Investigating the potential of utilizing biogas solid digestate pellets of a biogas plant operating on chicken manure as solid biofuels and activated carbon

This study examines the potential for producing biofuel and activated carbon from the solid digestates of a biogas plant operating on chicken manure. The biogas plant with a capacity of 7MW, annually produces 45,000 tons of solid digestates. The solid digestate pellets was evaluated against international quality criteria for fuel pellets. The pellets, pre-treated with torrefaction as an enhancement to biofuels fuel properties were experimentally investigated by combustion in a large-scale fluidized bed boiler. Optimal torrefaction conditions were determined to be 60 minutes at 290°C, based on the higher heating value. Torrefaction nearly altered all of the biofuel properties. Despite some were improvements, raw and torrefied, the solid digestate pellets failed quality conformity tests. So as an alternative waste valorization process focusing on the production of activated carbon was investigated. The initial material, with a BET surface area of 4.49 m²/g, was impregnated with 1N ZnCl₂, KOH, and H₃PO₄ for 72 hours and converted to activated carbon through thermal activation. The resulting surface areas were 582.76 m²/g, 457.31 m²/g, and 0.68 m²/g, respectively. Initially, the material had no iodine and methylene blue numbers, it achieved iodine numbers of 1759.9 mg/g, 1295.4 mg/g, and 0.68 mg/g, and methylene blue numbers of 318.1 mL/g, 260 mL/g, and 3.3 mL/g for ZnCl₂, KOH, and H₃PO₄ treatments, respectively. The most successful chemical activation was achieved with ZnCl₂, yielding the highest improvements. The carbon content was 36.45%, increased to 70.37%. Therefore, the production of activated carbon using ZnCl₂ as the activating agent was successfully completed.