## 1 Introduction  
With the acceleration of the urbanization process in China, the environmental issues are becoming increasingly prominent, and heavy metal pollution caused by anthropogenic activities has become a focus point due to the tremendous hazard to the ecosystem [1, 2]. Once enriched in the human body through the food chain [3], heavy metals will do harm to the kidney, brain and other important organs [4], and will potentially increase carcinogenic risks [5]. Research on the remediation of heavy-metal-polluted groundwater, wastewater and surface water has received worldwide attention [6, 7]. The immobilization of heavy metals via microbially induced carbonate precipitation (MICP) is an environmental-friendly and energy-saving technique, and can provide a promising and alternative solution to heavy metal pollution issues, bringing new opportunity for the remediation of heavy-metal-polluted water and improvement of environmental qualities [2, 8]. MICP is essentially a kind of biomineralization, which widely exists in nature. Calcium carbonate crystals with excellent cementing capacity can rapidly precipitate and accumulate when providing specific microorganisms with a wealth of calcium ions and nitrogenous nutrients [9, 10, 11]. Microorganisms mediate carbonate precipitation through heterotrophic pathways such as ammonification, denitrification, methane oxidation, sulfate reduction and ureolysis [12, 13]. Among those microbial metabolic pathways, ureolytic bacteria, with the superiority of easy control, speedy reaction rate and efficient chemical conversion, has become the most popular bacterium in the field of MICP research [9, 14]. Ureolytic bacteria can secrete urease through the metabolism process, which can catalyze the hydrolysis of urea, and the pH of the surrounding solution can correspondingly increase, resulting in the generation of ammonium and carbonate ions [15; 16]. Calcium ions can be adsorbed on the cell wall surface of negatively charged bacterium. Calcium ions and carbonate ions can take the cell membrane as crystal nucleus to form calcium carbonate crystals, and also can simultaneously coppecific heaty metal ions to immobilize heavy metals [17; 18; 19; 20]. The urea hydrolysis reaction process catalyzed by urease can be expressed by Equations (1)-(5). In the process of MICP, heavy metal or metalloid ions can replace Ca\({}^{2+}\) to form coprecipitates, be adsorbed on calcite to form complexes, incorporate into the CaCO\({}_{3}\) lattice structure, or enter into crystal interstices or defects [2; 21]. \[\text{CO(NH}_{2})_{2}+\text{H}_{2}\text{O}\xrightarrow{\text{ urease}}\text{NH}_{2}\text{COOH}+\text{NH}_{3} \tag{1}\]  
\[\text{NH}_{2}\text{COOH}+\text{H}_{2}\text{O}\xrightarrow{\text{ spontaneous}}\text{NH}_{3}+\text{H}_{2}\text{CO}_{3} \tag{2}\]  
\[\text{2 NH}_{3}+\text{2H}_{2}\text{O}\leftrightarrow\text{2 NH}_{4}{}^{+}+2\text{ OH}^{-} \tag{3}\]  
\[\text{H}_{2}\text{CO}_{3}\leftrightarrow\text{HCO}_{3}{}^{-}+\text{H}^{+} \tag{4}\]  
\[\text{HCO}_{3}{}^{-}+\text{H}^{+}+2\text{OH}^{-}\leftrightarrow\text{CO}_{3}{ }^{2-}+2\text{H}_{2}\text{O} \tag{5}\]  
Many ureolytic bacteria have been confirmed to have the ability of immobilizing heavy metals by biomineralization. As an excellent urease producing bacterium, _Sporosarcina pasteurii_ (_S. pasteurii_) is widely studied in the fields of biomaterials [11; 22; 23; 24; 25], crack sealing [26; 27], sand and soil improvement [28; 29; 30; 31; 32; 33; 34], etc. In recent years, scholars devoted to environmental remediation have applied _S. pasteurii_ to curb heavy metal polluted water [8; 35; 36]. [PERSON] et al. [37] set up batch experimental systems and found that the solid sequestration of solution contaminants associated with this carbonate precipitation process was element-specific, the solid phase capture of strontium was highly effective and rapid, the uranyl capture was not effective and copper uptake was very poor. [PERSON] et al.