Greenhouse gas emissions from municipal wastewater treatment: Global insights and Vietnam's approach

Abstract

Greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs), including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), are significant contributors to global climate change. This study addresses the lack of data in Vietnam's fragmented and under-monitored wastewater systems by integrating field measurements, dynamic modeling, and life cycle assessment (LCA) to quantify GHG emissions from 29 centralized plants and multiple decentralized systems. The results indicate that CH₄ and N₂O emissions amount to 378 and 79.7 million tons of CO₂-equivalent annually, with local emission factors significantly exceeding the IPCC Tier 1 defaults. Methane is primarily produced from anaerobic sludge digestion and septic tanks, while N₂O arises from nitrogen removal processes under low dissolved oxygen (DO) conditions. Indirect CO₂ emissions from electricity and fuel consumption contribute an additional 17 % to the sector's GHG footprint. Technologies such as Johkasou, Anammox, and biogas recovery demonstrate strong mitigation potential, with Johkasou reducing emissions by approximately 16 % and Anammox lowering N₂O outputs. Additional solutions including photovoltaic (PV) systems, machine learning-based process optimization, and microbial fuel cells (MFCs) offer promising pathways for operational efficiency and long-term sustainability. These findings provide critical inputs for Vietnam's carbon market implementation and align with global efforts to improve the accuracy of GHG accounting in wastewater systems.