Wastewater treatment plants' contribution in microplastics' contamination of surface water. Effluent concentration and detection techniques review

Microplastics (MPs), recently gain notable attention since they are detected in water bodies. Increasing production and recurrent short-term usage of plastic products enhance their disposal rates. They are originated from land-based or sea-based sources related to anthropogenic activities. Wastewater treatment plants (WWTPs) and applied technologies are under investigation, as a potential source of microplastic contamination. Although typical WWTPs are found to be able to remove from 70% to more than 90% of microplastics from wastewater, these plastic particles, smaller than 5 mm, are detected in effluents. Even small concentrations of microplastics in WWTPs effluents can have a significant accumulative effect, since WWTPs release a large amount of treated wastewater continuously. It is worth mentioning that the daily discharge of microplastics from a WWTP, as estimated, can reach a few million particles. Microplastics' concentration that has been reported in effluents ranges between less than 0.5 particles/L to more than 50 particles/L. This study focuses on the contamination of surface waters from MPs, as a result of WWTPs' effluents. A thorough review of current research is targeted to summarize the reported MPs concentration measurements in the wastewater treatment processes, the WWTPs efficiency and MPs removal rates, as well as the prevailing MPs identification techniques.