An Integrated Pyrolysis Approach for Hydrogen Production and Microplastic Elimination from Sewage Sludge: Experimental and Analytical Perspectives

Abstract

Municipal sewage sludge, a byproduct of wastewater treatment processes, is increasingly recognized as a reservoir of microplastics (MPs), posing environmental risks to soil and water systems. This study evaluates pyrolysis as an integrated solution for recovering hydrogen-rich syngas and eliminating MPs from sewage sludge. The sludge, sourced from a wastewater treatment facility in the United Kingdom, was pre-treated through conditioning and drying before being thermochemically converted at 800 °C. Varying the auger speed revealed that slower speeds significantly improved hydrogen output, reaching up to 41 vol%, primarily due to extended gas residence time that favours secondary reforming and cracking reactions.Quantitative analysis of MPs showed a complete reduction, from an initial concentration of 53.7 ± 7.2 MPs/g in dried sludge to undetectable levels in the resulting biochar. Morphological characterization identified fragments (46.2%) and fibres (41.9%) as dominant MP types, with further evaluation of their size and colour profiles. FTIR spectroscopy confirmed the presence of polyethylene terephthalate (PET) in untreated sludge and the absence of plastic-related signals in post-pyrolysis samples. The results highlight pyrolysis as a promising method for concurrent clean energy recovery and microplastic remediation, offering practical guidance for advancing circular economy goals and sustainable waste-to-hydrogen pathways.