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Beyond simple inhibition: Unveiling the non-monotonic impact and multi-level mechanisms of aged microplastics on sludge anaerobic digestion
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Researchers used plasma treatment to precisely control polypropylene microplastic aging and tested its effects on anaerobic sludge digestion, finding that while unaged microplastics strongly inhibited methane production, optimally aged microplastics at a carbonyl index of 0.219 recovered methane yield to 83%.
Polypropylene microplastics (PP-MPs) in waste activated sludge (WAS) pose challenges to anaerobic digestion (AD), yet the impact of their aging degree is poorly understood. This study employed plasma treatment to precisely control PP-MPs aging, investigating their effects on WAS AD performance and underlying mechanisms. Unaged PP-MPs significantly inhibited methane production (38 % of control). However, aging remarkably alleviated this, exhibiting a novel non-monotonic relationship: optimal mitigation occurred at a carbonyl index (CI) of 0.219, recovering methane yield to 83 %. Mechanistically, this optimal aging enhanced hydrolysis and acidogenesis (improved kinetics, organic degradation, short-chain fatty acid (SCFA) production) and favorably shifted microbial communities (e.g., promoting hydrolytic/acidifying bacteria (Bacteroides), favoring hydrogenotrophic methanogenesis (Methanobacterium)). Crucially, these benefits were linked to enhanced cellular viability and mitigated oxidative stress (reduced reactive oxygen species (ROS), increased glutathione (GSH), restored cell integrity in sludge and Escherichia coli models). These multi-level non-monotonic responses precisely correlated with changes in PP-MPs' surface properties (hydrophilicity, zeta potential, crystallinity, nitrogenous functional groups), all peaking at CI = 0.219, which modulated microbial interactions. This study provides unprecedented mechanistic insights into the complex non-monotonic impact of PP-MP aging on WAS AD. Our findings underscore the critical importance of considering MPs' specific aging degree for environmental risk assessment and optimizing AD processes.
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Inhibition of aged microplastics and leachates on methane production from anaerobic digestion of sludge and identification of key components
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Researchers investigated the effects of aged microplastics and their leachates on sludge anaerobic digestion, finding that aged PVC and PET significantly inhibited methane production, with phthalate esters and bisphenol A identified as key inhibitory components.
Unraveling synergistic cascade inhibition of methane production in anaerobic digestion system by polyethylene microplastics and domestic sewage: Physical adsorption, metabolic disruption, and microbial community decoupling
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Researchers systematically explored how the co-presence of polyethylene microplastics and domestic sewage inhibits methane production in anaerobic digestion systems, finding that physical adsorption of microplastics, propionic acid accumulation, and microbial community decoupling identified via multi-omics analysis collectively suppressed cumulative CH4 production by 41.8% compared to controls.
Thermally aged PET microplastics disrupt methanogenic syntrophy via toxic leachates: Microbial assembly dynamics unravel biotoxicity in anaerobic digestion
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Researchers found that thermally aged PET microplastics disrupted methane production during anaerobic digestion more severely than pristine microplastics. The aging process increased reactive oxygen species levels and released toxic chemical compounds that interfered with the microbial communities responsible for biogas production, with longer aging periods causing greater inhibition of methane upgrading.
Revealing the Mechanisms of Polyethylene Microplastics Affecting Anaerobic Digestion of Waste Activated Sludge
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Researchers studied how polyethylene microplastics affect the anaerobic digestion of sewage sludge, a common wastewater treatment process. They found that higher concentrations of microplastics significantly reduced methane production by disrupting microbial communities and enzyme activities essential for digestion. The study reveals that microplastic contamination in wastewater systems can undermine the efficiency of sludge treatment and biogas generation.
Systematic study of microplastics on methane production in anaerobic digestion: Performance and microbial response
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Microplastics are increasingly found in wastewater treatment systems, and this study systematically examined how different types, concentrations, and sizes of microplastics affect the anaerobic digestion process used to break down sewage sludge and generate biogas. Polyethylene microplastics were found to inhibit methane production, with finer particles and higher concentrations causing greater disruption to the microbial communities driving digestion. The findings matter because microplastics in sewage sludge can impair the treatment process and also end up spread on agricultural land when sludge is used as fertilizer.
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