Enhance the ethanol fermentation performance of kitchen waste using microwave pretreatment

Pretreatment is considered to be one of the key steps to improve the bioavailability and fermentability of kitchen waste (KW). In this article, microwave pretreatment was used for the enzymatic saccharification and ethanol fermentation of KW. The optimal pretreatment parameters were determined as mixing KW with water at a solid-to-liquid ratio (S/L) of 1:5 and pretreating at 19.2 W/g for 6 min. The obtained reducing sugar yield in the enzymatic hydrolysate of the KW pretreated by optimal parameters was 0.721 g/g TS. For separate enzymatic hydrolysis and fermentation (SHF), the final ethanol yield at 21 h using enzymatic hydrolysate of microwave-pretreated KW (MWKW) as substrate was 0.344 g/g TS (equivalent to 93.1% of the theoretical ethanol yield). It was 52.2% higher than that using the hydrolysate of un-pretreated KW as substrate. For simultaneous enzymatic hydrolysis and fermentation (SSF), the final ethanol yield generated from MWKW was 0.269 g/g TS, which was only 6.3% higher than that generated from un-pretreated KW. The microstructure of KW was observed using SEM, which indicated that the demulsification of lipid and the structural rupture of the starch granules and fibers under the effect of microwave would result in the rough and porous structures of MWKW and thereby improving the bioavailability and fermentability of KW. These results indicate that microwave pretreatment has the potential to increase the total ethanol production capacity of kitchen waste and is beneficial to the formation of a more economically feasible process for the bioethanol production from kitchen waste.