To what extent are wastewater treatment systems a gateway for microplastic particles in the aquatic and terrestrial environments?

Abstract

Sewage treatment plants are designed to handle wastes that include several types of pollutants, including microplastics (MPs), which are synthetic polymer materials fragmented to sizes < 5 mm. Investigating the abundance and removal efficiency rates of MPs in wastewater treatment plants is important because the water body to which plant effluents are discharged may be adversely affected by the released MPs. Therefore, the abundance, characteristics, and removal of MPs at two sewage treatment plants located on the southwest coast of Norway are studied. Twenty-four samples were collected across two sampling sessions by using an ad hoc-designed plastic-free water sampling device, which was improved by applying a cascade of certified stainless-steel sieves. A combined sequence of enzymatic and strong oxidative incubations was performed for sample preparation. The obtained samples were chemically characterized and quantified using thermoanalytical techniques. The overall amounts of polymers in the inlet wastewater and outlet water were 366-616 μg/L and 34-57 μg/L, respectively, indicating an approximate MPs removal efficiency of 78%-85%. Polyethylene (≈ 36%-68%), polypropylene (≈ 7%-48%), polystyrene (≈ 5%-6%), polyvinyl chloride (≈ 15%-26%), polyamide (≈ 2%), polymethacrylate (≈ 3%-4%), polycarbonate (≈ 2%), and polyethylene terephthalate (≈ 9%-32%) were detected in the investigated samples. In biosolids, the overall quantity of MPs was 3.8-5.5 mg/g dry weight across the two investigated sewage treatment plants. Polyethylene (≈ 24%-44%), followed by polyvinyl chloride (PVC) (≈ 11%-16%), and polyamide (≈ 2%-22%) were the most commonly recurring polymer types. The outcomes of this study indicate that MPs are removed efficiently from wastewaters. However, large amounts of MPs accumulate in biosolids. Therefore, sludge dumping management procedures need to be improved to lower the amount of MPs released into the environment through effluents and biosolids.

Keywords

Microplastics / sewage treatment plants / pyrolysis / sewage sludge

References

[1] Sheavly SB.Marine debris & plastics: environmental concerns, sources, impacts and solutions.J Polym Environ2007;15:301-5

[2] Duis K.Microplastics in the aquatic and terrestrial environment: sources (with a specific focus on personal care products), fate and effects.Environ Sci Eur2016;28:2 PMCID:PMC5044952

[3] Tian W,Zhang H.Microplastic materials in the environment: problem and strategical solutions.Prog Mater Sci2023;132:101035

[4] van Wezel A, Caris I, Kools SA. Release of primary microplastics from consumer products to wastewater in the Netherlands.Environ Toxicol Chem2016;35:1627-31

[5] Mintenig SM,Löder MGJ,Gerdts G.Identification of microplastic in effluents of waste water treatment plants using focal plane array-based micro-Fourier-transform infrared imaging.Water Res2017;108:365-72

[6] Eerkes-Medrano D,Aldridge DC.Microplastics in freshwater systems: a review of the emerging threats, identification of knowledge gaps and prioritisation of research needs.Water Res2015;75:63-82

[7] Simon M,Vollertsen J.Quantification of microplastic mass and removal rates at wastewater treatment plants applying Focal Plane Array (FPA)-based Fourier Transform Infrared (FT-IR) imaging.Water Res2018;142:1-9

[8] Gomiero A,Agustsson T,van Thiel T.First record of characterization, concentration and distribution of microplastics in coastal sediments of an urban fjord in south west Norway using a thermal degradation method.Chemosphere2019;227:705-14

[9] Hermabessiere L,Boricaud B.Optimization, performance, and application of a pyrolysis-GC/MS method for the identification of microplastics.Anal Bioanal Chem2018;410:6663-76

[10] Magni S,Pittura L.The fate of microplastics in an Italian Wastewater Treatment Plant.Sci Total Environ2019;652:602-10

[11] Liu K,Wei N,Li D.Accurate quantification and transport estimation of suspended atmospheric microplastics in megacities: implications for human health.Environ Int2019;132:105127

[12] Gomiero A,Øysæd KB.First occurrence and composition assessment of microplastics in native mussels collected from coastal and offshore areas of the northern and central Adriatic Sea.Environ Sci Pollut Res Int2019;26:24407-16

[13] Carr SA,Tesoro AG.Transport and fate of microplastic particles in wastewater treatment plants.Water Res2016;91:174-82

[14] Leslie HA,van Velzen MJ.Microplastics en route: field measurements in the Dutch river delta and Amsterdam canals, wastewater treatment plants, North Sea sediments and biota.Environ Int2017;101:133-42

[15] Fojt J,Přikryl R,Kučerík J.A critical review of the overlooked challenge of determining micro-bioplastics in soil.Sci Total Environ2020;745:140975

[16] Ivleva NP.Chemical analysis of microplastics and nanoplastics: challenges, advanced methods, and perspectives.Chem Rev2021;121:11886-936

[17] Picó Y.Pyrolysis gas chromatography-mass spectrometry in environmental analysis: focus on organic matter and microplastics.TrAC Trend Anal Chem2020;130:115964

[18] Sun J,Wang Q,Ni BJ.Microplastics in wastewater treatment plants: detection, occurrence and removal.Water Res2019;152:21-37

[19] Ziajahromi S,Rintoul L.Wastewater treatment plants as a pathway for microplastics: development of a new approach to sample wastewater-based microplastics.Water Res2017;112:93-9

[20] Andrady AL.Applications and societal benefits of plastics.Philos Trans R Soc Lond B Biol Sci2009;364:1977-84 PMCID:PMC2873019

[21] Horodytska O,Fullana A.Plastic waste management: current status and weaknesses. In: Plastics in the aquatic environment - Part I: Current status and challenges. Cham: Springer International Publishing; 2019. pp. 289-306.

[22] Microplastics; occurrence, levels and implications for environment and human health related to food. Opinion of the Scientific Steering Committee of the Norwegian Scientific Committee for Food and Environment. 2019. Available from: https://vkm.no/download/18.5b7a016e16dcd89a3977dc60/1571650615867/Microplastics;%20occurrence,%20levels%20and%20implications%20for%20environment%20and%20human%20health%20related%20to%20food.pdf. [Last accessed on 25 Apr 2024]

[23] Simonsen M,Saetra Ø.Coastal transport of river-discharged radionuclides: impact of speciation and transformation processes in numerical model simulations.Sci Total Environ2019;669:856-71

[24] Ibrekk HO,Faafeng B.Nutrient loading to norwegian coastal waters and its contribution to the pollution of the North Sea.Water Sci Technol1991;24:239-49

[25] Lv X,Zuo Z,Huang X.Microplastics in a municipal wastewater treatment plant: fate, dynamic distribution, removal efficiencies, and control strategies.J Clean Prod2019;225:579-86

[26] Akarsu C,Gökdağ K,Sanchez-Vidal A.Microplastics composition and load from three wastewater treatment plants discharging into Mersin Bay, north eastern Mediterranean Sea.Mar Pollut Bull2020;150:110776

[27] Liu X,Di M,Wang J.Transfer and fate of microplastics during the conventional activated sludge process in one wastewater treatment plant of China.Chem Eng J2019;362:176-82

[28] Bayo J,López-Castellanos J.Microplastics in an urban wastewater treatment plant: the influence of physicochemical parameters and environmental factors.Chemosphere2020;238:124593

[29] Yang L,Cui S,An L.Removal of microplastics in municipal sewage from China’s largest water reclamation plant.Water Res2019;155:175-81

[30] Talvitie J,Koistinen A.Solutions to microplastic pollution - removal of microplastics from wastewater effluent with advanced wastewater treatment technologies.Water Res2017;123:401-7

[31] Li X,Mei Q.Microplastics in sewage sludge from the wastewater treatment plants in China.Water Res2018;142:75-85

[32] Murphy F,Carbonnier F.Wastewater treatment works (WwTW) as a source of microplastics in the aquatic environment.Environ Sci Technol2016;50:5800-8

[33] Mitrano DM,Frehland S,Cingolani A.Synthesis of metal-doped nanoplastics and their utility to investigate fate and behaviour in complex environmental systems.Nat Nanotechnol2019;14:362-8 PMCID:PMC6451641

[34] Schmiedgruber M,Mitrano DM.Mechanistic understanding of microplastic fiber fate and sampling strategies: synthesis and utility of metal doped polyester fibers.Water Res2019;155:423-30

[35] European Commission. Urban wastewater. Available from: https://environment.ec.europa.eu/topics/water/urban-wastewater_en. [Last accessed on 25 Apr 2024]

[36] A 253 Microplastics in wastewater, wastewater sludge and soil. 2020. (in Norwegian) Available from: https://va-kompetanse.no/butikk/a-253-mikroplast-i-avlopsvann-avlopsslam-og-jord/. [Last accessed on 25 Apr 2024]

[37] Nizzetto L,Langaas S.Are agricultural soils dumps for microplastics of urban origin?.Environ Sci Technol2016;50:10777-9

[38] Ljung E,Andersson PG. Microplastics in the ecosystem. (in Norwegian). Available from: https://www.svensktvatten.se/contentassets/7be8e202754e4011a400bcff4ed89b1c/mikSVu-rap-8-13.pdf. [Last accessed on 25 Apr 2024]

[39] Regulation on organic fertilizers and related products. (in Norwegian) Available from: https://lovdata.no/dokument/SF/forskrift/2003-07-04-951. [Last accessed on 25 Apr 2024]

[40] Zhang Y,Allen S,Gao T.Atmospheric microplastics: a review on current status and perspectives.Earth Sci Rev2020;203:103118