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The effect of tire microplastics on aerobic granular sludge performance
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Researchers exposed aerobic granular sludge — a wastewater treatment microbe community — to tire-derived microplastics and found that while nutrient removal stayed largely intact, tire particles built up to over half the biomass at high doses and altered the microbial community in ways that increase antibiotic resistance genes. The results show that tire microplastics reaching wastewater plants pose a hidden challenge for sludge management and microbial safety.
Although tire microplastics (TMPs) constitute a substantial portion of microplastic entering wastewater treatment plants, there is a knowledge gap regarding the influence of TMPs on aerobic granular sludge (AGS) systems, which, being more resilient than activated sludge, are becoming increasingly important in modern wastewater treatment. This study investigated the effect of TMPs in wastewater (50, 100, 250, and 500 mg/L) on AGS performance and microbiome. TMPs did not affect organics and phosphorus removal, however, total nitrogen removal was significantly higher (about 9%) at 500 mg TMPs/L compared to the control. TMPs improved biomass settling, but this was due to TMP accumulation (TMPs comprised over 50% of biomass at 500 mg TMP/L) rather than improved granulation. The biomass yield coefficient was five times lower at 500 mg TMP/L than in the control. TMPs elevated dehydrogenase activity (free radical generation) and increased the abundance of microbes involved in polyP synthesis and nitrogen metabolism. TMP presence increased the microbiome potential in terms of antibiotic resistance genes ( cmd and marR ) and the abundance of hydrolases, which degrade rubber-associated ester bonds, and significantly increased the abundance of MP-degraders belonging to genera Ideonella, Rhodobacter , Xanthobacter, and Hydrogenophaga . This study demonstrates that while TMPs in wastewater do not impair nutrient removal by AGS, their accumulation significantly degrades biomass properties, complicating sludge management and disposal. Furthermore, TMPs alter the AGS microbiome's composition and metabolic potential. These findings highlight the importance of integrating AGS systems into urban wastewater treatment, optimizing sludge management strategies, and developing targeted approaches to address the challenges posed by TMPs. • Tire microplastic (TMP) enhanced nitrogen conversions in aerobic granules (AG) • The highest TMP dose caused a 52% TMP buildup in AG and decreased biomass yield • TMP increased dehydrogenase activity and abundance of hydrolases in AG • Increased antibiotic resistance in the microbiome of TMP-exposed AG • TMP increased the abundance of bacteria with plastic degradation potential
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Tire materials disturb transformations of nitrogen compounds and affect the structure of biomass in aerobic granular sludge reactors
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Tire-derived microplastics and their chemical additives were fed into laboratory wastewater treatment reactors, where they reduced nitrogen removal efficiency and physically changed the structure of treatment granules. Importantly, aerobic granular sludge bacteria were able to biodegrade several toxic tire additives including benzothiazole, suggesting that biological treatment systems have some capacity to handle tire pollution — but only if tire material concentrations remain manageable.
Impact of Tire Microplastics on Aerobic Granular Sludge Structure and EPS Composition Under Continuous and Intermittent Aeration
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Researchers added tire microplastics at concentrations of 50–500 mg/L to aerobic granular sludge reactors and found that increasing concentrations reduced granule size under continuous aeration but increased it under intermittent aeration, while total extracellular polymeric substances declined across both conditions.
Impact of Tire-Derived Microplastics on Microbiological Activity of Aerobic Granular Sludge
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This study examined how tire wear particle microplastics — a ubiquitous contaminant in urban stormwater — affect the bacteria responsible for removing nitrogen from wastewater in biological treatment reactors. At increasing tire particle concentrations, bacteria that convert ammonia to nitrate became more active, while bacteria that complete denitrification (converting nitrogen to harmless gas) were significantly suppressed. This imbalance could cause wastewater treatment plants to release more nitrogen into receiving waterways, potentially worsening nutrient pollution and algal blooms. The findings underscore a previously underappreciated way that tire microplastics can impair wastewater treatment infrastructure.
Synergistic analysis of performance, microbial community, and metabolism in aerobic granular sludge under polyacrylonitrile microplastics stress
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Researchers found that low concentrations of polyacrylonitrile microplastics had minimal impact on aerobic granular sludge wastewater treatment, but 100 mg/L severely damaged granule structure and inhibited denitrification and membrane transport gene expression.
Comparative effects of raw and aged tire microplastics on anaerobic fermentation of excess sludge
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Tire microplastics (TMs) that have been aged — as happens when they weather in drainage systems before reaching wastewater treatment plants — are more harmful to the bacterial processes that break down sewage sludge than fresh tire particles. This matters because aged tire microplastics impair the production of volatile fatty acids from sludge treatment, disrupting wastewater facilities and potentially allowing more plastic-contaminated effluent to reach waterways.
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