Comparison of two anaerobic coupled systems for biomethanization of the organic fraction of municipal solid wastes

Abstract

Two lab-scale mesophilic systems for the anaerobic digestion of the organic fraction of municipal solid wastes (OFMSW) were compared. One system (RE-RE) consisted of two coupled reactors packed with OFMSW and the other (UASB-RE) consisted of an upflow anaerobic sludge blanket reactor (UASB) coupled to a packed reactor For the start-up phase, both leading reactors RE 1.1 and UASB 2.1 were inoculated with a mixture of non-anaerobic inocula and worked with leachate and effluent full recirculation. Once a full methanogenic regime was achieved in the leading reactors, their effluents were fed to fresh packed reactors RE 1.2 and RE 2.2. RE 1.1 reached its full methanogenic regime after 118 days (TMF time to achieve methanogenesis). At this point, its leachate had pH 7.05, alpha factor 0.35, volatile organic acids (VOA) 1405 mg/l HAc, COD 3080 mg/l and 62.02% methane in the biogas. The other leading reactor (UASB 2.1) reached its full methanogenesis regime after 34 days, and its effluent had pH 7.13, alpha 0.36, VOA 1289 mg/l HAc, COD 2280 mg/l, and 60.40% methane in the biogas. After coupling the leading reactors to the corresponding packed reactors, both coupled anaerobic systems showed similar performances regarding the degradation of OFMSW The UASB-RE system showed a faster overall start-up, a slightly higher reduction of organic matter (as volatile solids, VS) of the packed OFMSW and a higher biogas production than RE-RE. Removal efficiencies of VS and cellulose, and the methane pseudo yield were 85.95%, 80.88% and 0.1091 CH4/g-VSfed in RE-RE, and 88.75%, 82.61% and 0.1151 CH4/g-VSfed in RANMAL-RE.