Biogas by two-stage microbial anaerobic and semi-continuous digestion of Chinese cabbage waste

Anaerobic digestion of Chinese cabbage waste was investigated through a pilot-scale two-stage digester at a mesophilic temperature of 37 °C. In the acidification digester, the main product was acetic acid, with the maximum concentration of 4289 mg·L− 1 on the fourth day, accounting for 50.32% of total volatile fatty acids. The oxidation reduction potential (ORP) and NH4+-N level decreased gradually with hydraulic retention time (HRT) of acidification. In the second digestion phase, the maximum methanogenic bacterial concentration reached 9.6 × 1010 ml− 1 at the organic loading rate (OLR) of 3.5–4 kg VS·m− 3, with corresponding HRT of 12–16 days. Accordingly, the optimal biogas production was 0.62 m3·(kg VS)− 1, with methane content of 65%–68%. ORP and NH4+-N levels in the methanizer remained between − 500 and − 560 mV and 2000–4500 mg·L− 1, respectively. Methanococcus and Methanosarcina served as the main methanogens in the anaerobic digester.

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