Assessment of high-solid mesophilic and thermophilic anaerobic digestion of mechanically-separated municipal solid waste

Mechanically-sorted organic fraction of municipal solid waste (OFMSW) was tested to determine its biogas and biomethane generation efficiency. Methane production capability of OFMSW was examined in biochemical methane potential (BMP) tests. The factors affecting the high-solid anaerobic digestion (AD) of feedstock were investigated in a series of long-term semi-continuous digestion tests performed at dry mesophilic and thermophilic conditions in a continuously rotating drum reactor with working volume of 0.013 m3. OFMSW presented low biogas and methane generation capacity due to its contained non-biodegradable components and the low proteins and starch proportions. Dry mesophilic AD allowed only a relatively limited fraction of OFMSW volatile solids to be consumed for biogas and methane production. Reducing particle size favoured utilization of higher proportions of the available digestible organic substances, and concurrently promoted biogas and biomethane generation rate. Stability of methane generation was also significantly improved by particle downsizing. Small particles compensated the limited mass transfer and restricted distribution of methane production intermediate metabolites caused by water absence in the dry AD system. Dry thermophilic AD converted sufficient quantity of OFMSWs biodegradable content. The average methane released from dry thermophilic AD (0.176 m3kgVS−1) was higher than that of dry mesophilic AD of fine particles (0.148 m3kgVS−1) and much higher than that of dry mesophilic AD of same grain size (0.114 m3kgVS−1). High temperature proved more suitable for anaerobically digesting mechanically-sorted OFMSW. •OFMSW was subjected to high-solid anaerobic digestion.•Particle size reduction promoted methane generation rate and release.•Fine grains provided higher methane production stability to dry mesophilic AD.•Thermophilic process allowed valorisation of more organics in methane generation.•Dry thermophilic AD proved more sufficient in converting OFMSW to methane.