Ethanol and Methane Production from the Organic Fraction of Municipal Solid Waste in a Two-Stage Process

Abstract

In the present study, the OFMSW was utilized for ethanol and methane production in a two-stage process. First, the OFMSW was fermented by adjusting different levels of total solids (10%, 20%, and 29%) and a yeast dose (6, 12, and 24 g/kgOFMSW) for bioaugmentation with Saccharomyces cerevisiae. A control treatment without bioaugmentation was used for benchmarking. In the self-fermentation of the OFMSW with its indigenous microbiota, lactic acid was mainly produced, followed by ethanol and acetic acid, where a maximum ethanol production of 113 ± 2 gCOD/kgTS, corresponding to 10.8 ± 0.4 g/L, at 20% of total solids was observed. The results showed that in all treatments with bioaugmentation, regardless of the content of total solids, the main metabolites were ethanol, lactic acid, and acetic acid, which represented more than 95% of the total metabolites. The ethanol concentration was increased by increasing the total solids and the yeast dose. The highest ethanol production was 407 ± 3 gCOD/kgTS with the bioaugmentation of 24 g/kgOFMSW and 20% of total solids, whereas the maximum ethanol concentration of 43.4 ± 0.1 g/L was obtained with bioaugmentation of 12 g/kgOFMSW and 29%. The methane potential of the raw OFMSW was 329 ± 5 NL-CH4/kgVS, whereas the solid digestates resulting from the fermentation exhibited similar or even higher methane yields than raw OFMSW. A maximum methane potential of 464 ± 2 NL-CH4/kgVS from the solid digestate obtained after fermentation of the OFMSW with bioaugmentation of 6 g/kgOFMSW of yeast and 10% of total solids was achieved. Thus, large amounts of ethanol and methane were achieved without the application of pretreatment and/or enzymatic hydrolysis, which implies a low-cost alternative for the production of biofuels.