A novel sequential ferrate–ultrasound strategy to improve methane recovery from lignocellulosic biomass

Abstract Potassium ferrate (PF) exhibits strong oxidative potential for lignocellulosic biomass pretreatment; however, its high cost and instability under alkaline conditions restrict large‐scale application. Likewise, ultrasonic pretreatment (UP), although effective in physically disrupting biomass, is energy intensive and unsuitable for substantial lignin degradation when applied alone. This study presents the first systematic investigation of the synergistic effects of PF and UP pretreatments, emphasizing the influence of application sequence on methane production and delignification efficiency. Three strategies were evaluated: UP followed by PF (UP → PF), PF followed by UP (PF → UP), and their simultaneous application (UP + PF), across varying PF dosages (0.333–0.999 mmol g −1 total solids). Among these, the UP → PF sequence achieved the best performance, yielding 37.9% lignin removal and methane production of 234.9 mL g −1 (volatile solids) – nearly a fivefold improvement compared with untreated controls. The enhanced outcomes are attributed to UP‐induced structural disruption, which increases surface accessibility, facilitating more effective lignin oxidation by PF. Methane production kinetics were successfully modeled using both the modified Gompertz equation ( R 2 = 0.9977–0.9995) and autoregressive integrated moving average (ARIMA) models ( R 2 = 0.9980–0.9999), with ARIMA demonstrating slightly superior predictive accuracy. These findings highlight the potential of optimized sequential PF and UP pretreatments as a novel strategy to enhance biomethane recovery from lignocellulosic waste, advancing the development of efficient and sustainable bioenergy systems.