The effects and underlying mechanisms of composting and extrusion pretreatment on anaerobic biogas production from wheat straw

The effects of moisture + extrusion and composting + extrusion treatments on the production of biogas from the anaerobic digestion (AD) of wheat straw (WS) were systematically investigated. The results showed that when the moisture content of WS was adjusted to 55% before extrusion and maintained for 24 h, the biogas production of both the unextruded and extruded samples reached the highest levels, which were 130.48 and 158.41 mL/g, respectively. Based on these results, the WS was further aerobically composted after adjusting its moisture content to 55%, and then extruded for biogas production. The biogas production of unextruded WS initially increased and then decreased, reaching the maximum of 129.40 mL/g when the composting temperature rose to 55°C. In contrast, the biogas production of extruded WS increased at all composting temperatures and reached the maximum of 150.83 mL/g at 55°C, which is 19.49% higher than the initial biogas production of extruded WS at the start of composting. Mechanistic analyses indicated that extrusion reduced particle size, increased specific surface area, and disrupted lignocellulosic structure, while composting promoted partial degradation of hemicellulose and lignin. These structural modifications enhanced substrate accessibility and microbial degradation, thereby boosting biogas production. In conclusion, the combination of composting and extrusion pretreatment can significantly improve the biogas production performance of anaerobic digestion of WS, with an increase ranging from 20.76% to 43.45%, which is worthy of further research.