Flume study on the effects of microbial induced calcium carbonate precipitation (MICP) on the erosional behaviour of fine sand

Tangential flow-induced interface erosion poses a major threat to a wide variety of engineering structures, such as earth-filled embankment dams, and oil- and gas-producing wells. This study explores the applicability of microbial induced calcium carbonate (CaCO3) precipitation (MICP) by way of the ureolytic soil bacterium Sporosarcina pasteurii as a method for enhancing the surface erosion resistance of fine sand. Specimens were treated with cementation solution concentrations between 0·02 and 0·1 M, and the erosional behaviour examined in a flume under surface-parallel flow and increasing shear stress. Photographs, cumulative height eroded-time series and erosion rates were obtained as a function of specimen height, MICP treatment formulation and calcium carbonate content. Results showed that while untreated specimens eroded primarily in particulate and mass form, MICP-treated specimens were characterised by a block erosion mechanism. Further, erodibility was found to depend on the calcium carbonate content and the cementation solution concentration. To understand this, a systematic study of the calcium carbonate crystal sizes and distributions was undertaken through X-ray computed tomography. Fundamentally, the effectiveness of MICP for erosion control was found to be dominated both by the precipitated calcium carbonate content and microstructural features, with higher contents and larger crystals yielding lower erodibility values. Additionally, crystal growth mechanisms varied depending on the cementation solution concentration.</p

Characterisation of CaCO3 phases during strain-specific ureolytic precipitation

Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, however, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. We have studied microbial induced calcium carbonate (CaCO3) precipitation (MICP) in three ureolytic bacterial strains from the Sporosarcina family, including S. newyorkensis, a newly isolated microbe from the deep sea. We find that the interplay between structural water and strain-specific amino acid groups is fundamental to the stabilisation of vaterite and that, under the same conditions, different isolates yield distinctly different polymorphs. The latter is found to be associated with different urease activities and, consequently, precipitation kinetics, which change depending on pressure-temperature conditions. Further, CaCO3 polymorph selection also depends on the coupled effect of chemical treatment and initial bacterial concentrations. Our findings provide new insights into strain-specific CaCO3 polymorphic selection and stabilisation, and open up promising avenues for designing bio-reinforced geo-materials that capitalise on the different particle bond mechanical properties offered by different polymorphs

Effect of Bacterial Strain on MICP and its Application for the Erosion Control of Fine Sands

Tangential flow-induced erosion poses a major threat to a wide variety of engineering structures, including earth-filled embankment dams and oil and gas extraction wells. Current mitigation solutions are limited to mechanical approaches (e.g. filters, gravel packs), relying on the fulfilment of a ‘paradoxical permeability-retention criterion’; and to the use of emergency hydraulic head reduction which limits serviceability. In this context, microbial induced calcium carbonate (CaCO3) precipitation (MICP) could be used to enhance the erosion performance of soils. This research investigates the influence of the CaCO3 microstructure on the macromechanical erosion response of fine sands by combining instrumental techniques for characterisation, with element-scale flume testing and controlled modelling of a heterogeneous layered system. The flume tests employed a newly designed Erosion Function Apparatus (EFA) and testing procedure to measure surface erosion, focusing on fine-coarse sand interfaces treated with the same soil bacterium (Sporosarcina pasteurii), but varying urea-CaCl2 solution concentrations. The key aspect examined was the role of CaCO3 micro-architecture – comprised of the CaCO3 vertical profile, crystal size and distribution, and morphology. Results showed that higher CaCO3contents, bigger crystals, and cohesive bonds yield lower erodibility values. It was also seen that crystal growth mechanisms could change depending on bacterial distributions, urea-CaCl2 solution concentrations, and the pore space of the original granular material. As MICP moves from research into practice, the effect of bacterial strain on CaCO3 precipitation also needs to be considered. The morphology, mineralogy and crystalline properties of biominerals precipitated by three different ureolytic microorganisms were henceforth investigated. These strains were: S. pasteurii, S. aquimarina, and S. newyorkensis – a newly isolated microbe from the Daini-Atsumi Knoll in offshore Japan. From in vitro experiments it was found that CaCO3 polymorph selection can be controlled through selection of ureolytic strain with appropriate precipitation kinetics, and that metastable polymorph stabilisation is dependent on the kinetics of the mobile water contained within the crystal structure. Finally, the Cambridge Plane-Strain Sand Production Apparatus (SPA), through the incorporation of Particle Image Velocimetry, was used to examine the effect of bacterial strain-specific MICP on the deformation mechanisms of a layered granular system resulting from lateral unloading due to erosion. It was observed that MICP treatment reduces sand production at the expense of ductility, however, this behaviour becomes more prominent with increasing CaCO3 polymorph stability – namely, amorphous calcium carbonate (ACC), vaterite, and calcite. Correlations between microstructual characterisation, and EFA and SPA results highlighted the potential for designing bio-reinforced geo-materials that capitalise on the different CaCO3 microstructural features.The author would like to acknowledge the EPSRC Centre for Doctoral Training in Future Infrastructure and Built Environment at the University of Cambridge (EPSRC grant reference number EP/L016095/1). In addition, this study was conducted as part of the activity of the Research Consortium for Methane Hydrate Resources in Japan [MH21 Research Consortium] as planned by the Ministry of Economy, Trade, and Industry (METI), Japan. Thank you to the crew of D/V Chikyu for the 2012 JOGMEC/JAPEX pressure coring operation. In addition, the author would like to acknowledge the additional financial support from the Cambridge Philosophical Society Research Studentship

Uncovering the dynamics of urease and carbonic anhydrase genes in ureolysis, carbon dioxide hydration and calcium carbonate precipitation

The hydration of CO2 suffers from kinetic inefficiencies that make its natural trapping impractically sluggish. However, CO2-fixing carbonic anhydrases remarkably accelerate its equilibration by six orders of magnitude and are, therefore, ’ideal’ catalysts. Notably, carbonic anhydrase has been detected in ureolytic bacteria, suggesting its potential involvement in microbial induced carbonate precipitation (MICP), yet the dynamics of the urease (Ur) and carbonic anhydrase (CA) genes remain poorly understood. Here, through the use of ureolytic bacterium Sporosaracina pasteurii, we investigate the differing role of Ur and CA in ureolysis, CO2 hydration, and CaCO3 precipitation with increasing CO2(g) concentrations. We show that Ur gene up-regulation coincides with an increase in [HCO3-] following the hydration of CO2 to HCO3- by CA. Hence, CA physiologically promotes buffering, which enhances solubility trapping and affects the phase of the CaCO3 mineral formed. Understanding the role of CO2 hydration on the performance of ureolysis and CaCO3 precipitation provides essential new insights, required for the development of next-generation bio-catalysed CO2 trapping technologies.Civil, Architectural, and Environmental Engineerin

Uncovering the Dynamics of Urease and Carbonic Anhydrase Genes in Ureolysis, Carbon Dioxide Hydration, and Calcium Carbonate Precipitation.

The hydration of CO2 suffers from kinetic inefficiencies that make its natural trapping impractically sluggish. However, CO2-fixing carbonic anhydrases (CAs) remarkably accelerate its equilibration by 6 orders of magnitude and are, therefore, "ideal" catalysts. Notably, CA has been detected in ureolytic bacteria, suggesting its potential involvement in microbially induced carbonate precipitation (MICP), yet the dynamics of the urease (Ur) and CA genes remain poorly understood. Here, through the use of the ureolytic bacteriumSporosarcina pasteurii, we investigate the differing role of Ur and CA in ureolysis, CO2 hydration, and CaCO3 precipitation with increasing CO2(g) concentrations. We show that Ur gene up-regulation coincides with an increase in [HCO3-] following the hydration of CO2 to HCO3- by CA. Hence, CA physiologically promotes buffering, which enhances solubility trapping and affects the phase of the CaCO3 mineral formed. Understanding the role of CO2 hydration on the performance of ureolysis and CaCO3 precipitation provides essential new insights, required for the development of next-generation biocatalyzed CO2 trapping technologies

Microbially induced carbonate precipitation (MICP) for soil strengthening: A comprehensive review

Geotechnical research has been yearning for revolutionary innovations that could bring breakthroughs to conventional practices, especially at a time when energy efficiency and environmental sustainability are of unprecedented importance in the field. Recently, exciting opportunities emerged utilising microorganisms, the ubiquitous soil dwellers, to provide solutions to many geotechnical problems, prompting the development of the new, multidisciplinary subject of biogeotechnics. Research interest has been centred on the use of microbially induced carbonate precipitation (MICP) to improve the engineering properties of soils. The present work aims to comprehensively review the progress of more than a decade of research on the application of MICP in soil strengthening. Through elucidation of underlying mechanisms, compilation and interpretation of experimental findings, and in-depth discussion on pivotal aspects, with reference made to key published studies, a holistic picture of the state of the art of MICP-based soil strengthening is drawn. Current knowledge gaps are identified, and suggestions for future research are given, along with the opportunities and challenges that lie ahead of practically implementing this technique in real-world geotechnical applications.EPSRC EP/S02302X/

Controlling the calcium carbonate microstructure of engineered living building materials.

The fabrication of responsive soft materials that enable the controlled release of microbial induced calcium carbonate (CaCO3) precipitation (MICP) would be highly desirable for the creation of living materials that can be used, for example, as self-healing construction materials. To obtain a tight control over the mechanical properties of these materials, needed for civil engineering applications, the amount, location, and structure of the forming minerals must be precisely tuned; this requires good control over the dynamic functionality of bacteria. Despite recent advances in the self-healing of concrete cracks and the understanding of the role of synthesis conditions on the CaCO3 polymorphic regulation, the degree of control over the CaCO3 remains insufficient to meet these requirements. We demonstrate that the amount and location of CaCO3 produced within a matrix, can be controlled through the concentration and location of bacteria; these parameters can be precisely tuned if bacteria are encapsulated, as we demonstrate with the soil-dwelling bacterium Sporosarcina pasteurii that is deposited within biocompatible alginate and carboxymethyl cellulose (CMC) hydrogels. Using a competitive ligand exchange mechanism that relies on the presence of yeast extract, we control the timing of the release of calcium ions that crosslink the alginate or CMC without compromising bacterial viability. With this novel use of hydrogel encapsulation of bacteria for on-demand release of MICP, we achieve control over the amount and structure of CaCO3-based composites and demonstrate that S. pasteurii can be stored for up to 3 months at an accessible storage temperature of 4 °C, which are two important factors that currently limit the applicability of MICP for the reinforcement of construction materials. These composites thus have the potential to sense, respond, and heal without the need for external intervention

Characterisation of CaCO 3 phases during strain-specific ureolytic precipitation

Abstract: Numerous microbial species can selectively precipitate mineral carbonates with enhanced mechanical properties, however, understanding exactly how they achieve this control represents a major challenge in the field of biomineralisation. We have studied microbial induced calcium carbonate (CaCO3) precipitation (MICP) in three ureolytic bacterial strains from the Sporosarcina family, including S. newyorkensis, a newly isolated microbe from the deep sea. We find that the interplay between structural water and strain-specific amino acid groups is fundamental to the stabilisation of vaterite and that, under the same conditions, different isolates yield distinctly different polymorphs. The latter is found to be associated with different urease activities and, consequently, precipitation kinetics, which change depending on pressure-temperature conditions. Further, CaCO3 polymorph selection also depends on the coupled effect of chemical treatment and initial bacterial concentrations. Our findings provide new insights into strain-specific CaCO3 polymorphic selection and stabilisation, and open up promising avenues for designing bio-reinforced geo-materials that capitalise on the different particle bond mechanical properties offered by different polymorphs