Effects of temperature and inoculation ratio on methane production and nutrient solubility of swine manure anaerobic digestion

This study investigated the effects of temperature and volatile solids (VS) ratio of feedstock to inoculum (F/I ratio) on methane (CH₄) production and the solubility of nitrogen (N), phosphorus (P), cooper (Cu), and Zinc (Zn) after anaerobic digestion (AD) of swine manure. The highest cumulative CH₄ yield of 470 L/kgVS_feed was obtained with F/I ratios of 2.0 and 3.0 with mesophilic (37 °C) temperature, and methane production rate decreased with the increase of F/I ratio. As F/I ratio increased from 0.5 to 4.0, the lag phase for methane production increased from 1.02 days to 13.52 days, indicating an initial inhibition at high F/I ratios. AD increased the concentrations of ammonia, Cu and Zn in the AD effluent supernatant, while decreased total and water extractive P concentrations. The changes of ammonia, Cu, Zn, and P concentrations were more significant with the increase of F/I ratio.