Deciphering the inhibition mechanisms of microplastics on the full-stage sludge anaerobic digestion via enrichment to anaerobic microbes and toxicity of released compounds

• Published in: Journal of hazardous materials 2024-12, Vol.485, p.136856, Article 136856
• Main Authors: Zhang, Zixuan, Liu, Peng, Zhang, Taishuo, Li, Kai, Wu, Xiaowei, Qiang, Hong, Jia, Hanzhong, Zhu, Lingyan
• Format: Article
• Language: English
• Subjects: Anaerobic microorganism; Dissolved organic compounds; Microplastics; Reactive oxygen species; Sludge treatment
• ISSN: 0304-3894; 1873-3336; 1873-3336
• DOI: 10.1016/j.jhazmat.2024.136856

Increasingly accumulated microplastics (MPs) in sludge could affect the sludge treatment process, while the contributions and mechanisms of MP particles and the released organic matters (MP-DOM) are not fully understood. To fill this gap, this study systematically investigates the effects and mechanisms of MPs on sludge anaerobic digestion. In the presence of MPs, the hydrolysis and acidogenesis of organic matters and methanogenesis all decreased due to the inhibition on the activity of anaerobic microorganisms and key enzymes. Mechanism analysis showed that MPs mainly acted as substrates to enrich anaerobic microorganisms and reduced the abundance and function of free microorganisms in sludge that metabolized organic matters. Moreover, a large amount of organic compounds including various plasticizers (dibutyl phthalate) and chain-scission products (benzoic acid) from physical abrasions of MPs with sludge particles, which made a 50.9–51.6 % contribution to the MP-inhibited sludge anaerobic digestion by the chemical toxicity and generated reactive oxygen species. Owing to the decreased digestion performance, the risk associated with ARGs and pathogenic bacteria increased distinctly. The findings highlight the concerns about MP-derived organic compounds compared to the substrate themselves and suggest the necessity for removing MPs in the sludge of wastewater treatment plants (WWTP). [Display omitted] •Microplastics (MPs) inhibited the performance of anaerobic digestion of sludge.•Anaerobic microbes lose their original function due to enrichment on the surface of MPs.•MP-derived organic matter (MP-DOM) with toxic additives mainly caused inhibition.•MP-DOM induced ROS production and chemical toxicity on anaerobic microbes.•MPs increased the propagation risk of ARGs and pathogen in sludge.