Energy recovery and waste treatment using the co-pyrolysis of biomass waste and polymer

Abstract

The pyrolysis of spent coffee grounds (SCG) and polymers was examined as a waste treatment option for energy recovery and carbon sequestration. Rice straw–derived biochar was used as control biochar to evaluate the sorption capacity and energy production capability of SCG-derived biochar. SCG are characterised by high levels of volatile matter, rendering them suitable as an energy source. SCG were converted to biochar, bio-oil, and syngas via pyrolysis, with yields of 22%, 33%, and 45%, respectively. The high heating value (HHV) of the biochar and bio-oil was 20.6 and 22.9 MJ kg⁻¹, respectively, indicating that they could be used as supplementary fuels. Co-pyrolysis with polymers (20 v v%⁻¹) increased the HHV of biochar. Accordingly, the maximum production of CH₄ and H₂ increased from 0.3 and 0.04 mmol g⁻¹ to 3.4−6.3 and 0.8−1.3 mmol g⁻¹, respectively. Polystyrene most strongly enhanced the yields of CH₄ and H₂, followed by polypropylene and polyethylene; this order was likely to be in accordance with the number of carbon and hydrogen atoms present in the monomers. Similar to rice straw–derived biochar, the biochar produced from SCG demonstrated a high sorption capacity for 2,4-dinitrotoluene and chromate due to its high carbon content and anion exchange capacity, respectively. Laboratory pot tests revealed that the coffee grounds–derived biochar was able to increase the growth of young radish. Our results suggest that the pyrolysis of SCG and polymer may be a promising option for waste treatment, energy production, and carbon sequestration.