Factors affecting methane production and system recovery in mesophilic anaerobic digestion of food waste

Food waste (FW) has high production potential that can be converted into renewable energy in the form of biogas during anaerobic digestion (AD). Batch tests under mesophilic (37°) disgestion were performed to evaluate the effects of different dosage ratios (10-35%), salts (0-20 g·L-1) and oil content (0-20 g·L-1) on methane (CH4) production, process stability and organic reduction during the AD. The results showed that optimal CH4 occurred at a dosage ratio of 20%, while ratios > 30% caused inhibition. Salt (<5 g·L-1) enhanced AD efficiency, peaking at 314.75 mL CH4 production g VS-1 (1 g·L-1 salt), whereas > 15 g·L-1 salt suppressed methanogenesis. Oil at 15 g·L-1 maximized methane yield (393.66 mL CH₄ production g VS-1) with 12-day digestion, while 20 g·L-1 oil induced inhibition. Excessive organic loading rate (OLR) (>3.0 g VS/L/d) triggered the accumulation of Volatile Fatty Acids (VFAs) > 20,000 mg/L and an acidification pH = 5.94, collapsing biogas production; recovery via pH adjustment, starvation, and sludge inoculation reduced VFAs by 96-100%, restoring stable biogas output (0.63-2.09 L/L/d) with neutral pH = 7.35 and 65% methane content. Microbial synergy and VFA degradation ensured system resilience under safe OLR ≤ 3.0 g VS/L/d, highlighting FW's viability for renewable energy recovery.