Identification of microplastic in effluents of waste water treatment plants using focal plane array based micro Fourier transform infrared imaging.
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 mm. In all effluents MP was found with quantities ranging from 0 to 5 x 101 m 3 MP 500 mm and 1 x 101 to 9 x 103 m 3 MP 500 mm. By far, polyethylene was the most frequent polymer type in both size classes. Quantities of synthetic fibres ranged from 9 x 101 to 1 x 103 m 3 and were predominantly made of polyester. Considering the annual effluxes of tested WWTPs, total discharges of 9 x 107 to 4 x 109 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.
Water research