Mechanistic insights into sludge inorganics suppressing methane yield through organic-inorganic interactions during anaerobic digestion.

High inorganic content poses a significant challenge to the anaerobic digestion of sludge. This study elucidates the impact of sludge inorganics on anaerobic digestion by correlating the binding mechanisms with the biodegradability of organics. The results show that sludge inorganics (SiO, FeCl, FeO, AlO, AlSiO, and metal carbonates) have good acid-base buffering capacity and can provide a stable acid-base environment for microorganisms. However, small particle size organics enter the pores of minerals, adhere to sludge inorganics, and undergo hydrogen bonding, van der Waals forces, ligand exchanges, Ca bridging, and electrostatic interactions with inorganics, making it more difficult for microorganisms to utilize. Inorganics can also obstruct electron transfer between microorganisms, leading to a 42.1 % ± 1.5 % decrease in cumulative methane production and a 54.6 % ± 5.7 % decrease in methane production rate during anaerobic digestion. The study elucidates the effect of sludge inorganics on anaerobic digestion, thus providing theoretical guidance for subsequent enhancement of anaerobic digestion efficiency.