Wastewater treatment plants as a pathway for the release of microplastics into the environment: Investigation of sludge and treated effluent of Sari wastewater treatment plant

Document Type : Research Article


1 Department of Environmental Pollution, Institute of Environmental Sciences, Shahid Beheshti University, Tehran, Iran

2 Department of Environmental Technologies, Environmental Sciences Research Institute, Shahid Beheshti University


Problems caused by the widespread presence of microplastics in the environment have attracted the attention of many researchers. Urban wastewater treatment plants are considered as one of the main releasing sources. In this study, Sari municipal wastewater treatment plant was investigated as one of the potential sources of contaminating aquatic ecosystems (Tajan River and the Caspian Sea) and terrestrial. The samples from effluent and sludge were taken with 3 replications, in April and June 2018. The effluent samples were passed through 500, 300 and 37 μm steel sieve. Organic materials in the sludge and effluent samples were digested using hydrogen peroxide. Then, microplastics were extracted based on the density separation technique by sodium iodide salt and analyzed using a stereomicroscope and micro-Raman. The average number of microplastics in the effluent was 423.4 per cubic meters, of which more than 77% were fiber and the dominant size of microplastics was 37-300 μm. Also, sewage sludge had an average of 128.8 microplastic per gram (dry weight), mostly in fiber form (87.5%). Examination of the microplastics structure showed that fibers were mainly polyester (effluent 40% and sludge 59%), whereas the majority of particles were polyethylene (effluent 73% and sludge 68%), which are mainly due to the wastewater of washing clothes and microbeads used in cosmetics. Therefore, considering the amount of microplastics present in the effluent and sludge, Sari wastewater treatment plant can be considered as one of the most important sources for the release of microplastics in the aquatic and terrestrial ecosystem in the north of the country.


Main Subjects

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