Anaerobic co-digestion of OFMSW and sewage sludge: Digestate valorisation into advanced CO2 capture materials

Optimizing the co-digestion of Sewage Sludge (SS) and the Organic Fraction of Municipal Solid Waste (OFMSW) remains a key challenge for improving biogas generation in waste-to-energy systems. This study investigates how SS: OFMSW mixing ratios affect anaerobic co-digestion (ACoD) performance and evaluates the conversion of the resulting digestate into advanced materials for CO₂ capture. The production of methane and biogas was measured in order to evaluate digestion kinetics. The AcoD of SS: OFMSW (50:50 w:w) allows methane production with maximum values of 448.5 NmL CH₄ /g VS similar to the yield obtained from OFMSW digestion, showing a good fitting with the modified Gompertz kinetic model. Co-digesting of OFMSW and SS improves the VS, COD_T and the C/N ratio of the SS digestion. The digestate and the biocarbons produced after pyrolysis were analysed in depth with XRD, XRF, N 2 adsorption-desorption, CO 2 adsorption-desorption isotherms, TGA-DTA and SEM to establish a relationship between the physico-chemical and CO 2 capture properties. The pyrolysis process was optimised at 500 °C for 180 min. Biocarbons were chemically activated with potassium hydroxide. The optimum biocarbon: KOH ratio was 1:1 allowing an improvement in the textural properties along with the CO 2 capture amount (849 μmol g -1 ). Finally, washing biocarbons with acid solution, favours the elimination of inorganic species and metallic iron, promoting the development of materials with micro-meso porosity with a clear impact on CO 2 adsorption capacity. Results provide insights into optimising AcoD for biogas production and demonstrate the feasibility of converting digestate into functional biocarbon for CO 2 adsorption. • Co-digestion (50:50) of OFMSW and Ss yields 448 NmlCH 4 gVS -1 (58% CH 4 ). • Biochar: KOH ratio 1:1 enhances micropore/external area ratio for CO 2 uptake. • Biochar with 628 m 2 g -1 surface area and 1,086 μmolg -1 CO 2 adsorption was produced. • Waste-to-energy plus CO 2 capture boosts resource efficiency and sustainability.