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.