Feasibility and benefits of methanogenesis under oxygen-limited conditions

Methanogenic and aerobic (or microaerophilic) biological processes are often considered mutually exclusive and separated as biological wastewater treatment options. However, under oxygen-limited conditions, both aerobic respiration and methanogenesis can be practically accomplished by a single mixed culture. This paper describes sustained batch culture, oxygen-limited methanogenic serum bottle and bench-scale systems. Serum bottle cultures exhibited methanogenic activity similar to or greater than that of a strictly anaerobic culture maintained in parallel. The COD removal efficiencies of anaerobic, oxygen-limited, and aerobic bench-scale reactors receiving 30,000 mg/l of sucrose were all greater than 93%, a system receiving 1 g O2/LR-day achieved a lower final effluent COD than the strictly anaerobic reactor. After a shock-load of sucrose, the pH recovered in low-aeration batch reactors in 28–34 days, whereas anaerobic pH did not recover after 52 days of observation. In the future, methanogenesis under limited-aeration may be employed as an energy efficient treatment option to achieve low final COD concentrations, minimal biosolids generation, and mineralization of a broad range of specific organic chemicals.