A mini review of enzyme-induced calcite precipitation (EICP) technique for eco-friendly bio-cement production

This paper has presented a mini review of previously published articles dealing with bio-cement production using enzyme-induced calcite precipitation (EICP) technique. EICP is a biological, sustainable, and natural way of producing calcite without the direct involvement of microorganisms from urea and calcium chloride using urease enzyme in water-based solution with minimum energy consumption and eco-friendly. Calcite is a renewable bio-material that acts as a binder to improve the mechanical properties of soils like strength, stiffness, and water permeability. EICP has many real applications such as fugitive duct control with low cost comparing with water application or pouring, self-healing cracked concretes, and upgrade or change the low-volume road surfaces that are difficult for road constructions. The crystal structure of finally produced calcium carbonate (CaCO3), calcite is affected by the source of calcium ion; the calcite produced from calcium chloride has a rhombohedral crystal structure. The urease enzyme used for EICP applications could be produced in a laboratory-scale from different plant species, bacteria, some yeasts, fungi, tissues of humans, and invertebrates. Nevertheless, urease enzyme produced from jack beans has showed urease enzyme activity around 2700-3500U/g, and the tendency to replace the urease enzyme found in the global market. All urease enzymes have 12-nm size, and this smaller size makes EICP preferable for all types of soil or sands including fine and silt sands.

State-of-the-art review of soil erosion control by MICP and EICP techniques: Problems, applications, and prospects

In recent years, the application of microbially induced calcite precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) techniques have been extensively studied to mitigate soil erosion, yielding substantial achievements in this regard. This paper presents a comprehensive review of the recent progress in erosion control by MICP and EICP techniques. To further discuss the effectiveness of erosion mitigation in-depth, the estimation methods and characterization of erosion resistance were initially compiled. Moreover, factors affecting the erosion resistance of MICP/EICP-treated soil were expounded, spanning from soil properties to treatment protocols and environmental conditions. The development of optimization and upscaling in erosion mitigation via MICP/EICP was also included in this review. In addition, this review discussed the limitations and correspondingly proposed prospective applications of erosion control via the MICP/EICP approach. The current review presents up-to-date information on the research activities for improving erosion resistance by MICP/EICP, aiming at providing insights for interdisciplinary researchers and guidance for promoting this method to further applications in erosion mitigation.

Experimental Study on Different Improvement Schemes of EICP-Lignin Solidified Silt

In practical engineering applications, silt is prone to liquefaction and quicksand. This paper mainly studies the improvement effects of urease, lignin and their mixture on the strength and liquefaction resistance of silt. Based on the results and phenomena of an unconfined compressive strength and dynamic triaxial test, the improvement effects of the compressive strength, deformation resistance and liquefaction resistance of silt under different improvement schemes are analyzed, and the optimal values of the cement or lignin when enzyme-induced calcium carbonate precipitation (EICP) technology, lignin alone or EICP and lignin are obtained. The results show that the optimum concentration of the constant temperature and humidity sample (referred to as the constant humidity sample) and the constant temperature immersion sample (referred to as the soaking sample) of urease in the unconfined compressive strength test is 1.0 mol/L, and the compressive strength of the soaking sample is 4.9 MPa, which is 1.56 times that of the constant humidity sample; the optimum addition ratio of the lignin-improved constant humidity sample is 3%, and its compressive strength is 2.07 Mpa; the optimum addition ratio of the samples immersed at constant temperature is 4%, and the compressive strength is 3.05 MPa; when urease combines with lignin to improve silt, 4% is the best lignin addition ratio, the compressive strength of the constant humidity sample reaches 1.57 Mpa and the compressive strength of the soaking sample reaches 3.75 MPa; in the dynamic triaxial multi-stage cyclic load test, all samples were cured at constant humidity sample, and in the urease modified silt scheme, 1.0 mol/L was the optimal cement concentration; in the scheme of improving silt with lignin, 3% is the optimal addition ratio; when 1.25 mol/L cementation solution plus urease crude extract is combined with different ratios of lignin in the experimental scheme, 3% is the best lignin addition ratio.

Optimization of calcium carbonate precipitation during alpha-amylase enzyme-induced calcite precipitation (EICP)

The sand production during oil and gas extraction poses a severe challenge to the oil and gas companies as it causes erosion of pipelines and valves, damages the pumps, and ultimately decreases production. There are several solutions implemented to contain sand production including chemical and mechanical means. In recent times, extensive work has been done in geotechnical engineering on the application of enzyme-induced calcite precipitation (EICP) techniques for consolidating and increasing the shear strength of sandy soil. In this technique, calcite is precipitated in the loose sand through enzymatic activity to provide stiffness and strength to the loose sand. In this research, we investigated the process of EICP using a new enzyme named alpha-amylase. Different parameters were investigated to get the maximum calcite precipitation. The investigated parameters include enzyme concentration, enzyme volume, calcium chloride (CaCl₂) concentration, temperature, the synergistic impact of magnesium chloride (MgCl₂) and CaCl₂, Xanthan Gum, and solution pH. The generated precipitate characteristics were evaluated using a variety of methods, including Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). It was observed that the pH, temperature, and concentrations of salts significantly impact the precipitation. The precipitation was observed to be enzyme concentration-dependent and increase with an increase in enzyme concentration as long as a high salt concentration was available. Adding more volume of enzyme brought a slight change in precipitation% due to excessive enzymes with little or no substrate available. The optimum precipitation (87%) was yielded at 12 pH and with 2.5 g/L of Xanthan Gum as a stabilizer at a temperature of 75°C. The synergistic effect of both CaCl₂ and MgCl₂ yielded the highest CaCO₃ precipitation (32.2%) at (0.6:0.4) molar ratio. The findings of this research exhibited the significant advantages and insights of alpha-amylase enzyme in EICP, enabling further investigation of two precipitation mechanisms (calcite precipitation and dolomite precipitation).

Advances in Enzyme Induced Carbonate Precipitation and Application to Soil Improvement: A Review

Climate change and global warming have prompted a notable shift towards sustainable geotechnics and construction materials within the geotechnical engineer’s community. Earthen construction materials, in particular, are considered sustainable due to their inherent characteristics of having low embodied and operational energies, fire resistance, and ease of recyclability. Despite these attributes, they have not been part of the mainstream construction due to their susceptibility to water-induced deterioration. Conventional soil improvement techniques are generally expensive, energy-intensive, and environmentally harmful. Recently, biostabilization has emerged as a sustainable alternative that can overcome some of the limitations of existing soil improvement methods. Enzyme-induced carbonate precipitation (EICP) is a particularly promising technique due to its ease of application and compatibility with different soil types. EICP exploits the urease enzyme as a catalyst to promote the hydrolysis of urea inside the pore water, which, in the presence of calcium ions, results in the precipitation of calcium carbonate. The purpose of this paper is to provide a state-of-the-art review of EICP stabilization, highlighting the potential application of this technique to field problems and identifying current research gaps. The paper discusses recent progress, focusing on the most important factors that govern the efficiency of the chemical reactions and the precipitation of a spatially homogenous carbonate phase. The paper also discusses other aspects of EICP stabilization, including the degree of ground improvement, the prediction of the pore structure of the treated soil by numerical simulations, and the remediation of potentially toxic EICP by-products.

Enhanced rainfall erosion durability of enzymatically induced carbonate precipitation for dust control

Globally, most cities are facing severe challenges caused by dust pollution. Recently, the significant dust control application potential of the environmentally friendly enzymatically induced carbonate precipitation (EICP) has been demonstrated. However, repeated rainfall erosion negatively affects the long-term durability of several EICP treated areas. This study applied EICP and added either polyvinyl acetate (PVAc) or polyethylene glycol (PEG) to the cementation solution. The results showed that both PVAc and PEG could improve the shear resistance and rainfall-erosion resistance of treated dust soils. However, for repeated rainfall erosion, the surface strength and calcium carbonate (CaCO₃) contents of samples still decreased to less than 250 kPa and 1.1%, respectively. Therefore, combined EICP-PVAc-PEG treatment was proposed and the rainfall-erosion durability of treated dust soils was further studied. With the EICP-PVAc-PEG treatment, the dust samples achieved better shear resistance, higher surface strength, and better repeated rainfall-erosion resistance. Considering cost, cementation effects, and the effects of repeated rainfalls, EICP-PVAc-PEG treatment with 50 g/L PVAc and 30 g/L PEG was most suitable for dust control. The combined EICP-PVAc-PEG treatment significantly suppressed the generation of dust and improved the rainfall-erosion durability.

Improvement and Soil Consistency of Sand-Clay Mixtures Treated with Enzymatic-Induced Carbonate Precipitation

Recently, microbially induced carbonate precipitation (MICP) has been studied as an alternative for the improvement of sand–clay mixtures. However, the cementing uniformity of MICP-treated sand–clay mixtures cannot be guaranteed. In this present study, enzymatic-induced carbonate precipitation (EICP) was used to deal with it. The ions used in kaolin clay was predicted to affect the production rate for calcium carbonate (CaCO₃), which was studied using the calcification test. The solidification test was conducted using two different methods (the premixing method and the diffusion method). The permeability, unconfined compressive strength and the content of CaCO₃ of treated samples were obtained to evaluate the solidification effect of the EICP method. Moreover, in EICP treatment, the particle aggregation decreased the liquid limit, but the addition of solution increased it. Therefore, there were contrary effects to the soil consistency. In this study, the two types of liquid limits of treated samples were measured with deionized water and 2M-NaCl brine, respectively. The results show that the Al₂O₃, NaCl and MgCl₂ in the kaolin clay had a slight impact on the production rate for CaCO₃, while FeCl₃ significantly inhibited it. The EICP method can improve sand–clay mixtures and decrease their permeability. Different from MICP, the EICP method can guarantee the uniformity of treated samples. Moreover, the liquid limit of the sample treated with the premixing method decreased, while that of the sample treated with the diffusion method increased firstly and then decreased with the increasing treatment cycles. Different from the deionized water, the pore-fluid chemistry had a larger effect on the liquid limit with 2M-NaCl brine.