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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.
Microplastics may disturb microbial activity and biofilm development in biological wastewater treatment systems, yet the response of three-dimensional rotating biological contactor start-up biofilms to polypropylene microplastic stress remains unclear. This study evaluated a biofilm initiation strategy using heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria (H-3D-RBCs) and compared it with activated sludge-inoculated systems (A-3D-RBCs) under polypropylene microplastic (PP-MP) exposure. H-3D-RBCs showed superior resistance to PP-MP disturbance, with total nitrogen removal decreasing by only 14 %, compared with an approximately 60 % decline in A-3D-RBCs. Respiratory activity inhibition remained below 15 % in H-3D-RBCs but exceeded 90 % in A-3D-RBCs. 16S rRNA gene sequencing showed that PP-MP reduced species richness and diversity in A-3D-RBCs and was associated with a > 90 % loss of core denitrifying genera, including Corynebacterium and Pseudoxanthomonas, whereas H-3D-RBCs maintained community stability and enriched Pseudoxanthomonas to 13.8 %. Metagenomic analysis indicated that PP-MP impaired nitrification and denitrification potential in A-3D-RBCs, as reflected by decreased genes encoding AMO and HAO, a 51.78 % decrease in nosZ abundance, and enhanced dissimilatory nitrate reduction to ammonium (DNRA), which likely intensified competition with denitrification and promoted nitrogen conversion to ammonia. In contrast, H-3D-RBCs suppressed DNRA and maintained high nosZ abundance. Untargeted metabolomics further showed that PP-MP was associated with metabolic disorders in A-3D-RBCs, especially disruptions in alanine, aspartate, and glutamate metabolism and arginine biosynthesis, whereas H-3D-RBCs preserved these key nitrogen metabolic processes. Overall, this study identifies key vulnerabilities of nitrogen-removal biofilms under PP-MP disturbance and provides multi-omics evidence to support the development of microplastic-resistant biofilm wastewater treatment systems.
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Researchers studied how polyethylene microplastics affect nitrogen removal in wastewater treatment bioreactors and found that low concentrations slightly improved the process, while higher concentrations disrupted it. The microplastics changed the microbial communities responsible for breaking down nitrogen in wastewater. This matters because less effective wastewater treatment means more nitrogen pollution in waterways, and microplastics entering treatment plants could reduce their ability to clean water effectively.
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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.
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