its lactic acid fermentation residue (PPW-FR) for methane (CH4) production. The experimental results showed that about 60–70% CH4 content was obtained. The digester using PPW-FR as feedstock exhibited better performance and produced a highest cumulative CH4 production of 273 L/kg VSfed, followed by 239 L/kg VSfed using PPW under the same conditions. However, with increasing solid loadings of PPW-FR feedstock from 6.4% to 9.1%, the CH4 production was inhibited.