## 1 Introduction
It is understood that ensuring a consistent distribution of calcite in the MICP process is vital for its successful application in various fields, and these experimental and numerical methods contribute to better uniformity and mechanical properties of the treated soil, making MICP a more effective option for soil enhancement. Nonetheless, while field trials have demonstrated the viability of various bio-based methods such as bio-gelation, bio-clogging, biogas desaturation, and bio-cementation, challenges still exist, such as inhomogeneity, and an effective injection strategy is crucial to ensuring the substrates are delivered properly, promoting a uniform distribution of precipitated calcium carbonate [22]. Hydrophobic gel-like biopolymers such as polyhydroxybutyrate, xanthan, chitosan, and polyglutamic acid are also used for soil improvement [23]. In recent years, studies have been conducted in the literature using biopolymer additives to increase the effectiveness of MICP. For instance, [PERSON] et al. [24] examined the role of a chitosan biopolymer in influencing the MICP process and observed that it facilitates nucleation and modulates the growth of MnCO\({}_{3}\). This is achieved by providing nucleation sites for mineral formation and mitigating the toxic effects of metal ions. Their findings suggest that chitosan holds promise for enhancing the efficiency and sustainability of the MICP process. In another study, [PERSON] et al. [25] investigated the impact of adding xanthan gum biopolymer to enhance the reinforcement effect of MICP in sandy soils. They found that incorporating 2 g/L xanthan gum into the bio-cementation process significantly enhanced the strength and structural integrity of sandy soil samples more than those treated with either MICP or xanthan gum alone. In addition, naturally occurring organic substances, such as polysaccharides, may play a role in controlling the polymorphism and morphology of MICP [26]. SA, a biosynthetic polysaccharide, can simulate the impact of polysaccharides on CaCO\({}_{3}\) formation, offering several advantages in this process: The calcium alginate gel provides a habitat for microorganisms, gradually releasing calcium for in situ precipitation, while alginate molecules affect the CaCO\({}_{3}\) morphology through gel collapse, with the negative charges on the alginate molecules significantly affecting the polymorphism and morphology of CaCO\({}_{3}\), as observed with varying concentrations of SA [26]. When considering the unique contribution of sodium alginate (SA) to MICP efficiency in comparison to other biopolymers, SA stands out due to its strong gel-forming ability, effective calcium ion binding capacity, and superior performance in reducing soil permeability. According to the literature, SA has been shown to reduce permeability by approximately 20 times more than biopolymers such as guar gum [27]. Additionally, SA supports the sustained activity of MICP by supplying oxygen and nutrients to bacteria, enhances the injectability of the cementing solution, and contributes to more homogeneous calcite precipitation [28]. For these reasons, the SA + MICP combination fills an important gap in the literature and offers an original solution for simultaneously improving both soil strength and hydraulic conductivity. It is understood that studies in the literature highlight the importance of ensuring homogeneous distribution, and while experimental and analytical approaches have been proposed, they remain limited in number; additionally, biopolymer additives have proven to be a highly effective factor in CaCO\({}_{3}\) formation. In addition, the method of applying the bacteria-cementitious solution into the soil affects the homogeneity of the treated solution, which in turn determines the success of the method, with three possible introduction techniques: injection, surface percolation, and pre-mixing [29].