Study on presence of microplastic pollution in the wastewater treatment plant of district 22 of Tehran

Wastewater treatment plants are known as an important source of microplastics. Though a major proportion of microplastics are removed in wastewater treatment plants, the effluent of plants contain a significant amount of microplastic particles which eventually release into the environment. Until now there is no investigation on the role of wastewater treatment plants on the release of microplastics in Tehran. This study aims to assess the discharge amount of microplastic particles from wastewater treatment plant in district 22 of Tehran. Sampling was conducted from the influent and effluent of the plant with grab method and sieving through 300, 105 and 25 µm stainless still filters.  Retained samples were treated to remove organic and inorganic materials. Then particles were detected, counted and analyzed under microscope (*10). Results indicate that treatment process has a significant impact on microplastic particles removal. After the treatment process, the average of 2.15 MP/liter were found in the effluent. Larger particles were removed effectively (at the size of ≥300 and 105-300 µm) and smaller particles (25-105 µm) indicated a higher abundance. Among the detected particles fibers had the highest abundance and then fragment were at the second order. This finding indicates that waste water treatment plants can act as a source for microplastic pollution in the urban environment.