Effects of an iron oxide–zeolite additive on process performance of anaerobic digestion of swine waste at mesophilic, ambient and psychrophilic temperatures

Abstract

The effects of an additive termed as iron oxide–zeolite on the process performance of anaerobic digestion for treating swine waste at mesophilic (35 °C), ambient (25 °C) and psychrophilic (15 °C) temperatures were investigated. Significantly enhanced biogas and methane yields (20.90–183.03% and 33.84–221.52%, respectively), methane content (10.73–14.26%), VFA formation and utilization, and organic matter removal (e.g., 35.79–69.02% of VS removal) demonstrated the stimulating effects of the additive. The high adsorption capacity of the additive buffered the surrounding pH and reduced the ammonia concentration by about 380.35–510.73 mg L⁻¹, which suppressed ammonia inhibition at mesophilic temperature. The increased concentration of coenzyme F₄₂₀ indicated the strengthened methanogenic activity under all three temperatures. By supplementing the iron oxide–zeolite additive, net energy recoveries of the digestion processes increased by 183.04%, 33.14% and 21.80% at psychrophilic, ambient and mesophilic temperatures, respectively. The method for supplementing the iron oxide–zeolite additive is an advanced and feasible approach to achieve successful synthesis of biogas from AD by treating livestock waste, especially under ambient temperature in the winter seasons of Northern China.