University of Guilan Caspian Journal of Environmental Sciences 1735-3033 17 4 2019 12 01 Comparative life cycle assessment of municipal wastewater treatment systems: lagoon and activated sludge 327 336 3806 10.22124/cjes.2019.3806 EN Marzieh Mohammadi Department of Environmental Sciences and engineering, Ardabil Branch, Islamic Azad University, Ardabil, Iran Ebrahim Fataei Department of Environmental Sciences and engineering, Ardabil Branch, Islamic Azad University, Ardabil, Iran Journal Article 2020 01 03 Providing health conditions, prevention of water pollution and wastewater reuse are needed to select the best wastewater treatment process before designing and implementing, according to regional climatic conditions. the aim of the present study was to evaluate the lagoon and activated sludge wastewater treatment systems using life cycle assessment and ISO14040 standards within four steps. Required data in the study systems were matter and energy inputs, including NH<sub>3</sub>-N, TP, TN, CL, O<sub>2</sub> and electricity, as well as pollutant outputs involving BOD5, COD, SS, NH3-N, TP, TN, CL, CO<sub>2</sub>, and CH<sub>4</sub>. The data were obtained from treatment systems of Ardabil (aerated lagoon) and Tabriz (activated sludge), Iran. Some of the data were obtained by calculation and the eco-invent database was used to complete the information required. Data were analyzed by Simapro 8.0.1 software. The results of the study demonstrated that the lagoon system in comparison with the other systems had 100% negative impacts in every effect classes, while the activated sludge system on global warming (6.39%) and photochemical oxidation (7.14%) had the least impact. Therefore, the lagoon system was recognized as the environmentally-harmful system, while the activated sludge as the best wastewater treatment system. Activated sludge Aerated lagoon Effect classes Environmental impact Life cycle assessment Wastewater https://cjes.guilan.ac.ir/article_3806_56805ae339ae8d2b41dea6b711e54e61.pdf