Ocean Alkalinity Enhancement (OAE) is recognized as a highly promising marine carbon dioxide (CO₂) removal technology. Recently, the research group led by Professor Liu Jihua from the Institute of Marine Science and Technology, Shandong University, has made significant progress in this field by systematically evaluating the carbon sequestration efficiency and potential of an innovative wastewater-based OAE approach. Their study, “The potential of wastewater treatment on carbon storage,” was published in Science Advances. Professor Liu Jihua is the corresponding author, and Dr. Zheng Liwen is the first author. Shandong University is the primary institution affiliated with this work.

The “wastewater-based OAE” concept leverages the unique chemical environment inherent in wastewater treatment processes, characterized by low pH, high CO₂ concentrations, and organic acids, to theoretically promote the dissolution of alkaline minerals, such as olivine. The alkaline mineral dissolution, in turn, increases water alkalinity and enhances CO₂ absorption. Prof. Liu’s team investigated CO₂ generation during aerobic wastewater treatment, simulating the alkalization process with olivine. Their results showed that aerobic treatment significantly accelerated olivine dissolution. The alkalization efficiency achieved was nine times greater than that observed in non-biologically treated wastewater and 20.5 times higher than the olivine dissolution rate in seawater under similar conditions. Adding olivine to aerobically treated wastewater significantly enhanced the total alkalinity of the effluent to over 10 mmol kg⁻¹, while also improving phosphate removal.

Building on these findings, the team assessed the global carbon sequestration potential of this wastewater-based OAE strategy. By analyzing 9,480 wastewater treatment plants (WWTPs) located within 10 km of global coastlines and applying constraints based on environmental regulations and seawater carbonate saturation, they concluded that coastal WWTPs alone could facilitate a net carbon sink of approximately 18 million tons of CO₂ annually. Geographically, while higher potential exists in high-latitude cold water regions, about 79.3% of this potential is concentrated in the mid-latitude areas of the Northern Hemisphere (20°N-60°N), where WWTPs are densely situated. The European Union, the United States, and China collectively account for 55.8% of this potential.

This research experimentally validates the improved efficiency of the “wastewater-based OAE” method in dissolving alkaline minerals and enhancing carbon sequestration. It presents the first quantitative global assessment of its potential and identifies key regions for deployment within realistic constraints. This study offers a strong scientific foundation for advancing OAE technologies to address climate change. This research experimentally validates the improved efficiency of the “wastewater-based OAE” method in dissolving alkaline minerals and enhancing carbon sequestration. It presents the first quantitative global assessment of its potential and identifies key regions for deployment within realistic constraints. This study offers a strong scientific foundation for advancing OAE technologies to address climate change.

This work was supported by the Global Ocean Negative Carbon Emissions (Global-ONCE) program and the Hainan Provincial Financial Support Project.

Fig 1 Global potential of wastewater-based Ocean Alkalinity Enhancement (OAE) for carbon sequestration

(A) Framework for estimating the carbon sequestration potential of current WWTPs via OAE and its global distribution, (B) latitudinal distributions of artificial alkalinity addition in wastewater, (C) carbon sequestration potential of wastewater-based OAE, and (D) carbon sequestration potential of wastewater-based OAE in the top 10 countries.