Optimizing Methane Production from Lignocellulosic Biomass: Low-Temperature Potassium Ferrate Pretreatment via Response Surface Methodology

Lignocellulosic biomass like pistachio shells (PSs) is a promising feedstock for anaerobic digestion (AD), but lignin recalcitrance limits biodegradability. Conventional pretreatments suffer from high energy costs or inhibitor formation; here, potassium ferrate (PF) + low-thermal pretreatment offers a green alternative. A Box–Behnken Design was employed to optimize the PF dosage, pretreatment temperature, and time, with response variables including the methane (CH4) yield, soluble chemical oxygen demand (SCOD)/total chemical oxygen demand (TCOD) ratio, and lignin removal efficiency. The optimized conditions (0.637 mmol/g total solids PF dose, 66.76 °C, 55.84 min) achieved a CH4 yield of 171.00 mL CH4/g volatile solids, representing a 4.3-fold increase compared to untreated PSs. The ANOVA results showed strong links between how much lignin was removed, the ratio of SCOD to TCOD, and the amount of CH4 produced, with the interactions between temperature and time being the most important. This study highlights the potential of PF-based pretreatment as a cost-effective and environmentally sustainable strategy to maximize CH4 yields from lignocellulosic waste, supporting renewable energy adoption and circular economy principles. Further studies should explore scalability and economic feasibility for industrial applications.