Comparing operational characteristics of anaerobic methanogenic fermentation in CSTR system under two different start-up conditions

As anaerobic methanogenic bacteria are particularly sensitive to environmental habits and grow slowly, successfully devising a quick start-up for anaerobic digestion reactors has been a topic for research. In this study, we compared the operational characteristics of anaerobic methanogenic fermentation in a continuous-flow stirred tank reactor (CSTR) system, in two different starting conditions. The aim was to explore the suitable conditions and regulatory methods for treating molasses wastewater by a CSTR. After inoculating the excess sewage sludge from a brewery wastewater treatment plant, the CSTR process was started with an influent of 4 000 mg·L^-1 COD, and with the HRT being 18 h at 35℃. After operating for 103 days, the VFAs had accumulated in the reactor and the anaerobic methanogenic bacteria were inactive, suggesting that an efficient anaerobic microbial community was not present. However, when the HRT was maintained at 18 h, and the CSTR process was started by a stepwise increase of the influent COD to 4 000 mg·L^-1, the methanogenic bacteria in the CSTR were active and it could be enriched and cultured effectively. The COD removal efficiency reached 56% during an operational period of 65 days, which indicated that a highly efficient anaerobic microbial community had been constructed successfully.