Valorization of food waste and economical treatment: Effect of inoculation methods

Abstract

We evaluated cost-effective food waste (FW) treatment and synthesis of volatile fatty acids (VFA) using a leach bed reactor (LBR) operated at neutral pH and room temperature to maximize the profit from recovered products. Three inoculation strategies that include (1) inoculum pretreatment, (2) pretreatment plus leachate recycle, and (3) sole leachate recycle were examined and LBR performance was compared in these inoculation conditions. The inoculation method influenced the hydrolysis of FW in the LBR. Hydrolysis yield was as high as 771 ± 4 g cum.sCOD/kg VSadded with the second inoculation method only in a short reaction time of 6 d. Butyric and acetic acids consistently dominated VFA, and the LBR achieved the highest VFA yield of 649 ± 13 g COD/kg VSadded in the second inoculation. Bacterial community dynamics targeting 16S rRNA gene suggested that Roseburia would be the key player to fermentation of slowly biodegradable FW (e.g., fibers), while multiple types of bacteria affiliated with Enterobacteriaceae, Lactococcus, and Bacteroides mainly fermented FW to butyric and acetic acids at initial phase. The operating cost for FW treatment was calculated $88.1-$126.8 per ton of VSadded in the LBR. This study suggests that LBRs can economically stabilize FW only in 6 d without regular inoculation of exogenous microorganisms, along with high VFA recovery.