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Biodegradable microplastics influence on organic component microbial transformation during sludge composting
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Scientists found that composting sewage sludge at very hot temperatures (70°C) breaks down "biodegradable" plastic particles (made from PLA, a common compostable plastic) much more effectively than at lower temperatures, thanks to heat-loving microbes that thrive under these conditions. This matters because sludge from wastewater treatment is often turned into fertilizer, so finding ways to actually break down microplastics before they end up on farmland—and potentially in our food and water—could reduce a route by which these particles reach our bodies.
Sludge-based composting offers a promising pathway for sustainable resource recovery and pollution mitigation; however, the biodegradation mechanisms of biodegradable microplastics (MPs) during this process and their interactions with organic matter transformation have not yet been investigated. This study investigated the biodegradation response of polylactic acid (PLA) and the coupled dynamics of microbial communities and organic matter transformation during a 33-day sludge composting process at 55 °C and 70 °C. Scanning electron microscopy (SEM) revealed that thermophilic composting (70 °C) induced severe structural degradation of PLA-MPs, characterized by extensive void formation, surface wrinkling, and fragmentation. Compared to the mesophilic control, thermophilic composting significantly enhanced the transformation and turnover of key organic components, including amino acids (AAs), reducing sugars (RSs), polysaccharides, and polyphenols (PPs). Bacterial communities were predominantly composed of thermophilic Firmicutes (74.6-98.2%), with significant contributions from Actinobacteria, Chloroflexi, and Bacteroidetes, while fungal communities were dominated by Ascomycota and Basidiomycota. Although the addition of MPs reduced overall microbial richness and diversity, high-temperature conditions selectively enriched key organic matter-degrading taxa, suggesting a functional trade-off where thermal pressure favors specialized degradative capacity over generic community complexity. Co-occurrence network analysis revealed that high-temperature composting combined enhanced microbial functional connectivity and metabolic redundancy for both MPs and organic component transformation, promoting the proliferation of polysaccharides and lignocellulose-decomposing bacteria and fungi. These findings provide mechanistic insights into biodegradable MP degradation during thermophilic composting and establish a theoretical foundation for designing efficient MP remediation strategies in sludge treatment systems. Future studies are warranted to evaluate these findings under field-scale composting conditions and explore the integration of microbial inoculants to optimize the removal efficiency of biodegradable MPs.
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Enhanced in situ biodegradation of microplastics in sewage sludge using hyperthermophilic composting technology
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Hyperthermophilic composting technology (operating above 70°C) was tested for its ability to biodegrade microplastics in sewage sludge in situ, with results showing significant reduction in microplastic abundance compared to conventional composting. This enhanced treatment approach could reduce the microplastic load delivered to agricultural soils when biosolids are land-applied.
Early thermal pulses drive interfacial pre-aging and plastisphere pre-shaping: An overlooked pre-conditioning pathway in PLA microplastic aging during composting
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"Compostable" plastics like PLA don't always fully break down—they can leave behind tiny microplastic fragments that end up in soil used for farming. This study found that a short burst of extra-high heat early in the composting process makes these plastic bits break down faster and more completely by the end, without taking any extra time. That's good news, since it suggests a simple tweak to composting methods could help reduce the amount of lingering microplastic contamination in the food we grow and eat.
Effects of Inoculum Source and Incubation Temperature on Bacterial Community Structure and Predicted Functional Potential Associated with Polylactic Acid (PLA) Degradation
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Scientists found that different compost microbe sources and temperatures change which bacteria break down PLA, a common "biodegradable" plastic used in food packaging and utensils. Hotter compost conditions worked better and favored different bacteria than room-temperature setups. This matters because it helps identify which microbes and conditions actually break down these plastics, informing better composting practices and reducing plastic waste that could otherwise persist in the environment.
Microplastics in sewage sludge destined to anaerobic digestion: The potential role of thermal pretreatment
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Researchers found that thermal pretreatment of sewage sludge at 120°C did not degrade conventional PET microplastics but did alter biodegradable microplastics, which also boosted methane production during anaerobic digestion, raising concerns about how different microplastic types behave in sludge treatment.
Occurrence, analysis of microplastics in sewage sludge and their fate during composting: A literature review
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This literature review synthesizes data on microplastic concentrations in sewage sludge from wastewater treatment plants across 18 countries, finding concentrations ranging from 7,910 to 495,000,000 particles per kilogram dry weight. The review discusses fate during composting and recommends inoculation with plastic-degrading microbes and high-temperature composting as promising remediation approaches.
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