Identification and Analysis of Plastic Microparticles in the Inlet and Outlet of the Wastewater Treatment Plant and Investigation of the Relationship between Different Seasons of the Year with the Amount of Production and Emission of Particles

Microplastics are found in various environments with the increasing use of plastics worldwide. These particles can cause serious injuries. These damages not only affect water, soil, and air but also can cause irreversible problems for human beings and other living creatures. According to this, sampling, separation, detection, and characterization of microplastics (MPs) dispersed in water and wastewater bodies are a challenging and critical issue for a better understanding of the hazards for the environment posed by such nearly ubiquitous and still largely unknown form of pollution. Plastics can exist in different forms in nature, among which microplastics are extremely harmful. Importantly, conventional wastewater treatment plants cannot remove microplastics and drain them into the aquatic and terrestrial accepting environments, which in turn can endanger living creatures. Therefore, the studies oriented to their detection and extraction are of great importance. In the present study, an optimized method is introduced to efficiently detect and extract microplastics from the input effluent and output waste streams of the wastewater treatment plants. First, the seasonal sampling was performed in three seasons: spring, summer, and autumn, to determine the season with the most microplastic production. Then, the acid washing using the 30% hydrogen peroxide (H2O2) and 0.05 M divalent iron was performed on the prepared samples. Also, since this method is based on creating density gradient, the sodium iodide (NaI) salt was used. Notably, the performance of the studied wastewater treatment plant in terms of the microplastic removal efficiency was also evaluated using this method. Accordingly, the wastewater treatment plant was able to remove microplastics by 94–96%, which means that about 5% of the residual microplastics are drained into the aquatic and terrestrial environments. Moreover, it was revealed that microfibers have a lower percentage of removal in wastewater treatment process than microparticles. The result of the method used has shown that more than 95% of the particles can be detected.