Strategy to enhance semi-continuous anaerobic digestion of food waste by combined use of calcium peroxide and magnetite

Abstract

Optimizing methane production from food waste (FW) efficiently is always a hot topic in the field of anaerobic digestion (AD). In this study we aimed to improve the conversion of organics to methane by using CaO2 and magnetite to enhance the semi-continuous AD of food waste. Under the organic load of 2.5 g VS/L·d−1, the specific methane yield was increased from 333.9 mL CH4/g·VS to 423.4 mL CH4/g·VS by adding 0.01 g/L CaO2 with 0.4 g/L magnetite, improving the production of methane from FW. We assessed reactor performance, ORP changes, mass balance, enzyme activities and characterized the metagenomic profile of microorganisms involved in digestion. These microorganisms showed rapid conversion of volatile fatty acids and increased expression of genes related to hydrolysis and acid production. Thus, the addition of CaO2 and magnetite optimized the relationship between fermentation bacteria and methanogenic archaea to enhance the overall production of methane. Microorganisms evolved unique adaptive mechanisms in the co-operative environment of CaO2 and magnetite, as their energy metabolism patterns combined those controlled by individual CaO2 and magnetite addition. This method of combining a micro-aeration environment with conductive materials provides a new perspective for optimizing the AD of FW.