Enhanced anaerobic fermentation with wheat stalk activated carbon for methane generation

• Optimal preparation conditions significantly enhance methane production • Orthogonal experiment identifies key influencing factors • Nonlinear relationship between biochar specific surface area and methane production • Biochar shortens lag phase, stabilizes pH, and promotes cell wall degradation To enhance the management of agricultural waste and promote its resourceful utilization, this study investigates the enhancement of methane production from wheat straw anaerobic digestion using KOH-activated biochar derived from wheat stalks. An orthogonal experimental design (L9(3⁴)) was employed to optimize the biochar preparation by examining four key parameters: activation time (30-90 min), KOH impregnation ratio (1:2-1:6), activation temperature (600-800°C), and pickling cycles (1-3). The optimal preparation condition was identified as an activation time of 30 minutes, an impregnation ratio of 4, an activation temperature of 800°C, and 2 pickling cycle. Fermentation results demonstrated that the addition of this optimized biochar significantly improved performance. The amended system (Group E) achieved the highest cumulative methane production of 2,613.79 mL, representing increases of 15.8% and 24.5% compared to the control group (without biochar) and the blank group, respectively. Biochar addition accelerated the process, advancing the daily methane production peak by 1-4 days and shortening the kinetic lag phase (from ∼5.8 days in controls to as low as 3.97 days). Furthermore, it increased the average methane content by up to 19.73% and effectively buffered pH fluctuations during the acidogenic phase, creating a more stable environment for methanogens. The enhancement is attributed to the biochar's porous structure and high specific surface area, which provide microbial attachment sites, facilitate mass transfer, and improve system buffering capacity. This research confirms wheat stalk-derived biochar as an effective additive for optimizing methane production and process stability in the anaerobic fermentation of lignocellulosic biomass.