Enhanced synergistic biogas production from co-blended niger seed husks and coffee husk via alkali-microbial pretreatment and iron(III) nanocatalyst augmentation in anaerobic digestion

Agricultural waste management and the demand for sustainable energy present a pressing global challenge. This study addresses this urgency by exploring the valorization of coffee and niger seed husks two abundant agro-industrial by-products for enhanced biogas production. The complex, recalcitrant structure of lignocellulosic biomass often limits its bioconversion efficiency, necessitating innovative pretreatment methods to improve its digestibility and overall yield. The current study investigated that a synergistic approach combining alkali bacterial pretreatment with an iron (III) nano catalyst would significantly boost biogas output. The pretreated husk blend was subsequently subjected to anaerobic digestion. Then, synthesized a stable iron (III) oxide nano catalyst from neem leaf extract and optimized the process parameters—substrate-to-inoculum ratio, pH, and catalyst concentration—using response surface methodology with a Box-Behnken Design. The optimization led to an impressive maximum biogas yield of 730.347 N mL g⁻¹ volatile solids with a high methane content of 65.951 %. This performance represents a 47 % greater biogas yield than untreated biomass, a 36.47 % increase compared to digestion without the nano catalyst, and a remarkable 61.64 % improvement over biomass digested without an inoculum. Thus, the study demonstrates a highly efficient and environmentally beneficial method for converting underutilized waste into a valuable energy resource and synergistic approach offers a clear path to commercial viability. • Pretreatment cut lignin and raised VS removal, boosting biodegradability. • Optimized mix yielded 730.347 N mL/g VS with ∼ 65.951 % CH₄ . • Fe(III) Nano-catalyst cut lag from 6→2 days ; CH₄ rate + 25 % . • Offers a sustainable route to valorize agro-industrial residues.