Silage of the organic fraction of municipal solid waste to improve methane production

Abstract

The silage of the organic fraction of municipal solid waste (OFMSW) is a common practice in biogas plants. During silage, fermentation processes take place, affecting the later methanisation stage. There are no studies about how OFMSW silage affects methane production. This work aimed to determine the effects of silage (anaerobic acid fermentation) at different solids concentrations and temperatures on methane production. OFMSW was ensiled at 20, 35, and 55 °C with total solids (TS) concentrations of 10, 20, and 28% for 15 days. The ensiled OFMSW was then tested for methane production at the substrate to inoculum ratios (S/I) of 0.5, 1.0, and 1.5. Independently of the temperature, the production of the metabolites during silage increases with decreasing solids concentration. The highest production was of lactic acid, ethanol, and acetic acid, representing together 95% of the total. Methane production from ensiled OFMSW at 10% solids concentration shows, under every tested condition, better methane production than from fresh OFMSW. Ensiled OFMSW produces more methane than fresh OFMSW, and methane production was highest at 35 °C. HIGHLIGHTS Ensiling OFMSW allows a better methane recovery than fresh OFMSW.; Temperature and substrate-adapted inocula are essential for methanisation.; Lower solids concentration allows higher acidification rates.; Lactic acid and ethanol are the main products from OFMSW fermentation.; Methanisation under mesophilic conditions is better from ensiled than from fresh OFMSW.;

Keywords

• anaerobic digestion
• fermentation
• methane production
• ofmsw
• silage