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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.
Tire materials (TMs) present a notable hazard due to their potential to release harmful chemicals and microplastics into the environment. They can infiltrate wastewater treatment plants, where their effects remain inadequately understood, raising concerns regarding their influence on treatment procedures. Thus, this study investigated the impact of TMs in wastewater (10, 25, 50 mg/L) on wastewater treatment efficiency, biomass morphology, and microbial composition in aerobic granular sludge (AGS) reactors. TM dosage negatively correlated with nitrification and denitrification efficiencies, reducing overall nitrogen removal, but did not affect the efficiency of chemical-oxygen-demand removal. The presence of TMs increased the diameter of the granules due to TM incorporation into the biomass. The most frequently leached additives from TMs were N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine, benzothiazole (BTH), and 2-hydroxybenzothiazole. In the treated wastewater, only BTH and aniline were detected in higher concentrations, which indicates that tire additives were biodegraded by AGS. The microbial community within the AGS adapted to TMs and their chemicals, highlighting the potential for efficient degradation of tire additives by bacteria belonging to the genera Rubrivivax, Ferruginibacter, and Xanthomonas. Additionally, our research underscores AGS's ability to incorporate TMs into biomass and effectively biodegrade tire additives, offering a promising solution for addressing environmental concerns related to TMs.
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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.
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.
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.
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.
Ecotoxicology of micronized tire rubber: Past, present and future considerations
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This review synthesizes what is known about the ecotoxicology of micronized tire rubber particles, which are increasingly identified as a significant fraction of environmental microplastics, examining their effects on aquatic and terrestrial organisms. The authors note that tire rubber contains a complex mixture of chemical additives that may drive toxicity beyond the physical effects of the particles themselves.
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