## 1 Introduction  
The mineralization of microorganisms is widespread in nature, and microbial-induced calcite precipitation (MICP) is a new biogeochemical soil improvement technology based on this idea [1; 2; 3; 4; 5; 6]. Because of its environmental friendliness and the availability of resources, it has been widely used in soil reinforcement [4; 7; 8], seepage control [9], anti-liquefaction [10], slope protection [11; 12], coastal erosion inhibition [13], fugitive dust prevention [14; 15], underground cultural relic repair, metal stability in contaminated soil [16], etc. However, due to the complex cultivation of high-producing urease microorganisms in MICP and the uncontrollability of enzyme activity, scholars are trying to induce calcium carbonate precipitation directly with enzyme-induced carbonate precipitation (EICP), especially urease [17; 18] that comes from plant seeds [19; 20] such as soybeans [21] and watermelon [22] seeds by means of the urea decomposition method [23; 24]. Compared to MICP, urease is the size of a nanometerand the solution is more water soluble, which makes EICP more suitable for fine soil. Free urease can be degraded to avoid negative impacts on the environment [8; 23].  
However, urease in EICP is in a free state and lacks nucleation sites provided by microbial macromolecules [7; 8; 9; 10; 11]. The formed calcium carbonate crystal structure is smaller, which is not conducive to the promotion of strength. The actual effect of soil reinforcement directly with urease is unsatisfactory [25]. To improve the reinforcement effect, many materials have been added to EICP, such as xanthan gum, guar gum, polymers, polyol-cellulose hydrogels [26; 27], biopolymers [28], chitosan [29], and milk [30; 31]. It was found that EICP with an appropriate amount of skim milk powder can enhance the unconfined compression strength (UCS) of soil by approximately 10 times [30]. [PERSON] et al. [31] pointed out that the phosphate group in casein and the carboxyl group on the N-terminus of \(\beta\)-casein are both SerP-SerP-SerP-X-SerP sequences, and calcium ions combine with casein and are salted out, resulting in aggregated casein precipitation that can be used as a center for calcium carbonate nucleation. In addition, scholars analyzed the influence of soil type [32; 33; 34; 35], reaction environment [36; 37], and reinforcement method [38] on the reinforcement effect [39; 40; 41; 42] and established theoretical [43] or numerical models [44] to calculate the calcium carbonate precipitation mass during EICP reinforcement.  
In this paper, to increase the efficiency of calcium carbonate production during the EICP process and expand its applicable soil type, an improved EICP was produced by adding organic material such as glutinous rice powder, brown sugar, and skim milk powder as a reinforcement for silt in the Yellow River flood area--referred to as China hereafter. A comparative study between silt columns using the improved EICP, traditional EICP, the addition of organic material only, and original untreated soil was conducted to verify the effectiveness of the improved EICP. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) results were examined to reveal the microscopic mechanics of the improved EICP proposed in this paper.