Carbon Footprints of Wastewater Treatment Plants: A Comprehensive Analysis of Emission Sources and Quantification for Sequencing Batch Reactor System

Wastewater treatment plants (WWTPs) are significant contributors to anthropogenic greenhouse gas (GHG) emissions through both direct biological processes generating methane (CH₄), nitrous oxide (N₂O), and biogenic carbon dioxide (CO₂) and indirect energy consumption. This comprehensive research paper synthesizes findings from 30 peer-reviewed studies to present a holistic analysis of carbon footprints in wastewater treatment, with a specific quantitative assessment of a sequencing batch reactor (SBR) facility processing 5,000 m³/day. The analysis reveals that N₂O emissions can constitute up to 75% of a plant's carbon footprint, while aeration accounts for 40–75% of the total energy consumption. The carbon footprint of WWTPs varies by treatment technology, scale, and operational conditions, ranging from 61 to 161 kg CO₂e per population equivalent (PE) annually. For the 5,000 m³/day SBR facility, baseline emissions range from 365 to 1, 095 tCO₂e annually and can be reduced by 30–50% through anaerobic digestion with biogas recovery and anoxic phase optimization. The findings underscore that achieving carbon neutrality requires extending accounting beyond plant boundaries to include effluent exports, sludge management, and urban infrastructure integration. This paper provides a unified framework for understanding, quantifying, and mitigating carbon emissions from wastewater treatment, with particular emphasis on SBR technology.