Conventional and biological treatment for the removal of microplastics from drinking water

This study examines the removal of microplastics and other anthropogenic particles (>10 mu m) from surface water by a full-scale conventional drinking water treatment plant. The treatment process is composed of coagulation with aluminum hydroxide, flocculation, anthracite-sand filtration, and chlorination. Samples were also collected from pilot-scale biological filters consisting of anthracite-sand or granular activated carbon (GAC) media operated with or without pre-ozonation and at a range of different empty-bed contact times (EBCTs). Particles in 10 L water samples collected in duplicate using a fully enclosed sampling apparatus were separated using sieves with 500 mu m, 300 mu m, 125 mu m, and 45 mu m openings followed by filtration through 10 mu m polycarbonate filters. Particles were counted using stereomicroscopy and characterized using mu-Raman spectroscopy. Full-scale conventional treatment removed 52 % of anthropogenic particles when comparing raw (42 +/- 18 particles/L) and finished water (20 +/- 8 particles/L). Coagulation, flocculation, and sedimentation accounted for the highest removal (70 %) of any individual unit process. Overall removal was reduced to 52 %, the difference being attributed to airborne particle deposition that occurred while water was detained in a clearwell (exposed to atmosphere via ventilation) that was used to achieve the required contact time for disinfection. The majority of the particles (>80 %) were identified as fibers 10-45 mu m; microplastics were predominantly composed of polyester while the non-plastic anthropogenic particles were primarily cellulose. None of the pilot filter configurations examined resulted in significantly fewer microplastics when compared to full-scale conventional filtration. This study illustrates that the removal efficiency of conventional treatment may be limited when considering microfibers <45 mu m in size.

Automated summary

This study evaluates the removal of microplastics and other anthropogenic particles from surface water by a full-scale conventional drinking water treatment plant. The highest removal efficiency was observed in the coagulation, flocculation, and sedimentation processes. However, the overall removal efficiency may be limited by airborne particle deposition during water detention.