Efficiency of Wastewater Treatment Plants (WWTPs) for Microplastic Removal: A Systematic Review

Plastic is widely used for human activities (food packaging, medical, technological devices, etc.) and there is a growing concern regarding the risks for environmental and human health because they have still not been fully evaluated. Particularly, microplastics (primary and secondary) are present in all environmental compartments and this poses a potential threat because of their entry into the food chain. Furthermore, microplastics can absorb numerous pollutants that can be accumulated in the human body through bioaccumulation and biomagnification processes. We carried out a systematic review using a PRISMA approach to verify the efficiency of wastewater treatment plants (WWTPs) for microplastic removal. The international databases (PubMed, Science Direct, Scopus) were used to find published studies on efficiency of wastewater treatment plants (WWTPs) for microplastic removal. The search period was between January 2010 and June 2020. Over 1000 full research papers were initially selected through the use of keywords. After that, the papers were further selected by English language, title, and abstract, and duplicate papers and non-relevant papers were eliminated according to eligibility criteria. Finally, we included 15 full research papers. In each of the 15 full research papers selected, the microplastics identified were categorized by the authors for shape, size, and type of polymers identified. The characterization of the various types of microplastics was performed by Fourier Transform Infrared Spectroscopy (FTIR) or Raman spectroscopy. We have observed how wastewater treatments plants located in different continents (Europe, Asia, North America) mostly use a primary and secondary type of treatment that allows one to reach a high percentage of microplastics removal from wastewater. Most of the wastewater treatments plants investigated reported a microplastics removal efficiency greater than 90%, but despite this, millions of microplastics continue to be released every day into the aquatic environment. Then, in the near future, efficient and common standardized protocols for monitoring MPs should be drawn up, as well as increasing the knowledge of sources and strategies to further reduce microplastics contamination of treated wastewater.