Effect of magnetite powder on anaerobic co-digestion of pig manure and wheat straw

This study investigated the effects of different amounts of magnetite powder (i.e., 0 g, 1.5 g, 3 g, 4.5 g, 6 g) on the anaerobic co-digestion of pig manure (PM) and wheat straw (WS). The variations in pH, alkalinity, cellulase activity (CEA), dehydrogenase activity (DHA) and methane production, were analyzed by phases. Correlation of the activities of the two enzymes with methane production was also analyzed, and the Gompertz model was used to evaluate the efficiency of anaerobic digestion (AD) with the addition of magnetite powder. The results showed that magnetite powder had significant effects on the anaerobic co-digestion of PM and WS. The maximum total methane production with the addition of 3 g of magnetite powder was 195 mL/g total solids (TS), an increase of 72.1%. The CEA and DHA increased with magnetite powder in the ranges of 1.5-4.5 g, 1.5-6 g, respectively, while the methane production showed a better correlation with DHA than with CEA. Using the Gompertz model, the efficiency of AD was optimal when adding 3 g magnetite powder, with higher methane production potential (206 mL/g TS), shorter lag-phase time (14.9 d) and shorter AD period (44 d).