Enzymatic seawater mineralization for sustainable soil stabilization and algal biomass production

Soil stabilization is a crucial countermeasure to mitigate marine sediment erosion and scour-related hazards. This study develops a novel method for reinforcing sandy soils in seawater environments via enzymatically induced seawater mineralization, while mitigating bio-generated ammonium contamination through algae cultivation. Unlike traditional bio-cementation methods relying on lab-graded calcium reagents, the proposed approach utilizes naturally occurring calcium and magnesium in seawater to induce carbonate precipitation. Results showed that soybean-extracted urease still exhibited favorable mineralization potential despite a 10% activity inhibition by dissolved salts. A dual-stage cementation treatment was proposed, involving urease fixation followed by continuous injection of seawater-based urea solution. After six cycles of dual-stage treatment, soil samples achieved a maximum unconfined compressive strength of 2.83 MPa. Key factors influencing cementation efficacy during the treatment included urease fixation efficiency, continuous injection rate and ambient temperature. Microscale analysis revealed that soil strength enhancement was mainly attributed to interparticle precipitates of aragonite and magnesium calcite. Moreover, ammonium-rich effluent from the bio-treatment served as a nutrient source for algae growth, reducing ammonium levels by 68.3% within 25 days. This study suggests that enzymatically induced seawater mineralization combined with algae cultivation would provide a sustainable pathway for soil stabilization in marine environments.