Wastewater Treatment Works (WwTW) as a Source of Microplastics in the Aquatic Environment

TLDR

Municipal effluent from wastewater treatment works is suspected to be a major source of microplastics in the environment because many personal‑care products contain plastic microbeads. The study aims to detail the fate of microplastics during treatment and to determine at which stage removal occurs. Researchers sampled a secondary plant (population equivalent 650 000) at multiple treatment stages to assess microplastic removal. They found that the plant reduced microplastics from an average of 15.70 MP L⁻¹ to 0.25 MP L⁻¹ (98.4 % removal), yet still releases about 65 million microplastics per day, with most removal occurring in the grease‑removal stage where microbeads were detected.

Abstract

Municipal effluent discharged from wastewater treatment works (WwTW) is suspected to be a significant contributor of microplastics (MP) to the environment as many personal care products contain plastic microbeads. A secondary WwTW (population equivalent 650 000) was sampled for microplastics at different stages of the treatment process to ascertain at what stage in the treatment process the MP are being removed. The influent contained on average 15.70 (±5.23) MP·L–1. This was reduced to 0.25 (±0.04) MP·L–1 in the final effluent, a decrease of 98.41%. Despite this large reduction we calculate that this WwTW is releasing 65 million microplastics into the receiving water every day. A significant proportion of the microplastic accumulated in and was removed during the grease removal stage (19.67 (±4.51) MP/2.5 g), it was only in the grease that the much publicised microbeads were found. This study shows that despite the efficient removal rates of MP achieved by this modern treatment plant when dealing with such a large volume of effluent even a modest amount of microplastics being released per liter of effluent could result in significant amounts of microplastics entering the environment. This is the first study to describe in detail the fate of microplastics during the wastewater treatment process.