# Recent Developments on Biomineralization for Erosion Control
## 2 Biomineralization Process and Efficiency Optimization  
### Traditional Biomineralization Process  
The traditional biomineralization process, particularly MICP, leverages the metabolic activity of ureolytic bacteria, most notably _Sporosarcina pasteurii_, to precipitate calcium carbonate (CaCO\({}_{3}\)) in porous media [111]. This process involves two critical biochemical reactions:  
(1) Ureolysis: _Sporosarcina pasteurii_ hydrolyzes urea into ammonium (NH\({}_{4}\)\({}^{+}\)) and carbonate ions (CO\({}_{3}\)\({}^{2-}\)) via the enzyme urease:  
\[\mathrm{CO(NH_{2})}_{2}+2\mathrm{H_{2}O}\stackrel{{ bacteria}}{{ \rightarrow}}2\mathrm{NH_{4}^{+}}+\mathrm{CO_{3}^{2-}} \tag{1}\](2) Calcium carbonate precipitation: The generated CO\({}_{3}\)\({}^{2-}\) reacts with free calcium ions (Ca\({}^{2+}\)) to form calcium carbonate:  
\[\text{CO}_{3}^{2-}+\text{Ca}^{2+}\rightarrow\text{CaCO}_{3}\downarrow \tag{2}\]  
These reactions occur optimally at pH 7-9, driven by bacterial mineralization capacity and site-specific geochemical conditions. The CaCO\({}_{3}\) crystals nucleate heterogeneously on microbial cell walls or sediment particles, progressively cementing soil grains and filling pore spaces [112]. [PERSON] (2004) found that the optimal pH value for urease activity in bacterial solution containing bacterial cells is 9. pH controls the deposition rate, yield, and morphology of calcium carbonate by affecting the concentration of ammonium, carbonate, and bicarbonate ions in the porous medium solution. When the supersaturated concentration of the reaction ions (calcium ions and carbonate ions) is higher, the formation rate of calcium carbonate is faster and the crystals are smaller [51]. Studies have shown that there is an optimal pH range [113; 114]. With the increase in pH, urease activity first increases and then decreases. Generally, calcium carbonate content and uniaxial compressive strength also show a trend of first increasing and then decreasing. However, compressive strength is related to factors such as ambient temperature, sand type, and pore distribution. The exact change in strength cannot be strictly determined based on the change of a single pH value.  
The efficiency of biomineralization hinges on microbial metabolic activity, substrate availability, and environmental adaptability. Urease activity directly correlates with reaction kinetics. For instance, _Sporosarcina pasteuri_ (_S. p._) exhibits urease activity with a \(V_{\text{max}}\) of 3.55 mM urea hydrolyzed min\({}^{-1}\cdot\)mg\({}^{-1}\) at pH 7.0 and 25 \({}^{\circ}\)C under optimal aerobic conditions, demonstrating significantly faster microbiological CaCO\({}_{3}\) precipitation compared to chemical processes. While _S. p._ is capable of ureolysis under both aerobic and anaerobic conditions, the presence of oxygen enhances bacterial growth and enzyme expression, thereby improving biomineralization efficiency [115]. At present, a large number of calcium carbonate sediments have been found in the ocean environment, from coastlines to seabed sediments; they generally come from organic life forms such as corals and show obvious biological characteristics [49; 116]. They interact with the complex ocean environment through the mineralization of urease-producing microorganisms in the coastlines and seabed and eventually precipitation. This type of sediment preserves good strength characteristics and porosity, providing an excellent shelter for the survival of organisms on coastlines and the seabed. However, it should be noted that under natural conditions, the formation of carbonate precipitation generally takes a long time, which mainly depends on the urease activity of bacteria, reactant concentration, temperature, humidity, oxygen, and other conditions. Especially in the ocean environment, how to intensify the process of biomineralization through artificial intervention and form technology that is beneficial to us is a question worth considering. In addition, the bacterial survival in seawater is also a limitation that hinders application.