Enhancing bioenergy Efficiency: Microwave-Assisted Co-pyrolysis of plastic and sludge waste with catalytic upgrading

The growing accumulation of plastic and sewage sludge (SS) waste necessitates effective and sustainable valorization technologies. This study presents a novel integration of microwave-assisted catalytic co-pyrolysis of polyethylene terephthalate (PET) and SS, offering a dual solution for waste reduction and bioenergy recovery. The research uniquely combines synergistic feedstock interaction, catalyst performance and comprehensive energy analysis within a microwave-driven system, an area seldom explored in previous literature. The effects of pyrolysis temperature, PET/SS feedstock ratio and catalyst type (HZSM-5 and KOH) were systematically investigated. HZSM-5 significantly enhanced bio-oil yield (up to 49.5 wt%) and bioenergy density (31.88 MJ/kg), while KOH promoted higher biochar yield (up to 70.05 wt%) with improved fuel stability. Catalyst addition also influenced product composition, increasing valuable compounds like ketones and aromatic hydrocarbons while modulating biogas profiles (CO and CO2). GC-MS and GC-TCD analyses validated the compositional changes. The study demonstrated bioenergy extraction efficiencies ranging from 36.74 % to 92.50 %, although overall process energy efficiency remained lower due to energy losses at the lab scale. Nonetheless, catalysts induce lower reliance on operating temperature, enabling lower-temperature operation and indicating potential energy savings in scaled-up systems. The use of microwave energy also offers rapid, selective heating with reduced startup times, which is advantageous for continuous industrial processes. This work highlights the added value of catalyst, microwave synergy for improving energy yields and product quality from heterogeneous waste. The insights gained provide a critical foundation for designing scalable, efficient microwave pyrolysis systems and advancing waste-to-energy technologies in support of a circular economy.