Renewable energy production from organic wastes by high-solid methane fermentation

A newly developed high-rate methane production process for treating organic fraction of municipal solid waste (OFMSW) was introduced in this paper. This process was composed of three parts, mixing tank, thermophilic hydrolytic/acidogenic reactor (55°C), mesophilic methanogenic reactor (35°C). In this process, the shredded OFMSW was firstly mixed in the mixing tank with the digested sludge re-circulated from the methanogenic reactor for making fluid slurry. The slurry was then hydrolyzed in thermophilic acidogenic reactor to soluble organics such as acetate, propionate and lactate etc. Finally, the hydrolyzed slurry was converted to biogas in mesophilic methanogenic reactor. A bench-scale continuous experiment was conducted with shredded OFMSW by changing the retention time of the process from 30 days to 10 days. The OFMSW with a moisture content of 77% (TS 23%) was effectively degraded to biogas at a HRT reduced to 12.5 days, corresponding to a COD_Cr loading rate of 30 kg-COD_Cr·m^-3·d^-1, without adding dilution water. The experimental results demonstrated that the organic degradation efficiency was as high as 85%, and one ton of OFMSW produced biogas of 150 m³ with methane content of around 60%.