## 1 Introduction  
Effect of toxic heavy metals on the environment has become a serious concern to the entire world because of the intrusion of heavy metals in the ecosystem [1]. Heavy metals cannot be decomposed and extirpated from the ecosystem because of their stability and cause atrocious health issues to the aquatic and terrestrial life [2]. Further, soil pollution due to heavy metals has become a grave concern to be addressed [3] since it also poses threat to the food security of the world [4], and it is not just hazardous to living creatures but it is a worldwide environmental issue [5,6]. Activities like plating of metals, mining, textile production, dyeing, manufacturing of batteries etc. cause heavy metal pollution in the environment [7]. The scale to which the heavy metal pollution has increased makes it imperative to find for the remediation methods. Hence heavy metal remediation is achieved by different methods like ion exchange, electrodialysis, nanofiltration, flocculation, chemical precipitation, reverse osmosis, ultrafiltration, coagulation and floatation [8]. Mostly adopted method for heavy metal remediation is adsorption due to its flexibility in operation [9]. One of the methods of heavy metal remediation in the soils is immobilization by solidifying the soil by a binder, which reduces the activity and solubility of heavy metals and even improves the mechanical characteristics of soils [10,11]. Given the present scenario wherein the heavy metal contamination has become a grave concern to be addressed at the earliest, methods like soil washing, chemical precipitation, ion exchange, reverse osmosis, electrochemical treatment, oxidation are employed to reduce the adverse effects of heavy metals in polluted environments [12, 13, 14, 15]. remediation of heavy metals in fly ashes deposits is also an important issue to be addressed [16]. Use of ground improvement techniques like compaction, stone columns and mixing soil with stabilizers are applied only in undeveloped sites, whereas the soils on which structures already exist can be developed with novel soil improvement methods [17]. Soil modification by biological process, wherein precipitates of calcium carbonate/calcite (CaCO\({}_{3}\)) are formed in the soil is a promising technique in improving the strength characteristics, reducing permeability and compression behavior of soil [18,19]. EICP technique is a bio-inspired method developed for soil treatment using urease enzyme wherein hydrolysis of urea takes place leading to the CaCO\({}_{3}\) precipitation which binds the soil grains together [20, 21, 22, 23, 24, 25]. Calcite precipitated by urease can accommodate in the pores between the soil grains and cement them [18, 26, 27, 28]. CaCO\({}_{3}\) is considered effective in the treatment of contaminated waters and shows good removal efficiency for heavy metals [29] and it is also considered as major bio- mineralization material [30]. The dimension of enzyme particle is 12 nm approximately [31,32], this minute size is advantageous in developing biofilms and precipitation of CaCO\({}_{3}\) on the soil grains to avoid bio-clogging. This small size of the enzyme is an advantage over microbially induced calcite precipitation (MICP) [31, 33], whereas the size of bacteria ranges from 3 to 0.5 \(\upmu\)m [34]. Use of MICP technique in soil treatment needs special care to ensure proper precipitation of CaCO\({}_{3}\) like providing a proper environment to offer sufficient oxygen for activation of microbes in a deep soil and sometimes voids in soil happen to be smaller than the bacteria cells posing a hindrance to the MICP process, whereas EICP technique is not impacted by these hindrances [35] and MICP used for precipitation of CaCO\({}_{3}\) for soil improvement is a complex phenomenon involving inorganic-organic, abiotic-biological and liquid-solid interactions. Factors such as physiological parameters of bacteria, properties of geomaterials, bacterial concentration and cementing solution influence the efficiency and quality of bonding in MICP [36].