Optimization of biogas production with rice straw-derived biochar: Characterization, hormetic effects, and kinetics modelling

One of the drawbacks of anaerobic digestion (AD) is the slow process startup. This study evaluated rice straw-derived biochar (RSB) to accelerate the anaerobic co-digestion of paper waste (PW) and chicken manure (CM). Rice straw pyrolyzed at 550°C (RSB550) was characterized by SEM, EDX, BET, FTIR, CEC, and CHN analyses before supplementation. Different doses (0, 2, 4, 6, and 10 % w/v) were tested in a batch system co-digesting PW and CM (2:1) under thermophilic conditions (45°C) for 44 days. RSB550 exhibited a surface area of 23.5 m²g⁻¹ , a pore volume of 0.1 cm³g⁻¹ , a pore size of 15.4 nm, and a CEC of 2.0 meq/100 g, favorable for AD. Biogas yield was dose-dependent and significant via ANOVA, with 2 % RSB550 increasing production by 31.74 % compared to the control. Excess biochar reduced yield. Modified Gompertz modeling fit well (R²: 0.995–0.999), confirming biochar as a promising strategy for enhancing AD efficiency. • Biogas yield was optimized via co-digestion of paper waste, chicken manure, and rice straw biochar (RSB) as a supplement. • Biogas yield was dose-dependent with 31.74 % increase in overall biogas production with 2 % RSB. • Low RSB doses boosted microbial activity and biogas yield, while high doses reduced production, showing a hormetic biochar effect. • Non-linear regression of the modified Gompertz model showed strong fit to biogas data with R² values ranging from 0.995 to 0.999. • Utilization of biochar (at optimum dosage) accelerates biogas productivity.