(533y) Understanding the Transport and Fate of the Microplastic Particles in a Main Wastewater Treatment Plant: Case Study of a Typical Plant in Western Iran

Large quantities of microplastics (MPs) are thought to be globally discharged to the freshwater environments through wastewater treatment plants (WWTPs). However, the information available related to sources of contamination is limited. This case study focusses on understanding the role of water effluent and sludge from a municipal WWTP (located in Western Iran) as potential pathways for MPs input into the both aquatic and agriculture-based environments. The Sanandaj’s WWTP has a large daily treatment capacity and serves about 500,000 residents. Samples from different plant locations were taken: For example, from influent, grit removal chamber outflow, primary effluent, and secondary effluent. Sludge samples were also collected and investigated to evaluate the potential risk associated with the application of dried sewage sludge as fertilizer in agricultural soils. Samples were filtered through a set of sieves in laboratory and, afterward, they were counted and classified according to their shape and size by means of visual investigation using a stereomicroscope. The results showed that the most dominant particles were fibers followed by fragments. Furthermore, Fourier-transform infrared spectroscopy (FTIR) was used to confirm that the plastic originated from suspected particles. The MPs concentration ranged from 163 MPs/L in influent, that measures up to an annual arrival of 595× 10 ¹⁰ MPs into the plant, to 8.4 MPs/L and 96 MPs/g in effluent and dried sludge, respectively. This data indicates that even though the MPs separation efficiency of the plant was high (>90%), approximately 30.7× 10 ¹⁰ and 67.3× 10 ¹⁰ MPs are released into the receiving environment each year by dissemination of final effluent and dried sludge, respectively. One key outcome of the current case study is confirming the presence of MPs in WWTP (such as Sanandaj’s) effluent and sewage sludge. Moreover, the study indicates that WWTPs could be an important pathway by which MPs are introduced to the marine and terrestrial environments. The present case can be duplicated in other WWTP in different locations and validate the trend so that treatment procedures can be identified for minimizing or preventing the discharge of MP to water streams.