Document Type : Research Paper
Authors
1
Environmental Engineering Group, Aras International Campus, University of Tehran, Jolfa, Iran. E-mail: Ahmadinezhad.mojtaba@gmail.com
2
Corresponding author,Department of Environmental Engineering, Faculty of Environment, University of Tehran, Tehran, Iran. E-mail: mehrdadi@ut.ac.ir
3
Department of Environmental Engineering, Faculty of Environment, University of Tehran, Tehran, Iran. E-mail: ghhendi@ut.ac.ir
4
Department of Environmental Engineering, Faculty of Environment, University of Tehran, Tehran, Iran. E-mail: mjamiri@ut.ac.ir
5
Environmental Engineering Group, Aras International Campus, University of Tehran, Jolfa, Iran. E-mail: enmehrdadi@ut.ac.ir
10.22059/jes.2025.389452.1008580
Abstract
The development of low-carbon wastewater treatment plants (WWTPs) plays a crucial role in achieving peak carbon and carbon neutrality goals. This study aims to calculate the carbon footprint, energy consumption, and greenhouse gas (GHG) emissions, as well as to provide effective methods for reducing these emissions at the Sari City Wastewater Treatment Plant. This study examined data from the Sari City Wastewater Treatment Plant for the years 1400 to 1402 (Solar Hijri calendar, approximately 2021-2023). The treatment system is an activated sludge type utilizing the modified Ludzack-Ettinger (MLE) process, which is considered an advanced biological process for the removal of carbonaceous organic matter and nitrates. Carbon emissions from WWTPs are divided into two categories: direct emissions and indirect emissions.
Direct emissions include carbon dioxide (CO2 ) resulting from aerobic decomposition and the conversion of organic matter in biological treatment processes; CO2 and methane (CH4) from anaerobic digestion processes; and dinitrogen monoxide (nitrous oxide, N2O) from nitrification and denitrification processes.Indirect emissions relate to the consumption of purchased electricity for blowers, pumps, and other equipment within the WWTP, and also include emissions from the transportation of fuel consumed at the plant and other internal activities. Based on the annual electricity consumption, an average of
0.61 kWh of electricity is consumed per cubic meter (M3) of treated wastewater. The total CO2 equivalent CO2eq emissions from the Sari WWTP from 1400 to 1402 are as follows: Off-site emissions (including electricity consumption, diesel fuel, residual biological matter decomposition, sludge disposal, residual degradable matter, and dinitrogen monoxide N2O 48113.7 tons of CO2eq On-site emissions (including endogenous biomass decomposition, removal of carbonaceous biological matter, nitrification, and dinitrogen monoxide (N2O) : 1934.26 tons of CO2eq. The GHG emission rate per cubic meter of treated wastewater at the Sari WWTP was calculated as follows:Year 1400: 0.071 Kg CO2eq, Year 1401: 0.078 kg CO2eq , Year 1401: 0.078 kg CO2eq. These results indicate an increase in emissions from 0.071 to 0.078 kg CO2eq
from the year 1400 to 1402. High energy consumption and inadequate sludge management are the primary sources of indirect emissions, while the incoming organic load and biological processes, including nitrification and denitrification, are the most significant factors contributing to direct GHG emissions. To mitigate emissions, it is essential to optimize electricity consumption, utilize renewable energies, upgrade primary sedimentation, and improve sludge management. In summary, process modifications, energy optimization, and macro-level policies can contribute to a meaningful reduction in greenhouse gas emissions.
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