Permeability of a growing biofilm in a porous media fluid flow analyzed by magnetic resonance displacement-relaxation correlations.

Biofilm growth in porous media is difficult to study non-invasively due to the opaqueness and heterogeneity of the systems. Magnetic resonance is utilized to non-invasively study water dynamics within porous media. Displacement-relaxation correlation experiments were performed on fluid flow during biofilm growth in a model porous media of mono-dispersed polystyrene beads. The spin-spin T2 magnetic relaxation distinguishes between the biofilm phase and bulk fluid phase due to water-biopolymer interactions present in the biofilm, and the flow dynamics are measured using PGSE NMR experiments. By correlating these two measurements, the effects of biofilm growth on the fluid dynamics can be separated into a detailed analysis of both the biofilm phase and the fluid phase simultaneously within the same experiment. Within the displacement resolution of these experiments, no convective flow was measured through the biomass. An increased amount of longitudinal hydrodynamic dispersion indicates increased hydrodynamic mixing due to fluid channeling caused by biofilm growth. The effect of different biofilm growth conditions was measured by varying the strength of the bacterial growth medium.

Biofilm detection in natural unconsolidated porous media using a low-field magnetic resonance system.

The extent to which T(2) relaxation measurements can be used to determine biofouling in several natural geological sand media using a low-field (275 kHz, 6.5 mT) NMR system has been demonstrated. It has been previously shown that, at high laboratory strength fields (300 MHz, 7 T), T(2) techniques can be used as a bioassay to confirm the growth of biofilm inside opaque porous media with low magnetic susceptibilities such as borosilicate or soda lime glass beads. Additionally decreases in T(2) can be associated with intact biofilm as opposed to degraded biofilm material. However, in natural geological media, the strong susceptibility gradients generated at high fields dominated the T(2) relaxation time distributions and biofilm growth could not be reliably detected. Samples studied included Bacillus mojavensis biofilm in several sand types, as well as alginate solution and alginate gel in several sand types. One of the sand types was highly magnetic. Data was collected with a low-field (275 kHz, 6.5 mT) benchtop NMR system using a CPMG sequence with an echo time of 1.25 ms providing the ability to detect signals with T(2) greater than 1 ms. Data presented here clearly demonstrate that biofilm can be reliably detected and monitored in highly magnetically susceptible geological samples using a low-field NMR spectrometer indicating that low-field NMR could be viable as a biofilm sensor at bioremedation sites.

Monitoring residual fouling after cleaning of multi-fiber membrane modules fiber-by-fiber using non-invasive MRI monitoring.

In this study non-invasive low field magnetic resonance imaging (MRI) technology was used to monitor fouling induced changes in fiber-by-fiber hydrodynamics inside a multi-fiber hollow fiber membrane module containing 401 fibers. Using structural and velocity images the fouling evolution of these membrane modules were shown to exhibit distinct trends in fiber-by-fiber volumetric flow, with increasing fouling causing a decrease in the number of flow active fibers. This study shows that the fouling rate is not evenly distributed over the parallel fibers, which results in a broadening of the fiber to fiber flowrate distribution. During cleaning, this distribution is initially broadened further, as relatively clean fibers are cleaned more rapidly compared to clogged fibers. By tracking the volumetric flow rate of individual fibers inside the modules during the fouling-cleaning cycle it was possible to observe a fouling memory-like effect with residual fouling occurring preferentially at the outer edge of the fiber bundle during repeated fouling-cleaning cycle. These results demonstrate the ability of MRI velocity imaging to quantitatively monitor these effects which are important when testing the effectiveness of cleaning protocols due to the long term effect that residual fouling and memory-like effect may have on the operation of membrane modules.

Detection of biological uranium reduction using magnetic resonance.

The conversion of soluble uranyl ions (UO2²âº) by bacterial reduction to sparingly soluble uraninite (UO2(s)) is being studied as a way of immobilizing subsurface uranium contamination. Under anaerobic conditions, several known types of bacteria including iron and sulfate reducing bacteria have been shown to reduce U (VI) to U (IV). Experiments using a suspension of uraninite (UO2(s)) particles produced by Shewanella putrefaciens CN32 bacteria show a dependence of both longitudinal (T1) and transverse (T2) magnetic resonance (MR) relaxation times on the oxidation state and solubility of the uranium. Gradient echo and spin echo MR images were compared to quantify the effect caused by the magnetic field fluctuations (T*2) of the uraninite particles and soluble uranyl ions. Since the precipitate studied was suspended in liquid water, the effects of concentration and particle aggregation were explored. A suspension of uraninite particles was injected into a polysaccharide gel, which simulates the precipitation environment of uraninite in the extracellular biofilm matrix. A reduction in the T2 of the gel surrounding the particles was observed. Tests done in situ using three bioreactors under different mixing conditions, continuously stirred, intermittently stirred, and not stirred, showed a quantifiable T2 magnetic relaxation effect over the extent of the reaction.

Novel Magnetic Resonance Measurements of Fouling in Operating Spiral Wound Reverse Osmosis Membrane Modules.

A novel magnetic resonance measurement (MRM) protocol for non-invasive monitoring of fouling in spiral wound reverse osmosis (SWRO) membrane modules is demonstrated. Sodium alginate was used to progressively foul a commercial SWRO membrane at industrially relevant operating conditions in a circulating flow loop. The MRM protocol showcased the following: (i) earlier, more sensitive detection and quantification of fouling in the membrane module compared to feed-channel pressure drop. This was achieved using appropriate detection of the total nuclear magnetic resonance (NMR) signal. (ii) 2D cross-sectional imaging of the location of the accumulated foulant material; this was preferentially located adjacent to the membrane spacer sheet nodes, which was subsequently confirmed by a module autopsy. This image contrast, which could also readily differentiate the membrane, feed spacer and permeate spacer regions, was realised based on differences in the NMR relaxation parameter, T2,eff. (iii) High frequency acquisition of 2D cross-sectional velocity images of the module revealing very localised flow channelling in response to gradual foulant accumulation which impacted significantly on the flow pattern within the central permeate tube. Collectively this NMR/MRI measurement protocol provides a powerful analysis tool for the evolution of fouling in such complex modules, thus ultimately enabling more informed module design.

Simultaneous Gaussian and exponential inversion for improved analysis of shales by NMR relaxometry.

Nuclear magnetic resonance (NMR) relaxometry is commonly used to provide lithology-independent porosity and pore-size estimates for petroleum resource evaluation based on fluid-phase signals. However in shales, substantial hydrogen content is associated with solid and fluid signals and both may be detected. Depending on the motional regime, the signal from the solids may be best described using either exponential or Gaussian decay functions. When the inverse Laplace transform, the standard method for analysis of NMR relaxometry results, is applied to data containing Gaussian decays, this can lead to physically unrealistic responses such as signal or porosity overcall and relaxation times that are too short to be determined using the applied instrument settings. We apply a new simultaneous Gaussian-Exponential (SGE) inversion method to simulated data and measured results obtained on a variety of oil shale samples. The SGE inversion produces more physically realistic results than the inverse Laplace transform and displays more consistent relaxation behavior at high magnetic field strengths. Residuals for the SGE inversion are consistently lower than for the inverse Laplace method and signal overcall at short T2 times is mitigated. Beyond geological samples, the method can also be applied in other fields where the sample relaxation consists of both Gaussian and exponential decays, for example in material, medical and food sciences.

Magnetic resonance diffusion and relaxation characterization of water in the unfrozen vein network in polycrystalline ice and its response to microbial metabolic products.

Polycrystalline ice, as found in glaciers and the ice sheets of Antarctica, is a low porosity porous media consisting of a complicated and dynamic pore structure of liquid-filled intercrystalline veins within a solid ice matrix. In this work, Nuclear Magnetic Resonance measurements of relaxation rates and molecular diffusion, useful for probing pore structure and transport dynamics in porous systems, were used to physically characterize the unfrozen vein network structure in ice and its response to the presence of metabolic products produced by V3519-10, a cold tolerant microorganism isolated from the Vostok ice core. Recent research has found microorganisms that can remain viable and even metabolically active within icy environments at sub-zero temperatures. One potential mechanism of survival for V3519-10 is secretion of an extracellular ice binding protein that binds to the prism face of ice crystals and inhibits ice recrystallization, a coarsening process resulting in crystal growth with ice aging. Understanding the impact of ice binding activity on the bulk vein network structure in ice is important to modeling of frozen geophysical systems and in development of ice interacting proteins for biotechnology applications, such as cryopreservation of cell lines, and manufacturing processes in food sciences. Here, we present the first observations of recrystallization inhibition in low porosity ice containing V3519-10 extracellular protein extract as measured with Nuclear Magnetic Resonance and Magnetic Resonance Imaging.

Preasymptotic hydrodynamic dispersion as a quantitative probe of permeability.

We interpret a generalized short-time expansion of stochastic hydrodynamic dispersion dynamics in the case of small Reynolds number flow through macroscopically homogenous permeable porous media to directly determine hydrodynamic permeability. The approach allows determination of hydrodynamic permeability from pulsed field gradient spin-echo nuclear magnetic resonance measurement of the short-time effective hydrodynamic dispersion coefficient. The analytical expansion of asymptotic dynamics agrees with experimental NMR data and lattice Boltzmann simulation of hydrodynamic dispersion in consolidated random sphere pack media.

Microbial and algal alginate gelation characterized by magnetic resonance.

Advanced magnetic resonance (MR) relaxation and diffusion correlation measurements and imaging provide a means to non-invasively monitor gelation for biotechnology applications. In this study, MR is used to characterize physical gelation of three alginates with distinct chemical structures; an algal alginate, which is not O-acetylated but contains poly guluronate (G) blocks, bacterial alginate from Pseudomonas aeruginosa, which does not have poly-G blocks, but is O-acetylated at the C2 and/or C3 of the mannuronate residues, and alginate from a P. aeruginosa mutant that lacks O-acetyl groups. The MR data indicate that diffusion-reaction front gelation with Ca(2+) ions generates gels of different bulk homogeneities dependent on the alginate structure. Shorter spin-spin T(2) magnetic relaxation times in the alginate gels that lack O-acetyl groups indicate stronger molecular interaction between the water and biopolymer. The data characterize gel differences over a hierarchy of scales from molecular to system size.