Identification of microplastic in effluents of waste water treatment plants using focal plane array-based micro-Fourier-transform infrared imaging

Abstract

The global presence of microplastic (MP) in aquatic ecosystems has been shown by various studies. However, neither MP concentrations nor their sources or sinks are completely known. Waste water treatment plants (WWTPs) are considered as significant point sources discharging MP to the environment. This study investigated MP in the effluents of 12 WWTPs in Lower Saxony, Germany. Samples were purified by a plastic-preserving enzymatic-oxidative procedure and subsequent density separation using a zinc chloride solution. For analysis, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FT-IR) and focal plane array (FPA)-based transmission micro-FT-IR imaging were applied. This allowed the identification of polymers of all MP down to a size of 20 μm. In all effluents MP was found with quantities ranging from 0 to 5 × 10 m MP > 500 μm and 1 × 10 to 9 × 10 m MP < 500 μm. By far, polyethylene was the most frequent polymer type in both size classes. Quantities of synthetic fibres ranged from 9 × 10 to 1 × 10 m and were predominantly made of polyester. Considering the annual effluxes of tested WWTPs, total discharges of 9 × 10 to 4 × 10 MP particles and fibres per WWTP could be expected. Interestingly, one tertiary WWTP had an additionally installed post-filtration that reduced the total MP discharge by 97%. Furthermore, the sewage sludge of six WWTPs was examined and the existence of MP, predominantly polyethylene, revealed. Our findings suggest that WWTPs could be a sink but also a source of MP and thus can be considered to play an important role for environmental MP pollution.

Reference database design for the automated analysis of microplastic samples based on Fourier transform infrared (FTIR) spectroscopy

“…It was collected at waste water treatment plant Oldenburg on 13 August 2015 in front of a post-filtration unit. The (in)organic matrix was removed via enzymatic digestion [16, 17]. For comparison, the sample was re-measured in the spectral range of 3600–1250 cm −1 (original study 3200–1250 cm −1 ) [25], as described above.…”

“…Typically, the (in)organic matrix of environmental samples is reduced prior to measurement by chemical or enzymatic treatment and the residue concentrated onto filters [2, 16]. In earlier studies [13, 17, 18], the complete filter areas were measured followed by an analysis through integration of plastic polymer-specific band regions for the generation of false color images. The hereby pre-selected particles had to be compared via manual comparison to reference spectra, which is a time-consuming task [10, 11, 19] and prone to human bias.…”

Plastic pollutants in water environment

“…Among them can be distinguished: wastewater treatment plants, cargo shipping, fisheries, human waste from beaches and urban runoff [Cole et al 2011, Stolte et al 2015, Peters and Bratton 2016, Alomar et al 2016, Michielssen et al 2016, Solomon and Palanisami 2016, Graca et al 2017, Mintening et al 2017, Wright and Kelly, 2017 Baltic Sea water, which suggests that tourist activity could be a major entry path for potential synthetic fibres as well.…”

Mikroplastik in Binnengewässern

“…Kleinere oder leichtere Partikel steigen nach oben, weil ihre Sinkgeschwindigkeit geringer ist als die des aufsteigenden Mediums. Imhof et al (2012) Cole et al 2014;Mintenig et al 2014;Dris et al 2015b;Mani et al 2015;Zhao et al 2015) (Vandermeersch et al 2015), Alkali (Foekema et al 2013;Wesch et al 2016 . Ein Vergleich der Ergebnisse mit bisherigen Studien ist schwierig, da bisher nur eine Studie diese Methode mit einer chemische Analyse kombiniert hat (Maes et al 2017).…”