Mesophilic anaerobic co-digestion of pulp and paper sludge and food waste for methane production in a fed-batch basis

Co-digestion of pulp and paper sludge (PPS) and food waste (FW) in a batch-fed digestion system was conducted on a laboratory scale. Three reactors named A1, A2, and A3 were tested. PPS and FW mixed at different mass ratios of 1:3, 1:1, and 3:1, respectively, were loaded in the reactors. Bioconversion at high efficiency was obtained in the system. The accumulative methane yield of each reactor was 144mLg(-1)VSfed (A1), 256 mL g(-1) VSfed (A2), and 123 mL g(-1)VSfed (A3). The soluble chemical oxygen demand (COD) removal efficiencies reached 73.2% (Al), 93.9% (A2), and 79.6% (A3). A pH in the range 5.8-8.4 was obtained in the three reactors without adjustment due to the high buffer capacity of the mixing feedstock. No toxicity inhibitions of volatile fatty acids and NH3-N occurred in reactor A2. This study showed that it was good for co-digestion of PPS and FW in a mass ratio of 1:1 for methane production, which resulted in higher methane yield, a greater buffer capacity, a higher organics removal efficiency, and a more stable process.