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Microplastics and nanoplastics in water: Improving removal in wastewater treatment plants with alternative coagulants
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Laboratory tests showed that conventional aluminum sulfate (alum) coagulant becomes much less effective at removing micro- and nanoplastics from water at pH above 7.8—a common condition in municipal wastewater—but switching to aluminum chlorohydrate largely restores removal efficiency. This matters because wastewater treatment plants are a critical barrier preventing microplastics from entering rivers and oceans, and many currently use alum. The study gives water utilities a practical, drop-in solution to significantly improve microplastic capture under challenging water chemistry.
Abstract Coagulation, flocculation, and settling have been shown to be important processes to remove micro‐ and nano‐sized plastic contaminants. However, limited research has been conducted to assess how challenging water chemistry characteristics (including water pH and presence of wastewater colloids) and treatment conditions (such as settling time, coagulant type, flocculant type) impact the removal of these contaminants. Our results show that plastic removal declines at higher pH values using conventional alum as a coagulant. Removal of pristine and aged nanoplastics dropped from 64% and 76%, respectively, at pH 7 to below 20% at pH >7.8. Similarly, polyester microfibre removal decreased from 97% at pH 7 to 85% at pH 8.6. Replacing alum with alternative coagulants resulted in improved plastic contaminant removal at pH >7.8 with an average microfibre removal of 94% (aluminium chlorohydrate) and an average nanoplastic removal of 66% (aluminium chlorohydrate + pDADMAC). Quartz crystal microbalance with dissipation monitoring measurements revealed that aluminium chlorohydrate coagulant species yield a thicker deposition layer on negatively charged surfaces compared to alum. Experiments with alternative flocculants revealed that anionic flocculants result in rapid nanoplastic removal, while cationic flocculants can achieve similar removal given sufficient settling times. Results from our study reveal how coagulant and flocculant selection and environmental conditions, including pH and interactions with wastewater colloids, can affect plastic contaminant removal during primary treatment. Our study also revealed that municipalities can enhance nanoplastic and microfibre removal using alternative aluminium‐based coagulants under challenging pH conditions.
More Papers Like This
Microplastics and nanoplastics in water: Improving removal in wastewater treatment plants with alternative coagulants
AI summary Read the abstract
Conventional water treatment plants that use alum as a coagulant become significantly less effective at removing microplastics and nanoplastics as water pH rises above 7.8, which is common in municipal wastewater. Switching to alternative coagulants — particularly aluminum chlorohydrate and cationic polyamine blends — maintained high removal rates at elevated pH, with nanoplastic removal reaching 71% and microfiber removal staying above 95%. The findings offer practical guidance for upgrading treatment plants to better capture plastic particles before they are discharged into waterways.
Investigating the Potential of Coagulants to Improve Microplastics Removal in Wastewater and Tap Water
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Researchers found that adding coagulants (FeCl3 or Al2(SO4)3) to wastewater and tap water improved microplastic removal, with aluminum sulfate achieving 43% and 62% removal efficiencies respectively, though the high concentrations required suggest that combining coagulants with organic polyelectrolytes could improve practicality.
Microplastics removal from aquatic environment by coagulation: Selecting the best coagulant based on variables determined from a systematic review
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This systematic review and experimental study identifies the most effective methods for removing microplastics from water using coagulation, a common water treatment technique. Researchers tested different coagulants on three types of microplastics and found that aluminum-based coagulants were most effective. These findings could help water treatment plants better remove microplastics from the water supply before it reaches our taps.
The influence of coagulation process conditions on theefficiency of microplastic removal in water treatment
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Researchers investigated how coagulation process conditions — including coagulant type, pH, and microsand addition — affect the removal of polyethylene, PVC, and textile microfibers from river water, municipal wastewater, laundry effluent, and synthetic matrices. Ferric chloride and polyaluminum chloride both achieved substantial removal, with performance varying significantly by water matrix and microplastic type.
Enhancing microplastic removal from natural water using coagulant aids
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Researchers tested different chemical treatments for removing microplastic beads from natural water and found that polyaluminium chloride combined with polyacrylamide achieved over 95% removal across six common plastic types. The treatment worked on particles ranging from 10 to 1,000 micrometers, and natural organic matter in the water actually improved performance. The findings suggest that optimizing standard water treatment processes could be a practical way to reduce microplastic contamination in drinking water sources.
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