Alkalinity Factory Can Achieve Positive Climate Benefits Within Decades.

Ocean alkalinity enhancement (OAE) is a thriving pathway to mitigate climate change, in which the alkalinity factory promises controllable environmental impacts and cost-effective monitoring, reporting, and verification (MRV). However, there remains a research gap in the identification of climate benefits of alkalinity factory, which is essential to locate the human efforts to mitigation. Our study employed life cycle assessment (LCA) to evaluate climate contribution from carbon removal potentials and environmental footprints of an alkalinity factory, named the Marine Alkalinity Reinforcement System (MARS). The results indicated that MARS could capture an average of 153.5 tons of CO2 over its lifespan, achieving a net efficiency of 84.7% with olivine as the alkalinity source. Primary sources of the environmental footprint included olivine production, treatment tank manufacturing, and implementation activities. Consequently, the emissions generated during MARS’s lifespan necessitate carbon emission payback periods of 1.9 to 2.7 years and total environmental footprint payback periods of 6.8 to 9.5 years. Additionally, the carbon removal potential and efficiency of MARS were predominantly dominated by olivine particle size and olivine-to-seawater ratio. Ultra-fine olivine (5 μm) and a high olivine-to-seawater ratio (4:1) significantly increased the seawater treatment rate but also resulted in high olivine comminution energy consumption and present engineering challenges. Our analysis demonstrated that a medium-sized (50 m³) MARS filled with 25 μm olivine is recommended to reduce emissions per ton of CO2 capture and environmental payback periods. Our findings reveal that alkalinity factory is a viable solution in marine carbon dioxide removal when configurations are well-designed to ensure positive environmental benefits in its lifespan.