Microbial Geotechnology is a new branch of geotechnical engineering that deals with the applications of microbiological methods to geological materials used in engineering. The aim of these applications is to improve the mechanical properties of soil so that it will be more suitable for construction or environmental purposes. Two notable applications, bioclogging and biocementation, have been explored. Bioclogging is the production of pore-filling materials through microbial means so that the porosity and hydraulic conductivity of soil can be reduced. Biocementation is the generation of particle-binding materials through microbial processes in situ so that the shear strength of soil can be increased. The most suitable microorganisms for soil bioclogging or biocementation are facultative anaerobic and microaerophilic bacteria, although anaerobic fermenting bacteria, anaerobic respiring bacteria, and obligate aerobic bacteria may also be suitable to be used in geotechnical engineering. The majority of the studies on Microbial Geotechnology at present are at the laboratory stage. Due to the complexity, the applications of Microbial Geotechnology would require an integration of microbiology, ecology, geochemistry, and geotechnical engineering knowledge.

Applications of microorganisms to geotechnical engineering for bioclogging and biocementation of soil in situ

Microbiological deterioration and degradation of synthetic polymeric materials: recent research advances

Phytoremediation of highly water soluble and volatile organic xenobiotics is often inefficient because plants do not completely degrade these compounds through their rhizospheres. This results in phytotoxicity and/or volatilization of chemicals through the leaves, which can cause additional environmental problems. We demonstrate that endophytic bacteria equipped with the appropriate degradation pathway improve the in planta degradation of toluene. We introduced the pTOM toluene-degradation plasmid of Burkholderia cepacia G4 into B. cepacia L.S.2.4, a natural endophyte of yellow lupine. After surface-sterilized lupine seeds were successfully inoculated with the recombinant strain, the engineered endophytic bacteria strongly degraded toluene, resulting in a marked decrease in its phytotoxicity, and a 50–70% reduction of its evapotranspiration through the leaves. This strategy promises to improve the efficiency of phytoremediating volatile organic contaminants.

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Engineered endophytic bacteria improve phytoremediation of water-soluble, volatile, organic pollutants

Phosphorus (P) is a critical, geographically concentrated, nonrenewable resource necessary to support global food production. In excess (e.g., due to runoff or wastewater discharges), P is also a primary cause of eutrophication. To reconcile the simultaneous shortage and overabundance of P, lost P flows must be recovered and reused, alongside improvements in P-use efficiency. While this motivation is increasingly being recognized, little P recovery is practiced today, as recovered P generally cannot compete with the relatively low cost of mined P. Therefore, P is often captured to prevent its release into the environment without beneficial recovery and reuse. However, additional incentives for P recovery emerge when accounting for the total value of P recovery. This article provides a comprehensive overview of the range of benefits of recovering P from waste streams, i.e., the total value of recovering P. This approach accounts for P products, as well as other assets that are associated with P and can be recovered in parallel, such as energy, nitrogen, metals and minerals, and water. Additionally, P recovery provides valuable services to society and the environment by protecting and improving environmental quality, enhancing efficiency of waste treatment facilities, and improving food security and social equity. The needs to make P recovery a reality are also discussed, including business models, bottlenecks, and policy and education strategies.

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Total Value of Phosphorus Recovery

In vitro and in vivo model systems to study microbial biofilm formation

An engineered microbial biofilm barrier capable of reducing aquifer hydraulic conductivity while simultaneously biodegrading nitrate has been developed and tested at a field-relevant scale. The 22-month demonstration project was conducted at the MSE Technology Applications Inc. test facility in Butte, Montana, which consisted of a 130 ft wide, 180 ft long, 21 ft deep, polyvinylchloride (PVC)-lined test cell, with an initial hydraulic conductivity of 4.2 × 10−2 cm/s. A flow field was established across the test cell by injecting water upgradient while simultaneously pumping from an effluent well located approximately 82 ft down gradient. A 30 ft wide biofilm barrier was developed along the centerline of the test cell by injecting a starved bacterial inoculum of Pseudomonas fluorescens strain CPC211a, followed by injection of a growth nutrient mixture composed of molasses, nitrate, and other additives. A 99% reduction of average hydraulic conductivity across the barrier was accomplished after three months o...

Subsurface biofilm barriers for the containment and remediation of contaminated groundwater

Observation of thick biofilm accumulation and structure in porous media and corresponding hydrodynamic and mass transfer effects

Effects of starvation on bacterial transport through porous media

Dual-species microbial interactions have been extensively reported for batch and continuous culture environments. However, little research has been performed on dual-species interaction in a biofilm. This research examined the effects of growth rate and substrate concentration on dual-species population densities in batch and biofilm reactors. In addition, the feasibility of using batch reactor kinetics to describe dual-species biofilm interactions was explored. The scope of the research was directed toward creating a dual-species biofilm for the biodegradation of trichloroethylene, but the findings are a significant contribution to the study of dual-species interactions in general. The two bacterial species used were Burkholderia cepacia PR1-pTOM31c, an aerobic organism capable of constitutively mineralizing trichloroethylene (TCE), and Klebsiella oxytoca, a highly mucoid, facultative anaerobic organism. The substrate concentrations used were different dilutions of a nutrient-rich medium resulting in dissolved organic carbon (DOC) concentrations on the order of 30, 70, and 700 mg/L. Presented herein are single- and dual-species population densities and growth rates for these two organisms grown in batch and continuous-flow biofilm reactors. In batch reactors, planktonic growth rates predicted dual-species planktonic species dominance, with the faster-growing organism (K. oxytoca) outcompeting the slower-growing organism (B. cepacia). In a dual-species biofilm, however, dual-species planktonic growth rates did not predict which organism would have the higher dual-species biofilm population density. The relative fraction of each organism in a dual-species biofilm did correlate with substrate concentration, with B. cepacia having a greater proportional density in the dual-species culture with K. oxytoca at low (30 and 70 mg/L DOC) substrate concentrations and K. oxytoca having a greater dual-species population density at a high (700 mg/L DOC) substrate concentration. Results from this research demonstrate the effectiveness of using substrate concentration to control population density in this dual-species biofilm.

Interaction of Klebsiella oxytoca and Burkholderia cepacia in Dual-Species Batch Cultures and Biofilms as a Function of Growth Rate and Substrate Concentration

Robert Sharp

Papers

Subsurface biofilm barriers for the containment and remediation of contaminated groundwater

Observation of thick biofilm accumulation and structure in porous media and corresponding hydrodynamic and mass transfer effects

Effects of starvation on bacterial transport through porous media

Interaction of Klebsiella oxytoca and Burkholderia cepacia in Dual-Species Batch Cultures and Biofilms as a Function of Growth Rate and Substrate Concentration

Visualization and characterization of dynamic patterns of flow, growth and activity of biofilms growing in porous media