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Extracellular polymers mediated stress response mechanisms: Functional responses of aerobic granular sludge under combined microplastic/nanoplastic and copper ion stress
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Wastewater treatment plants use clumps of bacteria (called "granular sludge") to filter out pollutants like ammonia and heavy metals, but this study found that tiny plastic particles, especially nanoplastics, combined with copper can weaken these bacterial clumps and reduce their ability to remove nitrogen pollution. This matters because as microplastics and nanoplastics become more common in our water systems, they could make it harder for treatment plants to fully clean wastewater, potentially allowing more pollutants to end up in rivers, drinking water sources, and ultimately our bodies.
The coexistence of micro- and nanoplastics with heavy metals may affect the structure and treatment performance of aerobic granular sludge (AGS). This study compared the operational performance, extracellular polymeric substances (EPS) characteristics, and transcriptional responses of AGS under combined stress from polystyrene microplastics (Ps-MPs) and nanoplastics (Ps-NPs) with Cu. The chemical oxygen demand (COD) removal rates in all reactors remained above 90%. By the end of Stage II, the ammonia nitrogen removal rates in the Ps-MPs + Cu and Ps-NPs + Cu groups had decreased to 78.95% and 75.46%, respectively; the former achieved an average total nitrogen removal rate of 72.14% through enhanced denitrification, while the latter significantly inhibited denitrification at high concentrations. The binding constant between Ps-NPs and EPS was 4.57 × 10 L/mol, enabling this system to achieve the highest Cu removal efficiency (79.27%). The EPS contents at the end of the Ps-MPs + Cu and Ps-NPs + Cu groups were 159.97 and 145.31 mg/g VSS, respectively, and the PN/PS ratios decreased to 2.43 and 1.49, respectively. Ps-MPs + Cu can mitigate the adverse effects of Cu on AGS aggregation, whereas Ps-NPs + Cu weakens particle stability. Transcriptomic analysis further elucidated the stress response mechanisms at the molecular level, confirming that AGS compensates for impaired biochemical pathways by synergistically upregulating genes related to nitrogen metabolism and regulates the expression of EPS synthesis genes to enhance the physical barrier function of the biofilm. This study elucidates the differences in EPS responses mediated by microplastic particle size, providing a theoretical basis for enhancing the resilience of the AGS process to combined pollution from different contaminants.
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Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances
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Researchers found that both micro- and nanoplastics at realistic concentrations harmed the performance of aerobic granular sludge, a technology used for wastewater treatment, by reducing its ability to remove nitrogen. The plastic particles interacted with the sticky substances that hold the sludge granules together, weakening their structural integrity. The study reveals a specific mechanism by which plastic pollution can undermine wastewater treatment systems that communities rely on for clean water.
Impaired denitrification of aerobic granules in response to micro/nanoplastic stress: Insights from interspecies interactions and electron transfer processes
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This study found that micro- and nanoplastics in wastewater disrupt the ability of beneficial bacteria to remove nitrogen through a process called denitrification. After 90 days of plastic exposure, the communication system bacteria use to coordinate their activity broke down, leading to an imbalance where some bacteria stopped contributing while still consuming shared resources. This reduced the overall efficiency of biological wastewater treatment, a system many communities rely on to clean their water.
Effects of polyvinylchloride microplastics on the toxicity of nanoparticles and antibiotics to aerobic granular sludge: Nitrogen removal, microbial community and resistance genes
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Researchers examined how PVC microplastics affect wastewater treatment systems that also contain copper oxide nanoparticles and the antibiotic ciprofloxacin. They found that low concentrations of microplastics actually reduced some toxic effects of the other pollutants, but higher concentrations worsened nitrogen removal efficiency and increased antibiotic resistance genes. The study highlights the complex ways microplastics can alter the behavior of other contaminants in water treatment.
Mechanistic insights into superior biofilm formation with heterotrophic nitrification-aerobic denitrification bacteria under polypropylene microplastic stress
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Microplastics are known to mess with the helpful bacteria that treat wastewater and remove nitrogen pollution, but this study found that using a special type of bacteria to "seed" water treatment systems made them much more resistant to this disruption. This matters because as plastic pollution keeps growing, protecting the microbial communities that clean our water is essential for keeping waterways—and the water we eventually drink—free of excess nitrogen pollution.
Micro- and nanoplastics in granular sludge systems: mechanisms of disruption, retention, and microbial adaptation in wastewater treatment technologies
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This review examines how micro- and nanoplastics disrupt the biological systems used to treat wastewater, focusing on granular sludge technologies. Plastic particles damage the microbial communities that break down waste by causing oxidative stress and breaking apart the protective structures that hold bacteria together. This matters because if wastewater treatment becomes less effective due to plastic contamination, more pollutants including microplastics could pass through into waterways that supply drinking water.
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