Microwave co-pyrolysis of industrial sludge and waste biomass: Product valorization and synergistic mechanisms

Microwave co-pyrolysis of textile dyeing sludge (TS) and furfural residue (FR) was investigated in this study. Comprehensive pyrolysis index (CPI) was employed to investigate pyrolysis performance and FR addition significantly improved co-pyrolysis. Product distribution showed that increasing FR ratio enhanced the bio-oil and gas with significant reduction in biochar. For bio-oil, FR addition neutralized the strong alkalinity and inhibited the formation of nitrogen compounds. Moreover, bio-oil maintained a very low oxygenates content (0.97-5.97%). For biochar, co-pyrolysis was favorable for the enrichment of C and H and mitigated the potential contamination. FR addition increased the calorific value and contributed to pore development of biochar. Online inspection displayed that co-pyrolysis drastically restrained the release of sulfur-compounds and nitrogenates in volatile, while enhanced the production of alkanes, aldehydes, and ketones. Moreover, the interaction between TS and FR was influenced by their major components. For heavy metals (HMs), Er was at low risk for most HMs and FR addition ratios of 40 and 80 wt% appeared to be more favorable. Principal component analysis (PCA) showed that FR addition changed the decomposition behavior and affected co-pyrolysis process. This study also evaluated the co-pyrolysis synergistic mechanisms of TS and FR. Overall, microwave co-pyrolysis is a novel and effective method to reduce environmental pollution and produce high-quality products, providing new insights for the low consumption and efficient utilization of industrial solid waste.