Enhancing methane recovery from food waste using walnut shell biochar and garbage enzymes

The study investigates the individual and combined effects of walnut shell-derived biochar (WSBC) and garbage enzyme (GE) on the anaerobic digestion of food waste, with a focus on methane recovery. WSBC was tested at concentrations of 5, 10, 15, and 20 g/L, and GE at volumetric concentrations of 5%, 10%, 15%, and 20% (v/v), followed by combined application at optimal doses. WSBC addition exhibited a dose-dependent response, with 15 g/L identified as the optimal, improving methane yield and stabilizing digestion, while higher loading (20 g/L) caused performance inhibition. GE enhanced the hydrolytic and acidogenic stages, significantly increasing cumulative biogas production; however, methane yields plateaued beyond 15% (v/v) dosage, and low GE dosages induced transient acidification. Individually, 15% (v/v) GE improved methane yield by 15.3% compared to the control, whereas WSBC (15 g/L) achieved a 6.0% increase. The combined application (15% (v/v) GE + 15 g/L WSBC) demonstrated a synergistic effect, yielding 24.7% higher methane yield (606.7 ± 27.6 mL/g VS), although diauxic patterns were observed. The results demonstrate that WSBC stabilizes methanogenesis while GE accelerates substrate hydrolysis, and their optimized integration provides an effective, low-cost strategy for enhancing renewable energy recovery from food waste within a circular economy framework.