Browsing by Subject "Reverse osmosis"
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Item EVALUATION AND INHIBITION OF BIOFILM ATTACHMENT TO MEMBRANE SURFACES IN WATER AND WASTEWATER TREATMENT SYSTEMS(2010-12) Low, Darryl; Morse, Audra; Hamood, Abdul N.; Reid, Ted W.; Song, LianfaAs engineers’ understanding of the biological treatment systems in water and wastewater systems increased, advanced technologies have emerged. These included combining biological systems with other treatment systems such as membrane technologies. The overall objective of this research was to evaluate the impacts of bacterial attachment to membranes during treatment operations and propose an antimicrobial coating to maximize membrane performance. Membranes from a small scale, membrane aerated biological unit were removed and analyzed for continued performance after an extended operational period. Afterwards, a selenium based antimicrobial coating was developed to prevent microbial attachment without harming membrane performance. This coating was applied to reverse osmosis membranes and the coating’s efficacy to prevent biofilm growth on the reverse osmosis membrane surface was investigated. Ultimately, the selenium coating displayed a strong inhibition against bacterial attachment and biofilm formation. Selenium’s capability to catalytically generate superoxide molecules was effective in damaging bacterial cell membranes resulting in lysis. Both Gram positive (S. aureus) and Gram negative (E. coli) bacteria showed high susceptibility to the superoxide attack. Attachment utilizing the selenocystamine molecule via peptide bond to a modified membrane surface was selected as the desired attachment method. Selenocystamine allowed for the RO membrane to maintain its higj permeate flux without overly diminishing membrane rejection. Attachment of selenium to membrane surfaces may be a valuable technology to allow for continuous performance even in the harsh operating conditions present in biological reactors.Item Improving recovery in reverse osmosis desalination of inland brackish groundwaters via electrodialysis(2010-08) Walker, William Shane, 1981-; Lawler, Desmond F.; Freeman, Benny D.; Katz, Lynn E.; Kinney, Kerry A.; Liljestrand, Howard M.As freshwater resources are limited and stressed, and as the cost of conventional drinking water treatment continues to increase, interest in the development of non-traditional water resources such as desalination and water reuse increases. Reverse osmosis (RO) is the predominant technology employed in inland brackish groundwater desalination in the United States, but the potential for membrane fouling and scaling generally limits the system recovery. The general hypothesis of this research is that electrodialysis (ED) technology can be employed to minimize the volume of concentrate waste from RO treatment of brackish water (BW) and thereby improve the environmental and economic feasibility of inland brackish water desalination. The objective of this research was to investigate the performance sensitivity and limitations of ED for treating BWRO concentrate waste through careful experimental and mathematical analysis of selected electrical, hydraulic, and chemical ED variables. Experimental evaluation was performed using a laboratory-scale batch-recycle ED system in which the effects of electrical, hydraulic, and chemical variations were observed. The ED stack voltage showed the greatest control over the rate of ionic separation, and the specific energy invested in the separation was approximately proportional to the applied voltage and equivalent concentration separated. An increase in the superficial velocity showed marginal improvements in the rate of separation by decreasing the thickness of the membrane diffusion boundary layers. A small decrease in the nominal recovery was observed because of water transport by osmosis and electroosmosis. Successive concentration of the concentrate by multiple ED stages demonstrated that the recovery of BWRO concentrate could significantly improve the overall recovery of inland BWRO systems. A mathematical model for the steady-state performance of an ED stack was developed to simulate the treatment of BWRO concentrates by accounting for variation of supersaturated multicomponent solution properties. A time-dependent model was developed that incorporated the steady-state ED model to simulate the batch-recycle experimentation. Comparison of the electrical losses revealed that the electrical resistance of the ion exchange membranes becomes more significant with increasing solution salinity. Also, a simple economic model demonstrated that ED could feasibly be employed, especially for zero-liquid discharge.Item Polyamide desalination membrane characterization and surface modification to enhance fouling resistance(2010-05) Van Wagner, Elizabeth Marie; Freeman, B. D. (Benny D.); Sharma, Mukul M.; Paul, Donald R.; Bonnecaze, Roger T.; Lawler, Desmond F.; Mickols, William E.The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterization of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ([microgram]/cm2), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling.Item Preparation and characterization of disulfonated polysulfone films and polyamide thin film composite membranes for desalination(2011-12) Xie, Wei, 1982-; Freeman, B. D. (Benny D.); Paul, Donald R.; Sanchez, Isaac C.; Bielawski, Christopher W.; McGrath, James E.The current reverse osmosis desalination membrane market is dominated by aromatic polyamide thin film composite (TFC) membranes. However, these polyamide membranes suffer from poor resistance to continual exposure to oxidizing agents such as chlorine in desalination applications. To overcome these problems, we have synthesized and characterized a new generation of materials, disulfonated poly(arylene ether sulfone) (BPS) random copolymer, for desalination membranes. A key technical feature of these new materials is their high tolerance to chlorine in feed water and their excellent reproducibility in synthesis. In this study, water and sodium chloride solubility, diffusivity and permeability in BPS copolymers were measured for both acid and salt form samples at sulfonation levels from 20 to 40 mol percent. The hydrophilicity of these materials, based on water uptake, increased significantly as sulfonation level increased. The water and salt diffusivity and permeability were correlated with water uptake, consistent with expectations from free volume theory. In addition, a tradeoff was observed between water/salt solubility, diffusivity, and permeability selectivity and water solubility, diffusivity and permeability, respectively. The influence of cation form and degree of sulfonation on free volume, as probed via positron annihilation lifetime spectroscopy (PALS), was determined in BPS random copolymers in both the dry and hydrated states. PALS-based free volume data for hydrated polymers were correlated with water and salt transport properties. The influence of processing history on transport properties of BPS films was also studied. Potassium form BPS films having a 32 mol% sulfonation level were acidified using solid state and solution routes. Additionally, several films were subjected to various thermal treatments in the solid state. The influence of acidification, thermal treatment, and counter-ion form on transport properties was investigated. Finally, the influence of synthesis methods of polyamide TFC membranes from m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization on transport properties is reported. Then, a disulfonated diamine monomer (S-BAPS) was used instead of MPD to prepare TFC membranes. The resulting membranes exhibited reduced chlorine tolerance than those prepared from MPD. However, introduction of S-BAPS to the MPD/TMC polymerization system increased the fouling resistance of the resulting polyamide TFC membranes.Item Salt solubility measurements in partially disulfonated poly(arylene ether sulfone) for reverse osmosis water purification applications(2010-05) Passaniti, Linda Kimberly; Paul, Donald R.; Freeman, Benny D.Partially disulfonated poly(arylene ether sulfone) (BPS) membranes have shown great promise as robust, chlorine tolerant alternatives to the current polyamide materials as reverse osmosis desalination membranes for water purification. The random copolymers are synthesized by direct polymerization of a disulfonated monomer (3,3’-disulfonato-4,4’-dichlorodiphenyl sulfone (SDCDPS)) and other monomers (4,4’-dichlorodiphenyl sulfone (DCDPS) and 4,4’-biphenol (BP)). The sulfonation of the materials adds necessary hydrophilic character and adjusting the percent sulfonation of the material changes the water and salt uptake of the material. Additionally, sulfonation causes the membranes to be charged, making them ion exchangers in which anions are partially excluded from the membrane, thus affecting the partitioning of salt in the membrane. The amount of sodium chloride present in the membrane after equilibration with external soaking solutions of varying concentrations of sodium chloride was measured by measuring the amount of individual ions, i.e., the sodium cation and chloride anion, separately. One area in which this work is unique is that it sought to measure the concentrations of the ions independently of one another. The analysis of sodium and chloride has shown the concentration of sodium in the membrane to be significantly greater than that of chloride, where the uptake of chloride is the limiting factor in the uptake of sodium chloride. The trends in the concentrations as well as in the partition coefficients of the ions are consistent with Donnan Exclusion.Item The impact of biological pretreatment on reverse osmosis performance in space flight applications(2007-12) Crawley, Jason; Morse, Audra; Jackson, Andrew W.; Song, Lianfa; Anderson, ToddRO is a treatment technology likely to be used for the recovery of wastewater on board long duration, manned space flights. As with terrestrial RO applications, concentration polarization and fouling lead to decreasing productivity and increasing energy demands with time. These problems are further complicated in a closed loop environment that demands a high level of recovery and quality. Physiochemical and biological pretreatment options can enhance the performance of the RO system. Physiochemical pretreatment is not always desirable in the application of long duration space flight because the transport and stowage of consumables can be cost prohibitive. Also, the transport and stowage of hazardous materials such as strong acids and bases is not desirable. Biological pretreatment is a low energy option that requires only a limited supply of consumables. Additionally, biological pretreatment is a proven terrestrial technology that is well understood. To determine the degree to which the incorporation of biological treatment enhances RO performance, a series of bench scale experiments were performed. The RO performance was measured in terms of permeate flux decline, solute rejection, and flow resistances. A mass balance and observed solute concentrations also helped to determine the fate of selected solutes. The gel layer model was used to evaluate the permeate flux for each of the experiments. Observed resistances also indicate that biological pretreatment alleviates the degree of fouling. Results indicate that enhanced urea hydrolysis, pH decrease, and carbon oxidation serve as the primary benefits of biological pretreatment.