Potential of using nature-based solutions to upgrade wastewater treatment plants in China and reduce carbon emissions: A comparative study of advanced treatment processes and constructed wetlands

Abstract

Constructed wetlands (CWs) offer a nature-based solution for upgrading wastewater treatment plants (WWTPs). However, the carbon reduction potential of CWs, compared to commonly used advanced treatment processes, remains unclear. In this study, we assess the greenhouse gas (GHG) emissions of six upgrading processes through life cycle assessment across 4,179 WWTPs in China. Results suggest that additional GHG emissions from WWTPs upgrading range from 0.14 to 0.43 kg of carbon dioxide equivalents (CO₂eq) per cubic meter of treated wastewater. Vertical subsurface flow CWs could avoid GHG emissions by 33.8 % to 66.9 % compared to advanced treatment processes. However, surface flow and horizontal subsurface flow CWs do not exhibit carbon reduction potential in northern provinces. Energy consumption is identified to be the main contributor to GHG emissions in most processes. Our findings highlight the importance of optimizing energy structures and developing region-specific strategies to minimize GHG emissions during WWTP upgrading.