A NEW TWO-PHASE PROCESS FOR WATERLESS METHANE FERMENTATION TREATING THE ORGANIC FRACTION OF MSW

A newly developed high-rate methane production process for treating organic fraction of municipal solid waste (OFMSW) was introduced in this paper. This process is composed of three parts: mixing tank, thermophilic hydrolytic/acidogenic reactor (55 ºC), and mesophilic methanogenic reactor (35ºC). In this process, the shredded OFMSW is firstly mixed in the mixing tank with the digested sludge re-circulated from the methanogenic reactor for making fluid slurry. The slurry is then hydrolyzed in thermophilic acidogenic reactor to soluble organics such as acetate, propionate and lactate. Finally, the hydrolyzed slurry is 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 to 10 d. The OFMSW with a moisture content of 77% (TS 23%) was effectively degraded to biogas at a hydraulic retention time 12.5 d, corresponding to a COD loading rate of 30 kg COD 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 m 3 with methane content of around 60%.