Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Non-destructive assessment of household reverse osmosis water treatment membrane biofouiling(Montana State University - Bozeman, College of Engineering, 2015) Markwardt, Stephen Donald; Chairperson, Graduate Committee: Anne CamperReverse osmosis (RO) membrane treatment is well known for its ability to desalinate sea and brackish waters on a massive scale in large treatment plants. Conversely, RO membranes are also used to treat freshwater from questionable sources at the point of use. Both types of systems suffer from the negative effects of membrane fouling. There are four basic types of fouling: inorganic, colloidal, organic, and biofouling. Traditional methods for assessing fouling either cannot differentiate between the fouling types or destroy the membrane in the process. Currently, many new and innovative methods to non-destructively assess the degree and type of fouling inside a membrane unit are being researched. Most of these methods require the use of expensive electrodes and equipment which is not economical for point of use systems. This research was aimed at determining economical non-destructive methods to assess biofouling in point of use RO membrane treatment systems. Experimentation was performed on three parallel household RO membrane units operated under controlled feed water conditions to promote biofouling, inorganic fouling and a combination of both. Operational and biological parameters were monitored throughout the systems' lifespan. Membrane autopsies were also done to assess the degree and type of fouling. Statistical models were performed on the operational data to determine statistically relevant parameters between the fouling types that were subsequently validated by the membrane autopsies. Several non-destructive methods to assess the presence of biofouling were determined. Permeate flow rates decreased in a significantly different way when biofouling was present compared to when it was not. Large increases in permeate conductivity were also noted in membranes suffering from biofouling while they were not observed in membranes that had been inorganically fouled. The concentration of cell clumps in the retentate also increased in membranes experiencing biofouling while they did not increase in membranes that were inorganically fouled. These methods were found to not be sensitive enough to provide early warning for the presence of biofouling. However, these methods could be used to conveniently and economically assess the types of fouling problems being experienced household RO systems.Item Modeling the non-linear response of mixed culture biofilm structures to turbulent flow(Montana State University - Bozeman, College of Engineering, 2004) Towler, Brett William; Chairperson, Graduate Committee: Ladean McKittrick.Microbial biofouling of wetted interfaces can negatively impact the hydrodynamic performance of pressurized conduits. These impacts are due, in part, to the material properties of biofilm, yet few studies have examined this polymeric substance in the context of a constitutive relation. The goal of this research was two-fold; 1) to determine a suitable constitutive model for a mixed-culture biofilm and 2) use this material model in a numerical simulation to evaluate biofilm mechanical behavior in response to varying hydrodynamic conditions. Creep tests revealed that these biofilms may be classified as viscoelastic fluids. Furthermore, results indicated the presence of viscous, time-dependent and instantaneous components to the biofilm compliance functions. A regression analysis (r2 = 0.8819) supported the treatment of these samples as linear viscoelastic fluids within the stress range of 0.1 Pa to 0.5 Pa. A specific linear viscoelastic constitutive equation was then determined by fitting experimental results to analytical solutions using an optimization algorithm. It was found that the Burger material model closely approximated the behavior of all samples. A numerical fluid-structure interface model was then developed and employed in a parametric study to investigate biofilm behavior. The effect of the Burger material parameters, mean flow velocity and biofilm size were examined. Simulations showed that weaker or softer biofilms (characterized by lower elastic moduli) were highly susceptible to lift forces. Additionally, polar diagrams were generated by plotting the coefficients of drag versus lift. The plots suggested that in the first few seconds after loading, the deformation paths taken by hemispherical biofilms are largely insensitive to specific material coefficients. Moreover, the diagrams illustrated that the effects of biofilm strength, size and channel velocity on displacement were predictable. These relationships may lead to the development of a simple, yet accurate method for predicting the hydrodynamic forces acting on an attached biofilm.Item Biocide action of chlorine on Pseudomonas aeruginosa biofilm(Montana State University - Bozeman, College of Engineering, 1991) Wende, Ewout van der