Lucas K. McGrath

Field Demonstrations of Chemiresistor and Surface Acoustic Wave Microchemical Sensors at the Nevada Test Site

Microchemical sensors developed at Sandia National Laboratories were tested at the Nevada Test Site as part of the Advanced Monitoring Systems Initiative program. Two sensors, the chemiresistor sensor and the surface-acoustic-wave (SAW) sensor, were evaluated in the tests. Both sensors rely on sorption of chemicals onto polymer films to produce a change in an electrical signal that can be recorded and calibrated, but different transduction mechanisms are used. The primary purpose of the tests was to evaluate the feasibility of using these devices in potentially long-term, unattended applications such as long-term monitoring of subsurface contaminants. A complete monitoring system was developed that provided real-time monitoring of the sensors via the internet. Engineering issues such as sensor packaging, data acquisition, power requirements, and telemetry were addressed during the development and testing of the sensor systems. In addition, issues such as data processing, noise, and interferences from fluctuating environmental variables were also encountered and evaluated during the field tests. Results showed that both sensors could be operated remotely and continuously for long-term monitoring applications using commercial data-acquisition systems and custom-designed packaging. Both the chemiresistor and SAW sensors experienced drift in the signal and were impacted by fluctuations in temperature and humidity. However, results from the chemiresistor showed that exposure to large concentrations of contaminants (e.g., trichloroethylene) overwhelmed the fluctuations caused by temperature and humidity variations. Results also showed that the chemiresistor sensor exhibited better stability and sensitivity than the SAW sensor for the conditions and analytes that were tested, which was contrary to initial theoretical predictions. a a a a a

Development of LTCC Smart Channels for Integrated Chemical, Temperature, and Flow Sensing

This paper describes the development of “smart” channels that can be used simultaneously as a fluid channel and as an integrated chemical, temperature, and flow sensor. The uniqueness of this device lies in the fabrication and processing of low-temperature co-fired ceramic (LTCC) materials that act as the common substrate for both the sensors and the channel itself. Devices developed in this study have employed rolled LTCC tubes, but grooves or other channel shapes can be fabricated depending on the application requirements. The chemical transducer is fabricated by depositing a conductive polymer “ink” across a pair of electrodes that acts as a chemical resistor (chemiresistor) within the rolled LTCC tube. Volatile organic compounds passing through the tube are absorbed into the polymers, causing the polymers to reversibly swell and change in electrical resistance. The change in resistance is calibrated to the chemical concentration. Multiple chemiresistors have been integrated into a single smart channel...

Systematic analysis of micromixers to minimize biofouling on reverse osmosis membranes.

Micromixers, UV-curable epoxy traces printed on the surface of a reverse osmosis membrane, were tested on a cross-flow system to determine their success at reducing biofouling. Biofouling was quantified by measuring the rate of permeate flux decline and the median bacteria concentration on the surface of the membrane (as determined by fluorescence intensity counts due to nucleic acid stains as measured by hyperspectral imaging). The micromixers do not appear to significantly increase the pressure needed to maintain the same initial permeate flux and salt rejection. Chevrons helped prevent biofouling of the membranes in comparison with blank membranes. The chevron design controlled where the bacteria adhered to the membrane surface. However, blank membranes with spacers had a lower rate of permeate flux decline than the membranes with chevrons despite having greater bacteria concentrations on their surfaces. With better optimization of the micromixer design, the micromixers could be used to control where the bacteria will adhere to the surface and create a more biofouling resistant membrane that will help to drive down the cost of water treatment.

pH modification for silica control

ABSTRACT Lowering solution pH slows the polymerization of silica and formation of silica scale. In batch systems, lowering the pH of approximately 200 ppm silica solutions prevents scale formation for over 300 h. Silica scale forms most quickly near pH 8. Solutions with pH 3.6–3.7 can maintain silica levels of 1,000–3,000 ppm for roughly 90 h. Bench-scale membrane testing showed that silica scale formation lag times of approximately 72 h were achievable after lowering the pH to 4.5–4.7, which might allow flushing of silica-laden solutions through, for example, flow reversal, before scale formation occurs during water treatment.

Joint physical and numerical modeling of water distribution networks.

This report summarizes the experimental and modeling effort undertaken to understand solute mixing in a water distribution network conducted during the last year of a 3-year project. The experimental effort involves measurement of extent of mixing within different configurations of pipe networks, measurement of dynamic mixing in a single mixing tank, and measurement of dynamic solute mixing in a combined network-tank configuration. High resolution analysis of turbulence mixing is carried out via high speed photography as well as 3D finite-volume based Large Eddy Simulation turbulence models. Macroscopic mixing rules based on flow momentum balance are also explored, and in some cases, implemented in EPANET. A new version EPANET code was developed to yield better mixing predictions. The impact of a storage tank on pipe mixing in a combined pipe-tank network during diurnal fill-and-drain cycles is assessed. Preliminary comparison between dynamic pilot data and EPANET-BAM is also reported.

Analysis of micromixers and biocidal coatings on water-treatment membranes to minimize biofouling.

Biofouling, the unwanted growth of biofilms on a surface, of water-treatment membranes negatively impacts in desalination and water treatment. With biofouling there is a decrease in permeate production, degradation of permeate water quality, and an increase in energy expenditure due to increased cross-flow pressure needed. To date, a universal successful and cost-effect method for controlling biofouling has not been implemented. The overall goal of the work described in this report was to use high-performance computing to direct polymer, material, and biological research to create the next generation of water-treatment membranes. Both physical (micromixers - UV-curable epoxy traces printed on the surface of a water-treatment membrane that promote chaotic mixing) and chemical (quaternary ammonium groups) modifications of the membranes for the purpose of increasing resistance to biofouling were evaluated. Creation of low-cost, efficient water-treatment membranes helps assure the availability of fresh water for human use, a growing need in both the U. S. and the world.

Use of ceragenins to create novel biofouling resistant water-treatment membranes.

Scoping studies have demonstrated that ceragenins, when linked to water-treatment membranes have the potential to create biofouling resistant water-treatment membranes. Ceragenins are synthetically produced molecules that mimic antimicrobial peptides. Evidence includes measurements of CSA-13 prohibiting the growth of and killing planktonic Pseudomonas fluorescens. In addition, imaging of biofilms that were in contact of a ceragenin showed more dead cells relative to live cells than in a biofilm that had not been treated with a ceragenin. This work has demonstrated that ceragenins can be attached to polyamide reverse osmosis (RO) membranes, though work needs to improve the uniformity of the attachment. Finally, methods have been developed to use hyperspectral imaging with multivariate curve resolution to view ceragenins attached to the RO membrane. Future work will be conducted to better attach the ceragenin to the RO membranes and more completely test the biocidal effectiveness of the ceragenins on the membranes.

Linking ceragenins to water-treatment membranes to minimize biofouling.

Ceragenins were used to create biofouling resistant water-treatment membranes. Ceragenins are synthetically produced antimicrobial peptide mimics that display broad-spectrum bactericidal activity. While ceragenins have been used on bio-medical devices, use of ceragenins on water-treatment membranes is novel. Biofouling impacts membrane separation processes for many industrial applications such as desalination, waste-water treatment, oil and gas extraction, and power generation. Biofouling results in a loss of permeate flux and increase in energy use. Creation of biofouling resistant membranes will assist in creation of clean water with lower energy usage and energy with lower water usage. Five methods of attaching three different ceragenin molecules were conducted and tested. Biofouling reduction was observed in the majority of the tests, indicating the ceragenins are a viable solution to biofouling on water treatment membranes. Silane direct attachment appears to be the most promising attachment method if a high concentration of CSA-121a is used. Additional refinement of the attachment methods are needed in order to achieve our goal of several log-reduction in biofilm cell density without impacting the membrane flux. Concurrently, biofilm forming bacteria were isolated from source waters relevant for water treatment: wastewater, agricultural drainage, river water, seawater, and brackish groundwater. These isolates can be used for future testing of methods to control biofouling. Once isolated, the ability of the isolates to grow biofilms was tested with high-throughput multiwell methods. Based on these tests, the following species were selected for further testing in tube reactors and CDC reactors: Pseudomonas ssp. (wastewater, agricultural drainage, and Colorado River water), Nocardia coeliaca or Rhodococcus spp. (wastewater), Pseudomonas fluorescens and Hydrogenophaga palleronii (agricultural drainage), Sulfitobacter donghicola, Rhodococcus fascians, Rhodobacter katedanii, and Paracoccus marcusii (seawater), and Sphingopyxis spp. (groundwater). The testing demonstrated the ability of these isolates to be used for biofouling control testing under laboratory conditions. Biofilm forming bacteria were obtained from all the source water samples.

Interaction of Introduced Biological Agents with Biofilms in Water Distribution Systems

Basic research is needed to better understand the potential risk of dangerous biological agents that are unintentionally or intentionally introduced into a water distribution system. Included in this research is an assessment of how bio-pathogens will interact with biofilms growing on water-distribution system pipe-wall surfaces. Experiments are being run at Sandia National Laboratories to better understand the impact of biofilms on pathogen dissemination through water distribution systems, both before and after decontamination of the system. The hope is that these data can be fed into numerical tools that quantify the risk and associated uncertainty of pathogenic biological agents being introduced into water distribution systems and the effects of biofilms on this risk. In addition these data could be used in numerical tools that assess decontamination methods for water distribution system networks. Reproducible Pseudomonas fluorescens biofilms were grown in annular reactors with plate counts on the order of 10 5 and 10 6 CFU/cm 2 . A series of pathogen-introduction experiments, where both 1-μm-diameter fluorescently labeled polystyrene microspheres and Bacillus cereus (as a surrogate for B. anthracis ) were introduced in the annular reactor after the P. fluorescens biofilms have reached stationary phase. Integration of the pathogens in the biofilms was monitored by gram-specific plating techniques and epifluorescent microscopy. Fluorescent nucleic-acid stains were used to visually differentiate the gram-positive ( B. cereus ) and gram-negative ( P. fluorescens ) organisms. Fluorescence spectrophotometry was used to measure the microsphere concentrations. Variables examined in the experiments include initial pathogen concentration, rotation speed of the inner cylinder of the annular reactor (shear force), and biofilm plate counts prior to the start of the experiment. Chlorine was added to the system after the pathogen had at least 14 days in contact with the biofilms and the impact of the chlorine on pathogen concentration in the biofilms was monitored. Pathogens are observed to get integrated in the biofilms at a relatively constant concentration until the start of the chlorine treatment. The higher the initial pathogen concentration and the higher the initial biofilm plate counts prior the pathogen introduction, the more pathogen integrated into the biofilms. A decrease in pathogen concentration to below the detection limit in the biofilms and the reactor water was observed during the chlorine treatment. From the results of one experiment, it appears that the pathogens do not recover after termination of the chlorine treatment. However, more data need to be collected to confirm these results. These results indicated that biofilms may act as a safe harbor for bio-pathogens in drinking water systems, making it difficult to decontaminate the systems. Chlorination of the system appears to be effective in decontaminating the system in the annular reactor geometry at the concentrations that we used. Additional experiments are being run to further test this observation. As these experiments cannot assess the effectiveness of chlorination at pipe junctions and because annular reactors have a higher surface area to volume ratio than pipe systems, the results from these experiments should also be tested in a system with a more complicated geometry that more closely matches water distribution systems. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).

Exploratory research into pathogen surface interactions.

In this short-duration project the research team was able to achieve growth of both drinking water biofilms and monospecific biofilms of Legionella pneurnophila. Preliminary comparative proteomic analyses were carried out on planktonic and biofilm-associated Legionella. After delay for completion of permitting and review by the director of the National Institutes for Allergy and Infectious Disease, the Utah 112 strain of Francisella novicida was obtained and preliminary culture and comparative proteomic analyses were carried out. Comprehensive literature searches and data mining were carried out on all research topics.