A Comparative Review of Biological, Electrochemical, and Membrane-Based Methods for Direct Ocean Carbon Capture.

Direct ocean carbon capture (DOC) has emerged as a promising strategy for mitigating atmospheric CO2 levels and addressing ocean acidification. Unlike direct air carbon capture methods, DOC leverages the ocean's vast carbon storage capacity, offering a scalable and efficient route for carbon dioxide removal. This systematic comparative review categorizes existing DOC methods into three types: (1) biological carbon capture, which relies on photosynthesis by microalgae and marine microorganisms; (2) electrochemical carbon capture, which utilizes water electrolysis to generate H+ and OH- ions for pH-driven CO2 removal; and (3) physical carbon capture, which employs hollow fiber membranes to directly separate CO2 from seawater. For each technology, we evaluate efficiency, energy consumption, cost, technology readiness level (TRL), scalability, and major challenges. By integrating recent pilot data and providing a critical assessment, this review offers a roadmap for future research in direct seawater CO2 capture. The comparative analysis reveals that electrochemical methods achieve the highest efficiency (60-85%) but face membrane fouling and electrode degradation challenges, while biological methods offer low-energy operation but suffer from slow kinetics and high harvesting costs, and membrane-based methods provide high removal rates (up to 94%) but require improved fouling resistance.