Microbial and Geochemical Dynamics of an Aquifer Stimulated for Microbial Induced Calcite Precipitation (MICP)

Abstract

Microbially induced calcite precipitation (MICP) is an alternative to existing soil stabilization techniques for construction and erosion. As with any biologically induced process in soils or aquifers, it is important to track changes in the microbial communities that occur as a result of the treatment. Our research assessed how native microbial communities developed in response to injections of reactants (dilute molasses as a carbon source; urea as a source of nitrogen and alkalinity) that promoted MICP in a shallow aquifer. Microbial community composition (16S rRNA gene) and ureolytic potential (ureC gene copy numbers) were also measured in groundwater and artificial sediment. Aquifer geochemistry showed evidence of sulfate reduction, nitrification, denitrification, ureolysis, and iron reduction during the treatment. The observed changes in geochemistry corresponded to microbial community succession in the groundwater and this matched parallel geophysical and mineralogical evidence of calcite precipitation in the aquifer. We detected an increase in the number of ureC genes in the microbial communities at the end of the injection period, suggesting an increase in the abundance of microbes possessing this gene as needed to hydrolyze urea and stimulate MICP. We identify geochemical and biological markers that highlight the microbial community response that can be used along with geophysical and geotechnical evidence to assess progress of MICP.

Native Bacterial Community Convergence in Augmented and Stimulated Ureolytic MICP Biocementation

“…That approach lacks the selective pressure inherent to the dynamic chemical conditions and repeated washout–regrowth cycles employed here and expected during in situ stimulation field applications. A recent field study, in which an aquifer was stimulated with dilute urea (8–64 mM) and molasses (0.13–1.11 g L −1 as a carbon and energy source), showed little evidence that ureolytic bacterial populations were enriched to the extent required to precipitate native divalent cations as carbonates . Despite observed increases in ureC copy number, no measurements of urea or ureolytic activity were presented, nor were notable cations or carbonate content directly quantified.…”

“…A recent field study, in which an aquifer was stimulated with dilute urea (8−64 mM) and molasses (0.13− 1.11 g L −1 as a carbon and energy source), showed little evidence that ureolytic bacterial populations were enriched to the extent required to precipitate native divalent cations as carbonates. 42 Despite observed increases in ureC copy number, no measurements of urea or ureolytic activity were presented, nor were notable cations or carbonate content directly quantified. Additionally, the stimulated suspended communities bear little resemblance to those seen here or elsewhere, with only one transient appearance of substantial Firmicutes in a single sample (29%), the rest being composed primarily of Proteobacteria with minute Firmicute abundance.…”

“…pasteurii over the course of cementation treatments and the relative performances of the two methods, judged by bulk ureolytic rates and extent of biomineralization. Although recent research has begun to characterize the microbial communities enriched by stimulated MICP, − these studies do not reproduce potentially important conditions of in situ stimulation as discussed below. Understanding the poorly characterized microbiology supporting these systems in conditions closely analogous to field implementations will allow for the development of informed optimization strategies capable of furthering the competitive advantages of MICP over traditional soil improvement methods.…”

Critical Review of Solidification of Sandy Soil by Microbially Induced Carbonate Precipitation (MICP)

“…Due to the complexity of the natural environment, some phenomena are difficult to explain. Ohan et al [106] found that after applying MICP, the pH value of groundwater decreased, which contradicted the normal pH value increase.…”

Effect of Glutinous Rice Slurry on the Reinforcement of Silt in the Yellow River Basin by Microbially Induced Carbonate Precipitation (MICP): Mechanical Property and Microcosmic Structure

“…e influence of the concentration of Ca 2+ and reaction time on the morphology and polymorph of CaCO 3 crystals was researched to reveal the mechanism of MICP [26]. e combination of glutinous rice slurry and calcium carbonate can further strengthen the mechanical properties of soil [27][28][29][30].…”