Sustainable Calcium Sourcing through Marine Resources: Enhancing Microbially Induced Carbonate Precipitation for Coastal Sand Stabilization

To address the issue of difficult transportation of construction materials in foundation reinforcement and slope protection projects in island reef or coastal regions, the bipolar membrane electrodialysis system is employed to generate hydrochloric acid from simulated concentrated seawater. The hydrochloric acid is then used to dissolve the calcareous sand on the island reefs or the shells on the beach, thereby obtaining self-made calcium sources required for Microbially Induced Carbonate Precipitation (MICP) reinforcement. These self-made calcium sources are respectively utilized for the MICP treatment of calcareous sand and siliceous sea sand. By comparison with chemically pure calcium sources and through separate MICP aqueous solution tests and sand column reinforcement tests, the applicability and strengthening performance of the self-made calcium sources were investigated. The results indicated that hydrochloric acid generated by the bipolar membrane electrodialysis device could dissolve calcareous sand and shells, obtaining Ca 2+ solutions of 1.52 mol/L and 1.56 mol/L, respectively. These solutions were diluted before being applied in the bio-cementation process. When Ca 2+ ions derived from the dissolution of calcareous sand were used for MICP reinforcement of calcareous sand, the unconfined compressive strength reached 2.1 MPa, compared with 770.1 kPa for the chemically pure CaCl 2 control. Simultaneously, when the Ca 2+ derived from dissolving shells was employed for the reinforcement of siliceous sea sand, the unconfined compressive strength was 533.1 kPa, compared with 198.9 kPa for the chemically pure CaCl 2 control. Further analysis revealed that ions such as Mg 2+ , Al 3+ , and Fe 3+ present in the self-made solutions can alter the morphology and composition of the precipitated minerals, resulting in a better reinforcement effect than that of the chemically pure CaCl 2 solution group. This study provides a sustainable approach to calcium sourcing for bio-reinforced sand by utilizing marine and island resources, with significant economic value and application potential.