Magnetite-modified attapulgite influencing methane production in anaerobic digestion of pig manure: Performance and mechanism

High ammonia nitrogen and a low electron transfer rate result in low methane production efficiency during the pig manure digestion. This study explored the impact of magnetite-modified attapulgite (MMA) on methane production in the anaerobically digested pig manure, and the mechanisms on MMA influencing methane production. The results indicated that low doses of MMA, with loadings ranging from 1.4 to 6.9 g/L, enhanced methane production, achieving values between 146.5 and 212.5 mL/g VS with MMA loadings of 1.4 to 6.9 g/L, increasing by 2.4 % to 33.5 % compared to the control. These low doses of MMA exhibited higher hydrolytic, acidogenic and methanogenic rates, as evidenced by the increase in β-glucosidase, dehydrogenase, and F₄₂₀ activities, along with a rise in hydrolytic bacteria and Methanosarcina which facilitates interspecies electron transfer. In contrast, higher doses of MMA decreased methane production by 1.6 % to 14.5 %. This was primarily attributed to high FA and iron reduction.