Phosphate-Induced Surface Roughening Suppresses Bacterial Transport in Coral Sand.

Precipitation and sealing characteristics of enzyme-induced calcium carbonate precipitation in silica sands with varying particle shapes

Reduction of Sandy Soil Erodibility Using Bacterial Enzyme–Induced Calcite Precipitation

Bacterial enzyme–induced calcite precipitation (BEICP) has emerged as a promising technique to enhance the shear strength and reduce the erodibility of coarse-grained soils. Traditionally, research has focused on microbial-induced calcite precipitation (MICP), where calcium carbonate is generated through the bacterial activity of Sporosarcina pasteurii , utilizing urease enzymes within bacterial cells. In contrast, BEICP utilizes urease enzymes in an aqueous, cell-free suspension. This study explores the innovative application of surface-applied BEICP via a spray method to mitigate soil surface erodibility and improve the shear strength of a mixture of 20 / 30 standard Ottawa sand and Iowa loess silt. The experimental results demonstrated that increasing the total protein concentration on the soil surface enhances the shear strength by over 50% due to calcite precipitation. Furthermore, the induced calcite precipitation reduces the erodibility of the silty-sand mixtures by up to 15% under surface water erosion conditions. The novel spray application of BEICP proved to be an effective soil stabilization method against water erosion, highlighting its potential for practical implementation in erosion-prone areas.

Dual Effects of Brown Algae Impurities on Coral Concrete: Sulfate Resistance Decay and Multiscale Predictive Modeling

In island construction, the application of coral aggregate concrete (CAC) is challenged by marine biological impurities, particularly brown algae, which impact material performance. This study systematically investigates the effects of brown algae content (0%–6%), water-to-cement ratio, and sulfate ion wet–dry cycles on CAC’s fluidity, air content, compressive/splitting/axial strengths, and sulfate ion diffusion behavior. Results showed that brown algae content ≤ 2 % has negligible effect on fluidity, but higher contents significantly reduce workability. All strength parameters decreased with increasing impurity content and water-to-cement ratio. Early-stage seawater-immersion curing enhanced strength, but prolonged exposure led to significant degradation. A proposed strength prediction model demonstrated strong correlation with experimental data ( R 2 > 0.94 ). Under sulfate cycles, CAC’s mass loss rate, relative dynamic elastic modulus, and compressive strength exhibit a nonmonotonic increase-then-decrease trend, and the damage layer thickness grows exponentially with cycle, impurity content, and water-to-cement ratio. Controlling brown algae ≤ 2 % and water-to-cement ratio ≤ 0.3 optimizes sulfate erosion resistance. Numerical simulations reveal an exponential relationship between erosion depth and cycle, with uneven sulfate ion accumulation in CAC’s porous structure, highlighting diffusion heterogeneity. These findings provide critical technical guidelines for deploying CAC in marine environments, balancing ecological sustainability and engineering durability.

Biomineralization Influences the Transport of Bacteria and Cell-Associated Nanoparticles in Saturated Porous Media.

Understanding bacterial transport and fate in porous media is critical for effective bioremediation and water quality management. Although bacteria mediate (trans)formation of diverse nanoparticles, how biomineralization affects cell mobility remains unclear. Here, association with different biogenic nanoparticles was found to enhance the transport of mineralized Shewanella oneidensis MR-1 cells in quartz sand columns by altering bacterial viability, surface potential or hydrophobicity. Moreover, silver nanoparticle (AgNPs) biomineralization augmented extracellular electron transfer, energy taxis and redox responsiveness of resultant AgNPs-mineralized cells but impeded their mobility in ferrihydrite- and birnessite-coated columns. While quinone electron shuttles increased cell deposition in mineral-coated columns by stimulating energy taxis, natural humic acids promoted cell breakthrough through electrosteric repulsion. Negative tactic response toward abiogenic AgNPs induced enhanced breakthrough and pronounced blocking effects in bare sand column. Concurrence of negative chemotaxis toward abiogenic AgNPs and positive energy taxis toward ferrihydrite facilitated the transport of pristine MR-1, but restrained that of AgNPs-mineralized cells. Enhanced AgNPs-mineralized cells retention in ferrihydrite-coated columns further enabled AgNPs immobilization via microbial transformation of ferrihydrite to magnetite. In contrast, cell-associated AgNPs retained in birnessite-coated columns could be remobilized as nanoparticles via bioreductive birnessite dissolution or as Ag+ via birnessite oxidation, increasing the risk of silver dissemination.

A Critical Review of Engineering Properties of Soil Treated with Microbially Induced Calcium Carbonate Precipitation (MICP)

Microbially induced calcium carbonate precipitation (MICP) is a process that leverages microbial metabolic activity to facilitate biochemical interactions with surrounding chemical compounds, resulting in the precipitation of calcium carbonate. This mineralization process enhances soil properties by filling pores, binding soil particles, and reducing permeability, resulting in a significant increase in soil strength and stability. MICP holds great potential for various geotechnical and environmental engineering applications, including mitigating soil liquefaction, stabilizing erosion-prone slopes, remediating contaminated soils, and controlling seepage in infrastructure such as dams and tunnels. This review paper provides a concise overview of the cementation mechanism involved in MICP and the urea hydrolysis process, based on recent research findings. Key factors in evaluating the engineering properties of MICP-treated soils include compressive strength, permeability, stiffness, durability, volumetric behavior, shear wave velocity, and microstructural characteristics. Future research directions are discussed to guide the further development of MICP technology, focusing on the cost-effective bacterial strains, improved treatment uniformity, and the durability of MICP-treated soils under combined erosion and leachate conditions.

Effects of particle size and shape on strength of EICP-treated sand