Biogas production from municipal solid wastes using an integrated rotary drum and anaerobic-phased solids digester system

This research was conducted to develop an integrated rotary drum reactor (RDR)-anaerobic-phased solids (APS) digester system for the treatment of municipal solid waste (MSW) to produce biogas energy and achieve waste reduction. A commercial RDR facility was used to provide a 3-d pretreatment and sufficient separation of the organics from MSW and then the organics were digested in a laboratory APS-digester system for biogas production. The organics generated from the RDR contained 50% total solids (TS) and 36% volatile solids (VS) on wet basis. The APS-digester was started at an organic loading rate (OLR) of 3.1 gVS L−1 d−1 and operated at three higher OLRs of 4.6, 7.7 and 9.2 gVS L−1 d−1. At the OLR of 9.2 gVS L−1 d−1 the system biogas production rate was 3.5 L L−1 d−1 and the biogas and methane yields were 0.38 and 0.19 L gVS−1, respectively. Anaerobic digestion resulted in 38% TS reduction and 53% VS reduction in the organic solids. It was found that the total VFA concentration reached a peak value of 15,000 mg L−1 as acetic acid in the first 3 d of batch digestion and later decreased to about 500 mg L−1. The APS-digester system remained stable at each OLRs for over 100 d with the pH in the hydrolysis reactors in the range of 7.3–7.8 and the pH in the biogasification reactor in 7.9–8.1. The residual solids after the digestion had a high heating value of 14.7 kJ gTS−1.