An evaluation of microplastics fate in the wastewater treatment plants: frequency and removal of microplastics by microfiltration membrane

Abstract In this research, the fate and removal of microplastics (MPs) entering and leaving a wastewater treatment plant (WWTP) was investigated. Additionally, application of the microfiltration membrane technique for MPs removal was evaluated. In the first phase, the quantity, type and size of the MPs were studied from three different points of the WWTP. The results showed that the average amount of MPs entering into the WWTP, accumulated in the sludge matrix and discharged from the effluent were 206, 183 and 94 MP/L, respectively. The MPs were observed mainly in the forms of fibers, pellets, and fragments, with a proportion of 35%, 39%, 22%, and 34%, 22%, 38%, and 31%, 39%, 37.7% in the influent, effluent and sludge of the WWTP, respectively. It should be noted, a minor amount of foam (2%) and film (0.3%) was also observed. The particle size distribution of the MPs in the effluent of the system was almost identical (6–14% for 1–5,000 μm), while the influent mostly contained particles within 1–100 μm (above 26%) with other particle sizes within 100–5,000 μm (8–17%). Particle size within a range of 500–5,000 μm was abundant in the sludge. In the second phase, a micro-filtration (MF) membrane with a pore size of 0.1 μm was applied to eliminate the MPs from the WWTP effluent. It was observed the application of the MF membrane technique could achieve MPs removal efficiency up to 98% in the effluent of the system.