Browsing by Subject "Reverse osmosis"

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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.
Investigating the effectiveness and safety of Earth Science Labs' disinfectants for reverse osmosis membranes
(2023-04-21) Hong, Noheul; Kumar, Manish; Liljestrand, Howard M. (Howard Michael)
Reverse osmosis (RO) systems are vulnerable to biofouling and scaling, which require disinfectants and antiscalants to maintain efficiency. In this study, we evaluated the performance of four disinfectant and/or scaling prevention products from Earth Science Labs - EarthTec QZ, MetalShield, Kleen-Break, and PABP-P - in comparison with commonly used monochloramine. The study investigated the damage that these disinfectants could potentially cause to commercial polyamide RO membranes. We characterized and tested the performance of commercial brackish water RO membranes treated with the four disinfectants for a typical lifetime of usage expected for them (7 years at 1 ppm, i.e., 61,320 ppmh) and compared with untreated RO membranes and monochloramine-treated membranes. The study found that the Earth Science Labs disinfectants did not cause any damage to RO membranes, particularly when compared to monochloramine, which is widely used in water reuse settings to prevent biofouling in RO membranes. The study concludes that all target solutions have minimal damage when compared to monochloramine to commercial BW30 membranes.
Optimization of natural organic matter removal by a hybrid ED-NF/RO membrane system
(2019-08-08) Kum, Soyoon; Lawler, Desmond F.; Katz, Lynn Ellen; Freeman, Benny D.; Werth, Charles J.; Liljestrand, Howard M.
Natural Organic Matter (NOM) reacts with Cl₂ and other disinfectants to form potentially carcinogenic disinfection byproducts (DBPs) in drinking water. NOM can be effectively removed by nanofiltration (NF) and reverse osmosis (RO), but NOM fouling on the membrane is the major challenge for applying membrane processes to natural waters. Furthermore, the presence of divalent cations has been shown to increase fouling associated with NOM. Therefore, pretreatment for the removal of cations prior to NF or RO could provide a cost-effective membrane system that allows for control of the final effluent water composition as well as extends the operation period for NF. The key to this hybrid approach is that electrodialysis (ED) can be used as pretreatment option to remove most ions while achieving minimal removal of NOM. In the hybrid process, the diluate from the ED system, containing few inorganic ions but NOM at nearly the influent concentration, is treated with NF. Subsequently, the concentrate from ED is mixed with the NF permeate to yield a water with nearly the original ion concentration and dramatically lowered NOM. To make this hybrid system viable as a full-scale treatment process, a thorough understanding of the system performance is required. Thus, this research evaluated the hybrid ED-NF/RO system for application to drinking water treatment in three phases. First, a substantial experimental program on ED alone, NF or RO alone, and ED followed by NF determined membrane (ED and NF/RO) characteristics important for this hybrid process and the effects of different ionic makeup and NOM characteristics. Subsequently, a preliminary economic analysis was performed, and that was followed with a life cycle assessment, emphasizing environmental and public health parameters. All three phases of the research confirmed that this hybrid process could have a niche in the drinking water industry, particularly for small plants (<13,300 m³/d) treating waters with moderate to high hardness and NOM concentrations in their supply. The life cycle assessment suggested that the lower chemical requirements of the hybrid system will produce fewer human health effects and environmental impacts compared to two other drinking water treatment systems targeting high TOC removal.
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.
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.
Reverse osmosis-based water management for US shale fields
(2018-09-11) Kar, Aritra; Bahadur, Vaibhav
Natural gas worth upto 50 billion USD (4% of global production) is flared in oilfields globally, with the US ranked 4th among top flaring nations. Venting and flaring of gas are very common, due to absence of economically viable alternatives. This waste gas can instead be used to produce water on an industrial scale. This study analyzes and compares the technical performance of three methods to produce water using excess natural gas. The first method involves using this gas to power reverse osmosis systems that treat flowback water from oil-gas production wells. While reverse osmosis has primarily been used for desalination, it is possible to use it to treat flowback water and brackish water up to certain total dissolved solids (TDS) levels. The second method involves using this waste gas to power thermal desalination units to treat flowback and brackish water. The third technique uses waste gas-powered refrigeration systems to produce the cooling capacity to enable large-scale dehumidification-based water production from the atmosphere. This method does not rely upon any water sources but is instead strongly dependent on ambient weather conditions. The work develops an improved version of the effectiveness-mass transfer units model to quantify the technical performance of excess natural-gas based reverse osmosis systems. The technical performance of reverse osmosis systems is compared with the other two methods. The advantages and limitations of these three methods is discussed and analyzed from a technical and techno-economic standpoint. The results of this work suggest that the attractiveness of these methods is location-specific and depends on certain technical and environmental parameters associated with the three water production technologies.
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.
Silica fouling in reverse osmosis systems : the role of chemical interaction with the membrane surface
(2017-05-03) Kim, Kyunghwa; Lawler, Desmond F; Freeman, Benny D; Katz, Lynn E; Liljestrand, Howard M; Kinney, Kerry A
Silica fouling of reverse osmosis (RO) membranes occurs by the deposition of silica and the subsequent formation of a silica film on the membrane surface. Typically, RO membranes are polyamide membranes made of 1,3-benzenediamine (m-phenylenediamine) and trimesoyl chloride (1,3,5-benzentricarbonyl chloride), having carboxyl (-COOH) and amide (-CONH-) functionalized groups. However, understanding of silica deposition on the carboxyl/amide functionalized surface of the membrane is still unclear. The goal of this study was to advance the understanding of how the chemical bonding groups of polyamide membranes are affected by dissolved silicates and how the structural change of functionalized groups by silicates consequently influences fouling. To achieve this goal, silica fouling tests were carried out by using a crossflow reverse osmosis (RO) system, and the membrane coupons were analyzed by X-ray photoelectron spectrometer (XPS) and Attenuated total reflection – Fourier transform infrared spectroscopy (ATR – FTIR). The XLE membrane mainly used in this study is the fully aromatic polyamide membrane, composing of the aromatic/aliphatic (C-C/C-H), amide (N-C=O), and carboxyl (O-C=O) group. The silica uptake was accompanied with an increase of oxygen, indicating the formation of SiO₂ structure on the membrane surface. Due to the concentration polarization effects, highly concentrated silicates had great propensity to form a silica gel layer. As a result, a soft gel layer with high water content was formed. Then, the accumulated silica gel aged and became a more condensed (SiO₂)[subscript n] structure by expelling water molecules. Therefore, the ratio of oxygen to silica (O/Si) of condensed (SiO₂)[subscript n] network structure would be close to 2.0. This ratio of membrane exposed in a fouling test to oversaturated silica feed water was 1.99, while a similar membrane exposed to undersaturated silica feed water was 11.38. After silica deposition, the aromatic/aliphatic group decreased significantly and the silicon carbide (Si-C) and hydroxyl (C-OH) groups newly appeared. These bonding changes showed that the aromatic /aliphatic group partially transformed to the hydroxyl group and the silica bonded to the carbon source in the carboxyl group by substituting for the oxygen. The carboxyl group decreased as the silica concentration in the feed water increased. Interestingly, the decrease of carboxyl group involved the flux decline. The carboxyl group came from the hydrolysis of trimesoyl chloride, giving hydrophilicity and consequently increasing water permeability. The carboxyl group was not recovered by the membrane cleaning. This basic (pH > 10.0) cleaning procedure decreased the ratio of O/Si from 11.38 to 1.41, indicating the oxygen lost in the silica deposition. The results of this study could contribute to the fundamental understanding to improve antifouling property through appropriate surface modifications that can alleviate the deposition of silica foulants or prevent the deformation of chemical bonding groups of polyamide membranes.