Microplastics in wastewater treatment plants and their contributions to surface water and farmland pollution in China

Shu-Yan Ren; Qing Sun; Shi-Yong Xia; De Tong; Hong-Gang Ni

doi:10.1016/j.chemosphere.2023.140239

Microplastics in wastewater treatment plants and their contributions to surface water and farmland pollution in China

Chemosphere. 2023 Dec:343:140239. doi: 10.1016/j.chemosphere.2023.140239. Epub 2023 Sep 19.

Authors

Shu-Yan Ren¹, Qing Sun², Shi-Yong Xia³, De Tong⁴, Hong-Gang Ni⁵

Affiliations

¹ School of Urban Planning and Design, Peking University Shenzhen Graduate School, Shenzhen, 518055, China. Electronic address: 2206394203@pku.edu.cn.
² School of Urban Planning and Design, Peking University Shenzhen Graduate School, Shenzhen, 518055, China. Electronic address: 2001112114@pku.edu.cn.
³ Laboratory of Atmospheric Observation Supersite, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen, 518055, China. Electronic address: 1901111947@pku.edu.cn.
⁴ School of Urban Planning and Design, Peking University Shenzhen Graduate School, Shenzhen, 518055, China. Electronic address: tongde@pkusz.edu.cn.
⁵ School of Urban Planning and Design, Peking University Shenzhen Graduate School, Shenzhen, 518055, China. Electronic address: nihg@pkusz.edu.cn.

PMID: 37734500
DOI: 10.1016/j.chemosphere.2023.140239

Abstract

Wastewater treatment plants (WWTPs) are usually considered gateways for microplastics (MPs) to enter the environment because large amounts of sewage are produced and MPs are incompletely removed during treatment processes. However, the contribution of effluent MPs to aquatic environmental pollution and that of sludge application to MPs in agricultural soil are still unknown. This study examines the presence of MPs in sewage and sludge in Shenzhen WWTPs and estimates the annual mass loading of MPs from WWTPs to surface water and farmland soil in China. According to our results, for Shenzhen, the annual contribution of MPs from WWTPs (which was obtained by multiplying the annual treated sewage volume by the estimated MP density in the treated sewage) to surface water could be 70.6-302 tons. With a normalized extrapolation model of population density, the contribution of national urban WWTPs to MPs in surface water was estimated to be 734 -3.10 × 10³ tons/year, of which 220-950 tons/year entered the marine environment. Furthermore, the riverine flux of MPs from WWTPs to the ocean amounts to at least 7.0%-30% based on the maximum value of WWTP contribution to MPs in surface water. For sludge, the potential contribution of MPs to agricultural soil from Shenzhen WWTPs is (1.00-2.80) × 10³ tons/year. With the above calculation procedure, it was estimated that the contribution of MPs to farmland from sludge application in China is (1.30-3.90) × 10⁴ tons/year. The source appointment results for MPs in China's agricultural soil suggested that the contributions of the main four sources, namely, atmospheric deposition, agricultural mulch film, sludge application, and organic fertilizers, are 52%, 30%, 11%, and 7.0%, respectively.

Keywords: Agricultural soil; Microplastics; Sludge application; Surface water; Wastewater treatment plant.