Citation: Kwon, H.J.; Hidayaturrahman, H.; Peera, S.G.; Lee, T.G. Elimination of Microplastics at Different Stages in Wastewater Treatment Plants. Water 2022, 14, 2404. https://doi.org/10.3390/ w14152404 Academic Editors: Jiangchi Fei, Qian Zhou, Zhenxing Wang and Lizhi Xiong Received: 21 June 2022 Accepted: 29 July 2022 Published: 3 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Elimination of Microplastics at Different Stages in Wastewater Treatment Plants Hyuk Jun Kwon 1 , Haerul Hidayaturrahman 1,2 , Shaik Gouse Peera 1, * and Tae Gwan Lee 1, * 1 Department of Environmental Science, Keimyung University, Daegu 42601, Republic of Korea; kanata86@nate.com (H.J.K.); haerul.hidayat@gmail.com (H.H.) 2 National Research and Innovation Agency, Central Jakarta 10340, Indonesia * Correspondence: gouse@kmu.ac.kr (S.G.P.); wateree@kmu.ac.kr (T.G.L.) Abstract: Microplastic pollution has been widely studied as a global issue due to increased plastic usage and its effect on human and aquatic life. Microplastics originate from domestic and industrial activities. Wastewater treatment plants (WWTPs) play an important role in removing a significant amount of microplastics; otherwise, they end up in bioaccumulation. This study provides knowledge about the characteristics of microplastics, removal efficiency, and the correlation between wastewater quality and microplastic concentrations from three different WWTPs that differ in the type of bio- logical and advanced wastewater treatment techniques that are believed to play an important role in microplastic removal. Microplastics of different types, such as fragments, fibers, and beads, are identified by using an optical microscope before and after the treatment process at each stage to assess the effect of different treatment techniques. In the screening unit and primary clarifier unit, WWTP-B shows the highest removal efficiency with 74.76% due to a distribution flow system installed before the primary clarifier to ensure a constant flow of wastewater. WWTP-B uses a bioreactor consisting of a filter plate coated with activated carbon (BSTS II) that can enhance the adaptability and adhesion of microorganisms and showed that 91.04% of the microplastic was removed. Furthermore, only WWTP-A and WWTP-B were applied coagulation, followed by the disc filter; they showed significant results in microplastic removal, compared to WWTP-C, which only used a disc filter. In conclusion, from all WWTP, WWTP-B shows good treatment series for removing microplastic in wastewater; however, WWTP-B showed a high rate of microplastic removal; unfortunately, large amounts of microplastics are still released into rivers. Keywords: wastewater; microplastics; removal; treatment plant; coagulation; disc filter 1. Introduction Plastics are widely used in various sectors of life, especially as packaging materials. Plastic has many advantages ranging from being cheap, durable, lightweight, and easy to obtain; however, after being used, all plastics end up as waste that accumulates in nature, especially in the aquatic environment [1]. The presence of plastic in water bodies is one of */the main factors affecting water pollution because it is difficult to control. In general, plastic waste is classified depending on size, such as megaplastics (more than 500 mm), macroplastics (50–500 mm), mesoplastics (5–50 mm), microplastics (<5 mm), and nanoplastics (less than 0.3 mm) [2,3]. Microplastics can be grouped into primary and secondary microplastics [4,5]. Primary microplastics are intentionally produced in micro sizes for skincare products, textile fibers, and other industrial uses. Secondary microplastics are generated from the degradation or breakdown process of large plastic particles [6,7]. Microplastics derived from various point sources and non-point sources are eventually carried by rivers into water bodies, including lakes, seas, and oceans [5,8]. In the last few years, the accumulation of microplastics in marine ecosystems has gradually increased, and microplastics found in aquatic environments have long-lasting detrimental effects on Water 2022, 14, 2404. https://doi.org/10.3390/w14152404 https://www.mdpi.com/journal/water