Fate of microplastics in wastewater treatment plants and their environmental dispersion with effluent and sludge.

A review of the removal of microplastics in global wastewater treatment plants: Characteristics and mechanisms

Wastewater treatment plants (WWTPs) are an important route for microplastics to enter aquatic environments. Microplastics have been recently identified in sewage samples in Russia, Sweden, France, Finland, USA, UK, Netherlands, Germany, Canada, Australia, Italy, Turkey, Denmark, Poland, China and South Korea. The aim of this study was to examine and quantify the removal efficacy of microplastics by WWTPs. Experimental methods employed in sampling, analysis and quantification of microplastics vary widely between studies. Microplastic removal rates in 21 studies were compared. Secondary and tertiary WWTPs removed an average of 88% and 94% of microplastics, respectively. The majority of microplastics, 72% on average, were removed during preliminary and primary treatment. Calculations of the settling/floating velocities of commonly used polymers indicate that primary sedimentation removes spherical particles >27–149 μm in diameter, depending on the polymer in question. Thus, the majority of microplastics removed during wastewater treatment are likely to be present in sewage sludge. Although the removal of microplastics is high, WWTPs are still an important entry point into aquatic and terrestrial systems, given the high volumes involved and the amount of sludge reused via land application. The major concerns are with small particles (especially <∼150 μm) in discharged wastewater effluent and the impact that particles which accumulate in sewage sludge may have on terrestrial ecosystems.

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Microplastics removal in wastewater treatment plants: a critical review

Microplastic pollutes water, land, air, and groundwater environments not only visually but also ecologically for plants, animals, and humans. Microplastic has been reported to act as vectors by sorbing pollutants and contributing to the bioaccumulation of pollutants, particularly in marine ecosystems, organisms, and subsequently food webs. The inevitable exposure of microplastic to humans emphasises the need to review the potential effects, exposure pathways, and toxicity of microplastic toward human health. Therefore, this review was aimed to reveal the risks of pollutant sorption and bioaccumulation by microplastic toward humans, as well as the dominant types of pollutants sorbed by microplastic, and the types of pollutants that are bioaccumulated by microplastic in the living organisms of the marine ecosystem. The possible factors influencing the sorption and bioaccumulation of pollutants by microplastic in marine ecosystems were also reviewed. The review also revealed the prevailing types of microplastic, abundance of microplastic, and geographical distribution of microplastic in the aquatic environment globally. The literature review revealed that microplastic characteristics, chemical interactions, and water properties played a role in the sorption of pollutants by microplastic. The evidence of microplastic posing a direct medical threat to humans is still lacking albeit substantial literature has reported the health hazards of microplastic-associated monomers, additives, and pollutants. This review recommends future research on the existing knowledge gaps in microplastic research, which include the toxicity of microplastic, particularly to humans, as well as the factors influencing the sorption and bioaccumulation of pollutants by microplastic.

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Phuong Linh Ngo

Papers

Pathway, classification and removal efficiency of microplastics in wastewater treatment plants