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Mechanisms of Natural Organic Matter Influencing on Coagulation Process for Nanoplastics Removal from Water
Summary
Scientists found a water treatment method that removes over 94% of nanoplastics (tiny plastic particles too small to see) from water using common purification chemicals. However, they discovered that natural substances already in water, like decaying plant matter and proteins from organic material, can significantly weaken this cleanup process, with one protein-based substance cutting removal effectiveness by nearly 30%. This matters because it shows that real-world water treatment plants may need to account for these natural substances to reliably filter out nanoplastics before they reach our drinking water.
Nanoplastics pose potential risks to drinking-water safety. In this study, 50 nm polystyrene nanoplastics (PSNPs) were selected as the target pollutant, and polyaluminum chloride (PAC) combined with anionic polyacrylamide (PAM) was used for coagulation. The process parameters were optimized using response surface methodology, and the optimal conditions were a PAC dosage of 5.5 mg/L, a PAM dosage of 1.4 mg/L, and pH 7.5, under which the PSNPs removal efficiency reached 94.2%. Under these optimized conditions, the inhibitory effects and mechanisms of three representative natural organic matter (NOM) components—humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA)—were systematically investigated. All three NOM components inhibited PSNPs removal in a concentration-dependent manner. Combined FTIR, XPS, and 2D-COS analyses showed that HA (0.5–2.0 mg/L) reduced PSNP removal by up to 16.45 percentage points mainly through π–π interactions and hydrogen bonding, resulting in binding-site masking. BSA (5–15 mg/L) caused the strongest inhibition, reducing PSNP removal by up to 28.06 percentage points, probably through hydrophobic adsorption and formation of a protein layer that induced steric hindrance. SA (0.2–0.8 mg/L) caused moderate inhibition, decreasing PSNPs removal by 1.5–11.9 percentage points by introducing additional negative charges through carboxyl groups and enhancing electrostatic stabilization. These results indicate that different NOM components interfere with PSNPs coagulation through distinct pathways, including binding-site masking, physical blocking, electrostatic stabilization, and potential competition for coagulants.