse of methane fermentation caused by the too short HRT occurred faster than that caused by the too high concentration of substrate.