The Removal of Microplastics by Wastewater Treatment Plants in Charleston, SC and a Survey of Treatment Processes
Wastewater treatment plants (WWTPs) serve to collect and treat wastes that are known to include microplastic (MP) particles, fibers and microbeads. WWTPs are often suspected as a source of MPs into the marine environment, yet few studies have confirmed these suspicions. The present study aimed to answer two questions regarding the fate of MPs in WWTPS: i) what is the MP loading and removal efficiency (RE) of 3 WWTPs discharging treated effluent into the Charleston Harbor over the course of a year; and ii) what is the capacity of WWTPs in SC to remove MPs during treatment? We found that MP concentrations per L influent influent varied within a factor of 2.5 at each WWTP, and the MP concentrations per L effluent varied within a factor of 4.8 and 4.2 at RR and CS, respectively, and within a factor of 2.7 at PI. PI had the highest average RE of 97.6%, likely due to the use of primary clarifiers. RR and CS had average RE’s of 85.2% and 85.5%, which were consistent with other published studies that have found RE’s to improve with primary clarification and specific tertiary unit processes. Of the plants surveyed in SC, plants with primary clairifiers accounted for 22% of WWTPs and plants with sand or membrane filtration accounted for 31%. Retrofitting existing plants with primary clarifiers, sand filtration, or membrane filtration would likely increase RE’s in WWTPs in SC, but updates are dependent on costs and site specific factors.