The effect of the labile organic fraction in food waste and the substrate/inoculum ratio on anaerobic digestion for a reliable methane yield

•The effect of labile organic fraction (LOF) in FW and S/I ratio on AD were examined.•LOF loading caused acidification and contributed to a high methane yield from FW.•The CH4 content had a significant relationship with pH but not VFAs concentration.•Low S/I ratio (<0.33) was required to obtain a reliable methane yield in AD of FW.

Influence of the labile organic fraction (LOF) on anaerobic digestion of food waste was investigated in different S/I ratio of 0.33, 0.5, 1.0, 2.0 and 4.0 g-VSsubstrate/g-VSinoculum. Two types of substrate, standard food waste (Substrate 1) and standard food waste with the supernatant (containing LOF) removed (Substrate 2) were used. Highest methane yield of 435 ml-CH4 g-VS−1 in Substrate 1 was observed in the lowest S/I ratio, while the methane yield of the other S/I ratios were 38–73% lower than the highest yield due to acidification. The methane yields in Substrate 2 were relatively stable in all S/I conditions, although the maximum methane yield was low compared with Substrate 1. These results showed that LOF in food waste causes acidification, but also contributes to high methane yields, suggesting that low S/I ratio (<0.33) is required to obtain a reliable methane yield from food waste compared to other organic substrates.