The role of wastewater treatment plants in surface water contamination by plastic pollutants

Abstract

The aim of this paper was to review the literature data regarding the physico-chemical characteristic of plastic pollutants discharged with municipal sewage, the practical possibility of removing microplastic particles from wastewater during different treatment steps in WWTPs and the problem of surface water contamination within them. Microplastics (the size range of 1 nm to < 5 mm), have been recognized as an emerging threat, as well as an ecotoxicological and ecological risk for water ecosystems. Municipal wastewater treatment plants (WWTPs) are mentioned as the main point sources of microplastics in an aquatic environment. Microplastic particles can be effectively removed in the primary treatment zones via solids skimming and sludge settling processes. Different tertiary treatment processes such as: gravity sand filtration, discfilter, air flotation and membrane filtration provide substantial additional removal of microplastics, and the efficiency of wastewater treatment process can be at a removal level of 99.9%. Nevertheless, given the large volumes of effluent constantly discharged to receivers, even tertiary level WWTPs may constitute a considerable source of microplastics in the surface water.

The occurrence of microplastics in freshwater systems – preliminary results from Krakow (Poland)

“…Microplastics present in the aquatic environment reach it mainly from the land. They can be in the form of waste, which will become fragmented due to UV radiation, mechanical abrasion and biological degradation (Dris et al 2015b) or come from wastewater treatment plants (Mrowiec 2018) and are in the form of microbeads from cleansing gels or fibres from washing synthetic clothes (Lončarski et al 2018). It has been shown that washing machines can generate over 1,900 plastic fibres in the single cycle (Browne et al 2011).…”

The effect of urban point source contamination on microplastic levels in water and organisms in a cold‐water stream

“…To answer these questions, we collected samples above, within, and below the city of River Falls, the only city in the otherwise predominantly agricultural watershed. Because the potential for plastic particles to enter food webs increases with decreasing size (Mrowiec 2018), we used analytical methods that allowed for the detection of particles down to ~10 μm in length.…”

Microplastics with adsorbed contaminants: Mechanisms and Treatment

“…In a case study Mrowiec (2018) , although municipal WWTPs are one of the primary sources of MPs in aquatic environment, most MP particles were removed through the primary treatment zones (e.g., solid skimming and sludge settling processes), followed by additional removal through tertiary treatment processes including membrane filtration and dissolved air flotation (DAF). However, due to a continuous intake of large volumes, even tertiary-level effluent may still contain a significant amount of MPs, along with smaller sizes (e.g., <20 μm) of MPs and MP fragments (e.g., NPs).…”