A new study published in Engineering outlines an integrated framework for achieving carbon neutrality in wastewater treatment plants (WWTPs), combining energy efficiency, greenhouse gas mitigation, energy recovery, and resource recovery to support global climate goals. The research indicates that WWTPs must adopt a multifaceted strategy to balance effluent quality requirements with reduced energy consumption and lower carbon emissions across direct, energy-related, and indirect emission scopes.

Improving energy efficiency stands as a foundational step, starting with optimizing existing facilities. Aeration accounts for the largest share of energy use in typical WWTPs, followed by pumping and sludge treatment. Implementing smart monitoring and process control, such as dynamic aeration regulation and variable-speed drive compressors, can effectively lower energy demand without compromising treatment performance. Meanwhile, novel low-carbon processes offer substantial potential for energy savings, including anammox-based systems, aerobic granular sludge, and membrane aerated biofilm reactors. These technologies reduce energy requirements linked to aeration, pumping, and sludge management, with distinct advantages suited to different wastewater characteristics and regional conditions.

Minimizing greenhouse gas emissions is equally critical, especially for methane and nitrous oxide, which possess much higher global warming potential than carbon dioxide. Methane emissions mainly arise from sludge treatment units, while nitrous oxide is closely associated with nitrogen conversion processes. Targeted operational adjustments and process optimization can help curb these fugitive emissions, though long-term prediction of nitrous oxide release remains challenging.

For energy recovery, the study highlights two major pathways: harnessing energy from sewage sludge and recovering heat from treated effluent. Anaerobic digestion generates biogas that can be used for on-site power and heat, while sludge incineration converts organic matter directly into heat. Notably, effluent heat recovery holds far greater energy potential than biogas utilization, though its incentive structure varies by region.

Beyond energy, the research emphasizes shifting WWTPs toward resource recovery facilities. Organic carbon, nitrogen, and phosphorus in wastewater can be recovered as high-value products such as biopolymers and nutrients, offering broader societal benefits than energy autonomy alone. While organic carbon allocation creates trade-offs between energy and material production, chemical recovery often delivers stronger economic and environmental value.

The study concludes that carbon neutrality in wastewater treatment requires coordinated actions across multiple dimensions. Prioritizing energy minimization in existing plants, deploying low-carbon technologies, controlling potent greenhouse gases, unlocking effluent heat, and scaling resource recovery together form a practical roadmap toward sustainable, low-carbon wastewater management.

The paper “Path to Carbon Neutrality in Wastewater Treatment—From Energy Optimisation to Resource Recovery,” is authored by Bohan Yu, Eveline I.P. Volcke, Xiaodi Hao, Mark C.M. van Loosdrecht. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.12.005. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.