Beach sands are composed of a variety of minerals including quartz and different carbonate minerals. Seawater in beach sand contains several ions such as sodium, magnesium, calcium, chloride, sulfate, and potassium. These variations in mineralogy and the presence of salts in beach sand may affect the treatment via enzyme-induced carbonate precipitation (EICP). In this study, set test tube experiments were conducted to evaluate the precipitation kinetics and mineral phase of the precipitates in the presence of zero, five, and ten percent seawater (v/v). The kinetics were studied by measuring electrical conductivity (EC), pH, ammonium concentration, and carbonate precipitation mass in EICP solution at different time intervals. A beach sand was also treated using EICP solution containing zero and ten percent seawater at one, two, and three cycles of treatment. Unconfined compressive strength (UCS), carbonate content, and mineralogy of the precipitates in the treated specimens were evaluated. The kinetics study showed that the rate of urea hydrolysis and the rate of precipitation for zero, five, and ten percent seawater were similar within the first 16 h of the reaction. After 16 h, it was observed that the rates dropped in the solution containing seawater, which might be attributed to the faster decay rate of urease enzyme when seawater is present. All the precipitates from the test tube experiments contained calcite and vaterite, with an increase in vaterite content by increasing the amount of seawater. The presence of ten percent seawater was found to not significantly affect the UCS, carbonate content, and mineralogy of the precipitates of the treated beach sand.

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The bio-mineralization of calcium carbonates is an innovative and eco-friendly technique for improving soil, which has recently become increasingly popular in the field of geotechnical engineering. Different bio-cementation methods are employed for improving granular soils, including microbially-induced CaCO3 precipitation (MICP) and enzymatic-induced carbonate precipitation (EICP). These methods offer innovativeness, effectiveness and sustainability when applied in geotechnical engineering, and have been suggested as possible solutions for various different geotechnical issues. More research has been conducted into MICP compared to EICP. Nevertheless, urease sourced from plants likely offers many benefits over the use of bacteria urease in bio-cementation processes. The present study reviews the mechanisms, possible areas for implementation, related benefits and drawbacks of the bio-cementations techniques. Additionally, it will concentrate on the techniques used in the precipitation of CaCO3 involving the urease hydrolysis of urea. The study findings will enhance the comprehension of biotechnical mechanisms and ensure that geotechnical specialists are suitably informed with up-to-date knowledge on this subject.

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