ganisms in the absence of oxygen. The AD system has been widely applied in the environmental management of wastewater sludge, municipal solid waste, and livestock manure, with the primary objective of waste reduction. The produced biogas as renewable energy can also improve the operational profitability, reduce the greenhouse gas (GHG) emission, and mitigate climate change (Coats et al., 2013). It is reported that more than 2000 AD plants are currently operated in the United States to produce biogas, and an additional 11,000 sites could be developed in the future, which in total could provide power supply for over 3 million households and reduce between 4 and 54 million metric tons CH4 equivalent of GHG emissions by 2030 (USDA et al., 2014). Parawira et al. (2007) compared the biogas production from PPW using two-stage digesters with mesophilic and thermophilic configurations, and results showed that higher CH4 yield was obtained under mesophilic condition.
In this study, we investigated the feasibility of biogas production using PPW-FR as feedstock with different solid loadings to explore the suitable condition. The raw PPW without lactic acid fermentation was also employed in batch AD process as comparison.