3.2. Comparison with previous studi

3.2. Comparison with previous studies of co-digestion of different substrates with food waste for methane production

Previous studies have also tested the effect of different co-substrates for the anaerobic digestion of food waste (Supplementary Table 1). Zhang et al. (2011) used co-substrates to provide supplemental trace elements for the anaerobic digestion of food waste and to increase methane production. Kim et al. (2003) optimized the mixing ratio of food waste with sewage sludge under mesophilic and thermophilic conditions. Other research indicated that pretreatment of food waste by microaeration increased the conversion of short chain fatty acids to acetate (Lim and Wang, 2013). The present paper is the first to describe the co-digestion of food waste with microalgal biomass. The results presented here indicated increased methane production when the substrate consisted of equal parts raw sludge, algal biomass, and food waste leachate. Further research is needed to assess the effect of different pretreatments of the microalgal biomass and the optimal mixing ratios of the three substrates. Also, the serial addition of different substrates may allow maintenance of a large population of methanogens during the whole digestion process and improve the methane yield