A Possible Path Toward Profitable Carbon Removal: A Techno-Economic Analysis on Combined Ocean Alkalinity Enhancement and Waste Concrete Upcycling

Electrochemical ocean alkalinity enhancement (E-OAE) is a promising carbon removal technique that leverages waste brine from desalination plants. Using green electricity, it converts this brine into a base for ocean alkalinization and a hydrochloric acid byproduct. While promising for negative emission, the large volume of acid produced creates a significant management challenge. This work presents the technical and economic details of a novel approach to upcycle waste concrete using the E-OAE acid byproduct. The proposed process utilizes the dilute hydrochloric acid byproduct to treat coarse recycled concrete aggregates (RCA) in an acid-recirculating rotary drum reactor, thereby recovering high-quality aggregates for resale and adding additional value to E-OAE. This combined process addresses the dual challenges of managing significant construction and demolition waste and mitigating the management issues associated with acidic byproduct from E-OAE systems. The techno-economic analysis highlights the strong financial viability of this approach. For a plant processing 1,000 metric tons of RCA per day—a scale that utilizes the acid byproduct from an E-OAE facility sequestering 27,000 tons of CO2 annually—the estimated capital cost is $26.8 million. With projected revenues of $13 million from aggregate sales and tipping fee equivalence against $7.8 million in operating costs, the facility generates a net return of $5.2 million. This corresponds to a 5-year payback period and a significant net profit of $194 per ton of CO2 removed, based on the plant profit alone without accounting for carbon credits. This integrated approach offers a sustainable, economically compelling pathway for carbon removal and circular waste management.