Microplastics and Wastewater Treatment Plants—A Review

Abstract

The emission of microplastics into nature poses a threat to aquatic and terrestrial ecosystems. Their penetration of the food chain presents a danger to human health as well. Wastewater treatment plants can be seen as the last barrier between microplastics and the environment. This review focuses on the impact of waste treatment plants in retaining microplastics. Studies show that no wastewater treatment method leads to a complete retention of microplastics, and so wastewater treatment plants themselves are viewed as point sources for the discharge of microplastics into the aquatic environment. Problems associated with the utilization of microplastic loaded sewage sludge are also discussed in the review. Journal of Water Resource and Protection found as micropellets in cosmetic formulations and in facial cleaners and body scrubs (median size of 0.2 -0.4 mm), as microspherules in toothpastes (2 -5 μm in size), as well as in scrubbers used for air-blasting surfaces to remove paints and rust [25] and as drilling fluids in oil and gas exploration. A newer application is their use in drug delivery systems [26] [27]. In addition, synthetic polymer containing microparticles can also be released by the degradation of materials. The release of microfibers as a result of the washing of textiles has been widely reported as a source of microplastics [28] [29] [30] [31] [32]. These synthetic fibers, released by washing machines, are transported to waste water treatment plants [29] [33], where a considerable amount of them pass through the different treatment stages into the effluents due to their smaller size and enter the aquatic environment. It is estimated that around 35% of microplastics reaching the ocean are from synthetic textiles [34].Inventories of microplastics entering the environment have been attempted by organizations in different countries. A breakdown of the sources of microplastics in Sweden has been provided by Magnusson [35], which is given in detail below as an example of typical microplastic streams in developed countries. There is microplastic emission from plastic production, sandblasting material, cosmetic products, pharmaceutical drugs, textiles, road material and coatings. Using a spill factor of 0.04%, which was also used by Sundt et al. [26] for the estimation of pellet loss from the Norwegian plastic production plants, K. Magnusson et al. [35] have calculated a direct micropellet emission of 298 tons per year. In addition to that, there is loss due to the handling of plastic pellets which is set at between 0.0005% and 0.01%, adding another 12 -235 tons of microplastics emitted into the environment. These numbers were modeled on emission factors proposed by Lassen et al. [36] for the Danish production industry. However, no actual measured numbers of emissions of microplastics during production exist.The use of microplastics (e.g. of urea formaldehyde resins) in abrasive products for sandblasting has been deemed to be limited, and the use of these materials in Swedish shipyards is strictly regulated...

Towards control strategies for microplastics in urban water

“…Wastewater, stormwater and CSOs seem to be important pathways to receiving surface waters (Bollmann et al 2019 ). In addition to surface water, microplastics are found in large quantities in sewage sludge (Habib et al 2020 ) and in stormwater sediments (Borg Olesen et al 2019 ). The properties of different microplastics can influence the retention at the WWTP.…”

Microplastics in Wastewater

“…Microfibers in the effluent of WWTPs either discharged to aquatic or terrestrial environments are mistakenly ingested by organisms causing adverse impacts due to their microscopic sizes and length-to-diameter ratio (Dris et al 2018). Close relationship is identified between fibers collected from shore sediment and samples collected from WWTP effluent, showing a significant amount of detected microfibers is closely associated with effluent discharge (Habib et al 2020).…”

“…The fate and pathways of MPs in WWTPs are from raw sewage to treated effluent, settled sludge, or concentrated wash water. Recently, several researchers have assessed occurrence of MPs in sludge treatment processes in WWTPs (Habib et al 2020). Table 3 summarizes the MP abundance in different types of sludge from ten recent studies.…”

“…MPs eventually reach the oceans via effluent discharge, beach littering, road runoff, and illegal dumping activities. WWTPs, which have been identified as one of the largest sources of MPs in the water environments, have recently gotten attention from academic and governmental agencies (Habib et al 2020). Thus, not only can significantly more MPs be found in treated effluent, but also elevated amounts of MPs have been found in the sediments collected at study sites near the outflow of WWTPs (Browne et al 2011).…”

“…The development of standard protocols and agreement on unit expression are urgent so that scholars can facilitate the research on MP pollution and their understanding in the actual fate of MPs in WWTPs and infer conclusions (Renner et al 2018). It is important to conduct research on MP removal mechanisms in the treatment methods, MP effects on biological treatment and further advancement in the existing WWTP design for enhancing MP removal (Conley et al 2019;Habib et al 2020).…”