Promote lactic acid production from food waste fermentation using biogas slurry recirculation.

It is a promising method to recover lactic acid from food waste (FW) fermentation, but the bottleneck problem is the low yield when using mixed inoculation. In this study, laboratorial biogas slurry (LBS) and industrial biogas slurry (IBS) were used as the additive in semi-continuous FW fermentation, aiming to promote the production of lactic acid. According to the research results, the addition of LBS or IBS promoted the production of lactic acid significantly from FW, especially carbohydrate, because it increased the pH values, maintained low OPR levels, and increased microbial number and diversity in the fermentation systems. IBS performed better than LBS because of higher pH, more diverse microbial community and more functional microorganisms. The best ratio of IBS to feedstock was 0.2, and the lactic acid yield reached 0.42 g/gVSadded. An excessively high dose would alter the fermentation pathways, reduce the ratio of lactic acid.