A Novel Adsorption/Co-Digestion/Pyrolysis Scheme for Potato Peel Waste Management to Fulfill the Sustainable Development Goals (SDGs)

While several studies have utilized potato peel to prepare biochar involved in dye adsorption from wastewater, there is still a research gap in managing the spent feedstock to minimize secondary pollution formation. Hence, this study focuses on recycling the exhausted potato peel-based biochar after methylene blue (MB) adsorption for dual biogas and char production. Biochar was synthesized from potato peel pyrolysis (at 600 °C for 2 h) and employed for MB removal according to Box–Behnken statistical design. The optimized time and adsorbent dosage were 55.2 min and 2.6 g/L, giving 81.76 ± 4.34% removal at initial MB = 50 mg/L and pH = 9. The exhausted biochar was regenerated and supplemented to an anaerobic digester using a biochar: chicken droppings (CD) ratio of 1:4 (w/w) at 37 °C for 25 days. The biochar/CD synergy exhibited a bio-CH₄ yield of 159.6 ± 10.5 mL/g COD_initial greater than the sole CD digester by 32.4%. Another experiment was introduced to maintain a sustainable circular economy by thermally treating the anaerobic digestate at 500 °C for 60 min. The generated biochar acquired a yield of 0.62 g/g sludge-cake, exhibiting heterogenic surface and 52% carbon content. This novel adsorption/digestion/pyrolysis strategy enjoyed carbon credit and biogas/biochar selling, getting a 5.62-year payback period.