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Microplastic stress reshapes nitrogen removal, microbial networks and metabolism mechanisms in vertical flow constructed wetlands
Summary
Scientists found that tiny plastic particles (microplastics like polystyrene and PVC) can seriously mess up the natural water treatment systems—called constructed wetlands—that are supposed to filter out harmful nitrogen waste from wastewater. In lab tests, these microplastics disrupted the helpful bacteria that break down nitrogen pollution, cutting the wetlands' cleaning efficiency by roughly half or more. This matters because if microplastics are weakening these treatment systems in the real world, wastewater could end up releasing more nitrogen pollution into rivers and lakes, potentially harming water qu
Vertical flow constructed wetlands (VFCWs) are widely recommended for onsite wastewater treatment. Limited research is available on how microplastics (MPs), particularly polystyrene (PS) and polyvinyl chloride (PVC), alter biological nitrogen transformation in VFCWs. This study investigates the influence of MPs (PS and PVC) on the nitrification-denitrification, microbial community structure and metabolic functioning in VFCWs, operated under two phases, i.e., Phase-I (control) and Phase-II (with MPs), for 180 days, and changes in removal efficiency (ammonium-N (NH 4 + -N); nitrite (NO 2 -N); nitrate-N (NO 3 -N); total nitrogen (TN)) and microbial community structure were recorded. Results suggested that MPs affect the nitrogen removal performance of VFCWs, with a decrease in NH 4 + -N, NO 3 -N, and TN removal efficiencies by 63.87 – 70.38%, 47.90 – 64.04%, and 39.3 – 55.33%, respectively, compared to Phase-I. MPs inhibited the abundance of nitrifiers ( Nitrospira and Tepidiforma ) and suppressed key functional genes ( amoA , hao and nxrA ) while enriching dissimilatory nitrate reduction to ammonium (DNRA)-associated keystone taxa (e.g., Anaeromyxobacter, Tepidisphaera, Pseudomonas ) and denitrification markers ( nirK, nirS, nosZ ). Overall, VFCW-I (PS) demonstrated better functional resilience than VFCW-II (PVC), but both showed disrupted microbial equilibrium and reduced nitrogen removal. However, our conclusions were derived from lab-scale CWs; we expect these findings to offer valuable insights for developing an effective policy framework to manage and mitigate the MPs pollution in real-world wetlands.