Calcium carbonate represents a large portion of carbon reservoir and is used commercially for a variety of applications. Microbial carbonate precipitation (MCP), a by-product of microbial activities, plays an important metal coprecipitation and cementation role in natural systems. This natural process occurring in various geological settings can be mimicked and used for a number of biotechnology such as metal remediation, carbon sequestration, enhanced oil recovery and construction restoration. In this study, different metabolic activities leading to calcium carbonate precipitation, their native environment, and potential applications and challenges are reviewed.

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Carbonate Precipitation through Microbial Activities in Natural Environment, and Their Potential in Biotechnology: A Review

The global magnitude (Pg) of soil organic carbon (SOC) is 677 to 0.3-m, 993 to 0.5-m, and 1,505 to 1-m depth. Thus, ~55% of SOC to 1-m lies below 0.3-m depth. Soils of agroecosystems are depleted of their SOC stock and have a low use efficiency of inputs of agronomic yield. This review is a collation and synthesis of articles published in peer-reviewed journals. The rates of SOC sequestration are scaled up to the global level by linear extrapolation. Soil C sink capacity depends on depth, clay content and mineralogy, plant available water holding capacity, nutrient reserves, landscape position, and the antecedent SOC stock. Estimates of the historic depletion of SOC in world soils, 115-154 (average of 135) Pg C and equivalent to the technical potential or the maximum soil C sink capacity, need to be improved. A positive soil C budget is created by increasing the input of biomass-C to exceed the SOC losses by erosion and mineralization. The global hotspots of SOC sequestration, soils which are farther from C saturation, include eroded, degraded, desertified, and depleted soils. Ecosystems where SOC sequestration is feasible include 4,900 Mha of agricultural land including 332 Mha equipped for irrigation, 400 Mha of urban lands, and ~2,000 Mha of degraded lands. The rate of SOC sequestration (Mg C ha-1  year-1 ) is 0.25-1.0 in croplands, 0.10-0.175 in pastures, 0.5-1.0 in permanent crops and urban lands, 0.3-0.7 in salt-affected and chemically degraded soils, 0.2-0.5 in physically degraded and prone to water erosion, and 0.05-0.2 for those susceptible to wind erosion. Global technical potential of SOC sequestration is 1.45-3.44 Pg C/year (2.45 Pg C/year).

Digging deeper: A holistic perspective of factors affecting soil organic carbon sequestration in agroecosystems.

Biocementation is a recently developed new branch in geotechnical engineering that deals with the application of microbiological activity to improve the engineering properties of soils. One of the most commonly adopted processes to achieve soil biocementation is through microbially induced calcite precipitation (MICP). This technique utilizes the metabolic pathways of bacteria to form calcite (CaCO3) that binds the soil particles together, leading to increased soil strength and stiffness. This paper presents a review of the use of MICP for soil improvement and discusses the treatment process including the primary components involved and major affecting factors. Envisioned applications, potential advantages and limitations of MICP for soil improvement are also presented and discussed. Finally, the primary challenges that lay ahead for the future research (i.e. treatment optimization, upscaling for in situ implementation and self-healing of biotreated soils) are briefly discussed.

State-of-the-Art Review of Biocementation by Microbially Induced Calcite Precipitation (MICP) for Soil Stabilization

Microbial induced calcite precipitation (MICP) is a novel biomediated ground improvement method that can be used to increase the shear strength and stiffness of soil. The evolution of the shear strength and stiffness of sand subjected to undrained and drained shearing is evaluated using triaxial tests. MICP treated sands with cementation levels ranging from young, uncemented sand to a highly cemented sandstonelike condition are subjected to undrained shear. A transition from strain hardening to strain softening behavior and a corresponding transition of global to localized failure as cementation is increased is observed. Moderately cemented specimens are subjected to various stress paths, which result in a change to the shear strength and volumetric behavior. Shear wave velocity is used to nondestructively monitor the change in small-strain stiffness during shearing, which provides an indication of cementation degradation as a function of strain level. Because shear wave velocity is influenced by ...

Stress-Strain Behavior of Sands Cemented by Microbially Induced Calcite Precipitation

Studies of soil improvement by microbial-induced calcite precipitation (MICP) have focused primarily on fine sand. This paper explores the viability of the MICP technique for improving the engineering properties of a typical tropical residual soil. A species of Bacillus, B. megaterium, was used to trigger calcite precipitation. Four variables were considered in this study: the concentration of B. megaterium, the concentration of the cementation reagent, the treatment duration, and the flow pressure of the cementation reagent. The results show that the improvement in the engineering properties of the MICP-treated residual soils is comparable to those of treated fine sands. The preferable treatment conditions for the soil studied are B. megaterium concentration of 1×108 cfu/mL, cementation reagent concentration of 0.5 M, flow pressure of 1.1 bar of the cementation reagent, and treatment duration of 48 h. Using this combination of parameters, the obtained shear strength increase and hydraulic conduct...

Factors Affecting Improvement in Engineering Properties of Residual Soil through Microbial-Induced Calcite Precipitation

Consideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems. This is a new paradigm for many in geotechnical engineering. Realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification. This paper assesses the progress, opportunities, and challenges in this emerging field. Biomediated geochemical processes, which consist of a geochemical reaction regulated by subsurface microbiology, currently being explored include mineral precipitation, gas generation, biofilm formation and biopolymer generation. For each of these processes, subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals, organic matter, pore fluids, and gases that constitute soil. Geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radionuclides. Challenges in biomediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process, and education of engineers and researchers.

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X. Cheng

Papers

Biogeochemical processes and geotechnical applications: progress, opportunities and challenges