Occurrence of microplastics in influent, sewage sludge and effluent of municipal wastewater treatment plant, A case study center of Iran, Qom city

<title>Abstract</title> The presence of Microplastics (MPs) in the environment is a serious threat to the health of humans and ecosystems. One common source of environmental MPs pollution is the sludge and effluent discharged by wastewater treatment facilities. Typically, there are no specific measures to remove MPs in treatment plants. The purpose of this study is to investigate the presence of MPs in the inlet wastewater, outlet effluent, and sludge of one of the wastewater treatment plants of Qom city in Iran. Monthly sampling was done in the spring and summer of 2022. A total of 18 samples were obtained from wastewater, effluent, and sludge. MPs were identified and separated according to valid guidelines. MPs were subjected to SEM and µ-Raman analysis for further investigation. The average MPs in wastewater and effluent were 710 ± 34.67 and 51 ± 4.42 (MPs/L), respectively, while it was 30.76×10³ (MPs/kg) in sludge. The average removal efficiency of MPs in the treatment plant was 97.6%. Overall, polyethylene terephthalate and fibers were the most frequent in the samples. Dominant sizes of MPs in wastewater and sludge were 250–500 µm, while their size in effluent was 250 − 100 µm. Considering the results, it is estimated that 2652×10⁶ MPs enter the environment through effluent every day and can lead to air, soil, and surface water pollution. It makes the need for decisions at the international level to reduce the production and consumption of plastics more necessary.