Integrated co-digestion and dual fixed-bed Fe2O3/Ca(OH)2 biogas upgrading using fruit and vegetable waste and cattle manure

Low-cost biogas upgrading remains a major barrier to decentralized biomethane deployment, particularly where conventional scrubbing or membrane systems are impractical. This study quantifies the performance envelope of a dual fixed-bed upgrading train operated in series (Fe 2 O 3 for H 2 S removal followed by solid Ca(OH) 2 for CO 2 capture) while treating real biogas generated on-site. Semi-continuous co-digestion of fruit and vegetable waste and cattle manure (30:70 on a VS basis) was used solely as a realistic and stable biogas supply to provide representative CH 4 /CO 2 /H 2 S loads to the upgrading unit. Under favorable hydrodynamic conditions, biomethane-quality enrichment was achieved (CH 4 ≥ 99.4%) with near-complete CO 2 removal (∼99.7–99.95%) and H 2 S reduced to low-ppm/sub-ppm levels (0.624–1.54 ppm; >99%). Performance losses at higher throughput indicated that CO 2 capture in the Ca(OH) 2 bed is the limiting step under demanding conditions. Post-use characterization (SEM, TGA/DTG, XRD) confirmed carbonation of Ca(OH) 2 to CaCO 3 and transformations consistent with sulfide capture in the iron bed, linking performance trends to sorbent evolution. System-level indicators yielded 66 m 3 biogas·t −1 and 44.22 m 3 CH 4 ·t −1 (≈1583 MJ t −1 , LHV basis) and a simplified benefit of ≈0.895 t CO 2 eq t −1 avoided within the defined boundary. The results demonstrate that biomethane-quality upgrading can be achieved under mild operating conditions using low-cost solid sorbents in a compact fixed-bed train. • Integrated semi-continuous AD plus dual fixed-bed upgrading using real biogas. • Biogas rate up to 66.44 NmL gVS −1 d −1 ; CH 4 increased to 66.94%. • BioCH 4 achieved with CH 4 up to 99.8% (v/v), CO 2 ≈ 0%, and H 2 S ≈ 0 ppm. • SEM/TGA/XRD confirmed Fe–S formation and Ca(OH) 2 carbonation to CaCO 3 . • System metrics with 1583 MJ t⁻¹ recovered energy and 0.895 t CO₂eq avoided·t⁻¹.