Intermittent air mixing enhances dry anaerobic co-digestion of pig manure solid fraction and wheat straw: Methane performance and machine-learning-guided parameter optimization.

Dry anaerobic co-digestion of pig manure solid fraction (PMSF) and wheat straw was optimized using biochemical methane potential assays, semi-continuous full-factorial operation, microbial profiling, and machine learning. The strongest substrate synergy occurred at a 50:50 total solids (TS)-based PMSF-to-straw ratio. Under matched organic loading rates (OLRs), intermittent air mixing at 33.3 mL L-1 min-1, applied once daily for 1 min, improved volumetric methane production rate by an average of 10.8 %, reduced propionate accumulation, and shifted volatile fatty acids toward acetate, whereas excessive air input weakened performance. Support vector regression using TS, hydraulic retention time, OLR, and air-mixing intensity showed the best cross-validated performance (R2 = 0.912; root mean square error = 0.101 L L-1 d-1). Feature analysis associated methane production primarily with OLR, acetate-related metabolic state, and selected microbial genera; the microbial model was interpreted as exploratory because of its small sample size. These findings define an operation window for data-driven optimization of high-solids agricultural-waste digestion.