Anaerobic digestion (AD) of swine manure (SM) is often hindered by its slow biodegradation due to complex, poorly degradable organics, requiring long retention times for stable methane production. To address this limitation, this study investigated a low-dose co-substrate strategy to enhance the AD of SM. In the co-digestion ratio optimization test, methane yield improved by up to 5.5-fold compared to the SM-only condition (44 ± 1 mL/g COD), reaching 242 ± 12 mL/g COD at a 60:40 SM:food waste (FW) ratio, accompanied by stable pH (> 7.0) and high bicarbonate alkalinity (> 6,600 mg CaCO3/L). However, higher proportions of FW resulted in acid accumulation and process failure. In the trace FW addition test, small FW slurry additions (1–8 mL) significantly enhanced methane production, reaching up to 509 ± 30 mL, with a methane yield of 170 ± 9 mL CH4/g COD. COD removal efficiency increased from 63% to 81%, while dissolved organic carbon levels increased to 4,555 mg/L. Fluorescence excitation-emission matrix analysis confirmed elevated levels of soluble microbial products. Microbial analysis revealed enrichment of Bacteroides, Keratinibaculum, Methanothrix, and Methanosarcina, indicating synergy from trace substrate addition. These results demonstrate that minimal FW input can activate microbial metabolism and improve AD performance.
Kim et al. (Sun,) studied this question.