Enhanced lactic acid production from the anaerobic co-digestion of swine manure with apple or potato waste via ratio adjustment

The valorization of organic waste into lactic acid (LA) via co-digestion has attracted tremendous research interests in recent years. This study investigated the feasibility of intensifying the LA accumulation from anaerobic digestion (AD) of swine manure (SM) by adding apple waste (AW) or potato waste (PW). Results indicated that AW or PW obviously enhanced the accumulation of LA, and when the optimal mixing ratio of AW or PW to SM of 75:25, the maximum concentrations of LA were 27.61 and 8.91 g COD/L, which were around 3.53and 1.14 folds of that of the mono-digestion of SM, respectively. Meanwhile, the co-digestion of SM and AW showed significantly higher LA production than that of SM and PW (p < 0.05). High reducing sugar content of AW contributed to LA accumulation in AD process. In addition, AW increased the relative abundance of Lactobacillus and Clostridium, thus benefited the production of LA.