Removal efficiency of micro- and nanoplastics (180 nm-125 μm) during drinking water treatment.

This study investigated the removal efficiency of micro- and nanoplastics (180 nm-125 μm) during drinking water treatment, particularly coagulation/flocculation combined with sedimentation (CFS) and granular filtration under ordinary working conditions at water treatment plants (WTPs). It also studied the interactions between biofilms and microplastics and the consequential impact on treatment efficiency. Generally, CFS was not sufficient to remove micro- and nanoplastics. The sedimentation rate of clean plastics was lower than 2.0% for all different sizes of plastic particles with coagulant Al2(SO4)3. Even with the addition of coagulant aid (PolyDADMAC), the highest removal was only 13.6% for 45-53 μm of particles. In contrast, granular filtration was much more effective at filtering out micro- and nanoplastics, from 86.9% to nearly complete removal (99.9% for particles larger than 100 μm). However, there existed a critical size (10-20 μm) where a significant lower removal (86.9%) was observed. Biofilms were easily formed on microplastics. In addition, biofilm formation significantly increased the removal efficiency of CFS treatment from <2.0% to 16.5%. This work provides new knowledge to better understand the fate and transport of emerging micro- and nanoplastic pollutants during drinking water treatment, which is of increasing concern due to the potential human exposure to micro- and nanoplastics in drinking water.