Ultra-low Pressure Reverse Osmosis Research Articles

Ultralow-pressure RO membrane element enhances neutral molecule rejection

Japan’s Toray Industries Inc continues to add products to its portfolio of reverse osmosis (RO) membrane elements. It has developed, and has recently started marketing, an ultralow-pressure RO membrane element that is designed for enhanced neutral molecule rejection. Here we look at the product and briefly explain how it is used in the electronics industry as an aid to manufacturing complex semiconductors.

Enhanced modelling and experimental validation of ultra-low pressure reverse osmosis membrane system for treatment of synthetic brackish water.

Water purification from brackish water sources has been acknowledged as one of the most promising ways to produce drinkable water in water-scarce areas. In this study, an ultra-low pressure reverse osmosis (ULPRO) membrane was numerically and experimentally investigated to produce drinking water by the removal of sodium chloride salt which provides further validation of the model from a practical perspective. An enhanced predictive model based on the Donnan-Steric Pore Model with dielectric exclusion (DSPM-DE) incorporating the osmotic effects was formulated in process simulation. The feed pressure and concentration were optimized as input variables and interaction between them was observed, while salt rejection and water recovery rate were taken as response attributes. The results obtained on the ULPRO membrane showed that the performance depends on the charge, steric, and dielectric effects. Furthermore, the enhanced model was validated with the experimental data attained from a laboratory-scale filtration system with good accuracy in the salt rejection and water recovery results. Comparing the enhanced DSPM-DE with the existing solution diffusion model reveals that the enhanced model predicts the membrane performance better and thereby qualifies itself as a reliable model for desalination of brackish water using ULPRO membrane.

A New Method for a Polyethersulfone-Based Dopamine-Graphene (xGnP-DA/PES) Nanocomposite Membrane in Low/Ultra-Low Pressure Reverse Osmosis (L/ULPRO) Desalination.

Herein we present a two-stage phase inversion method for the preparation of nanocomposite membranes for application in ultra-low-pressure reverse osmosis (ULPRO). The membranes containing DA-stabilized xGnP (xGnP-DA-) were then prepared via dry phase inversion at room temperature, varying the drying time, followed by quenching in water. The membranes were characterized for chemical changes utilizing attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The results indicated the presence of new chemical species and thus, the inclusion of xGnP-DA in the polyethersulfone (PES) membrane matrix. Atomic force microscopy (AFM) showed increasing surface roughness (Ra) with increased drying time. Scanning electron microscopy (SEM) revealed the cross-sectional morphology of the membranes. Water uptake, porosity and pore size were observed to decrease due to this new synthetic approach. Salt rejection using simulated seawater (containing Na, K, Ca, and Mg salts) was found to be up to stable at <99.99% between 1–8 bars operating pressure. After ten fouling and cleaning cycles, flux recoveries of <99.5% were recorded, while the salt rejection was <99.95%. As such, ULPRO membranes can be successfully prepared through altered phase inversion and used for successful desalination of seawater.

Feasibility of forward osmosis using ultra low pressure RO membrane and Glauber salt as draw solute for wastewater treatment

Glauber salt (sodium sulfate decahydrate, Na2SO4·10H2O) is presented as a viable draw solute in forward osmosis (FO) process for dewatering of textile wastewater and brackish water. A widely available, commercial, low cost ultra low pressure reverse osmosis membrane is used in a bench scale FO unit. Water flux of 7 L m−2 h−1, 4.3 L m−2 h−1 and 5.3 L m−2 h−1 were obtained with DI water, synthetic wastewater and industrial wastewater feed solution using 1.5 M Na2SO4 draw solution. Desalination of brackish water (0.25 NaCl) and sea water (0.6 M NaCl) yielded water flux of 4.5 L m−2 h−1 and 2.6 L m−2 h−1 respectively. A minimal reverse salt flux of 0.42 g m−2 h−1 was attained with 1 M Na2SO4 draw solution against DI feed water. The diffusion coefficient for the FO process was determined to be 0.8 × 10-9 m2 s−1 and the membrane solute resistivity value was 1.25 × 107 s m−1. Reversible fouling caused by scattered and non-uniform loose deposition of particles at the membrane surface was observed which was easily cleaned and 90% water flux could be restored. Recovery of draw solute was attempted by low pressure nanofiltration process using less energy. Good quality permeate containing negligible salt (<150 mg L−1 TDS) was generated at <5 atm. pressure. An alternative utilization of dilute Glauber salt solution for production of dilute fertilizer solution eliminating recovery process is proposed. Overall, the versatility and feasibility of the FO process with locally availableresources giving good performance has been established.

Synthesis, characterization and permeation performance of cellulose acetate/polyethylene glycol-600 membranes loaded with silver particles for ultra low pressure reverse osmosis

In order to tap the seemingly boundless problem of water scarcity, reverse osmosis (RO), has been formulated as a significant solution. However, RO technology, suffers by a major challenge of biofouling, which results in reduced production capacity and increased operation costs. Thus, there is an urgent demand to fabricate an appropriate disinfection membrane surface with maximum permeation performance. In this work, cellulose acetate/poly ethylene glycol membranes impregnated with silver particles were prepared by 2-stage phase inversion protocol. The Modified membranes were characterized for their compositional analysis, surface roughness, surface morphology, permeation properties, membrane hydraulic resistance and antibacterial activity. The presence of functional group was determined by FTIR spectra. The asymmetric surface morphology of membranes was elucidated from the scanning electron microscope. The varying nature of nodules and interstices spaces was observed in the images obtained by the atomic forced microscopy. The progressive decreased was observed in the surface roughness of membranes. The modification has significantly increased the flux and salt rejection capacity of membranes. All modified membranes exhibited remarkable antibacterial properties against gram negative Escherichia Coli. The synthesis of cellulose acetate membrane, doped with polyethylene glycol and modified with silver, provides a convenient way for the development of self-sterilized membranes.

Mechanism of removal of pharmaceuticals and personal care products by nanofiltration membranes

Much attention has been paid to pharmaceuticals and personal care products (PPCPs). Nanofiltration (NF) is a new type of separation technology developed between ultrafiltration and reverse osmosis (RO) in the mid-1980s, which is a continuation and development branch of the ultra-low pressure RO technology. PPCPs are a kind of water ubiquitous trace organics, and there are some disadvantages of the PPCPs, such as recalcitrance, accumulation of biological toxicity and long-term dangers, which gradually attracts the attention of the scientific community due to the harm to the environment and ecosystems. This paper analyses the latest research progress in this country and overseas, introducing the advantages on removal of the PPCPs by NF membranes, also recommending the mechanism of the removal process and influencing factors. The direction of future research is proposed as well.

4-Dimethylaminopyridine Promoted Interfacial Polymerization between Hyperbranched Polyesteramide and Trimesoyl Chloride for Preparing Ultralow-Pressure Reverse Osmosis Composite Membrane

We have presented a concept of ultralow-pressure reverse osmosis membrane based on hyperbranched polyesteramide through interfacial reaction promoted by pyridine derivate. In this strategy, a key catalyst of 4-dimethylaminopyridine, which can both eliminate the steric hindrance of acyl transfer reaction and facilitate the phase transfer in interfacial polymerization, is adopted to drive the formation of a thin film composite membrane from the hyperbranched polyesteramide and trimesoyl chloride. The results of the characterization demonstrate that a dense, rough, and hydrophilic active layer with a thickness of about 100 nm is formed when the 4-dimethylaminopyridine catalyst is used. The salt rejections for Na2SO4, NaCl, and MgSO4 of the as-prepared composite membrane are higher than 92%, especially for Na2SO4 with 98% rejection. The water fluxes reach about 30-40 L·m(-2)·h(-1) even at an operation pressure of 0.6 MPa. The membrane exhibits good chlorine-resistance ability but poor resistance abilities to acidic and alkaline solutions in the physical-chemical stability experiment. It is also found that the resultant membrane possesses excellent separation performance for PEG-200, showing a promising way to separate small organic molecules from water.

Removal of fluoride and total dissolved solids from coalbed methane produced water with a movable ultra-low pressure reverse osmosis system

The aim of this project was to establish an economical and environmentally benign technology for removing fluoride (F-) and total dissolved solids (TDS) from coalbed methane (CBM) produced water. The proposal involved a movable wastewater treatment system comprised of a flocculation sedimentation pretreatment unit and an ultra-low pressure reverse osmosis unit in Liulin County, Shanxi Province, China, where concentration of F- ranged from 1.3 to 18.2 mg/L and concentration of TDS ranged from 2800 to 6,600 mg/L. When the hydraulic load was 2–4 m3/day with the running mode in 10 h cycles at 10–15 days interval, the removal efficiency was 94.7% for F- and 98.1% for TDS with 55% water recovery from June to November 2011. Concentrations of F- and TDS in effluent were lower than the permissible discharge standard values of pollutants for irrigation and livestock. The flexible deployment and small footprint affordable was appropriate for removing pollutants from CBM mining areas with low water production and discommodiously decentralized treatment.

Modeling the impacts of feed spacer geometry on reverse osmosis and nanofiltration processes

Maximizing mass transfer and minimizing hydraulic losses in spiral wound elements is critical for designing effective and efficient reverse osmosis (RO) and nanofiltration (NF) processes. Herein we describe a multi-scale modeling approach, which links microscopic and macroscopic transport phenomena in spiral wound elements. Model simulations elucidate the impacts of feed spacer geometry on full-scale RO/NF system performance considering four representative water treatment scenarios: (1) RO membranes used to desalt ocean water, (2) low-pressure RO membranes used to desalt brackish water, (3) ultra-low pressure RO membranes used to purify wastewater, and (4) NF membranes used to soften a hard, fresh water. According to model simulations, feed spacer geometry had little impact on mass transfer; hence, engineering spacers to improve concentration polarization, trans-membrane osmotic pressure, or product water quality may prove difficult and yield limited benefits. In contrast, thinner filaments spread further apart significantly reduced hydraulic losses with negligible impacts to mass transfer. In addition, a few non-circular filament shapes produced even lower hydraulic losses, which might prove beneficial for RO/NF treatment of low salinity waters where hydraulic losses through spiral wound elements contribute significantly to the total process energy consumption. In high salinity waters, improved spacer designs may not significantly reduce energy consumption because hydraulic losses through spiral wound elements are relatively small.

Comparing nanofiltration and reverse osmosis for drinking water augmentation

This study investigated the use of ultra‐low‐pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes for water reuse applications where lower operating pressures and a high permeate quality are desired. A laboratory‐scale investigation was performed to compare the rejection and operational performance of RO, ULPRO, and NF membranes and to select two membranes for testing at a California water facility. A ULPRO membrane and an NF membrane were then tested at pilot and full scale at a water recycling plant and monitored for operational performance and rejection of total organic carbon, total nitrogen, and regulated and unregulated organic micropollutants. Pilot‐ and full‐scale testing of the best‐performing membranes demonstrated that both ULPRO and NF membranes could be used to meet potable water quality requirements. The presumed advantage of using ULPRO and NF membranes diminished as fouling occurred, resulting in operating pressures only slightly lower than or similar to those found for traditional RO membranes.

Beneficial use of co-produced water through membrane treatment: technical-economic assessment

Large amounts of co-produced water are generated during natural gas production. This study investigated the viability and cost effectiveness of ultra-low pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes as potential techniques for beneficial use of produced water by meeting potable and irrigation water quality standards and concentrating iodide in the brine. A 2-stage laboratory-scale membrane testing unit was employed to examine rejection of various constituents of concern at a low and high recovery using produced water generated from sandstone aquifers. The performance of two ULPRO membranes TFC-ULP (Koch) and TMG10 (Toray America) and one NF membrane NF-90 (Dow/Filmtec) was compared to a conventional RO membrane (TFC-HR, Koch). These membranes were pre-selected during previous bench-scale experiments with regard to specific flux, fouling propensity, salts and organics rejection, and iodide recovery efficiency. Of the membranes tested, the NF-90 achieved the highest specific flux. The salt rejection and iodide recovery by the NF-90, however, were much lower than the RO and ULPRO membranes tested. The permeate quality of the NF-90 met USEPA National Primary Drinking Water Standards, but exceeded the Secondary Standards regarding chloride and total dissolved salts. The two ULPRO membranes TMG10 and TFC-ULP, exhibited a higher specific flux as compared to the TFC-HR while displaying a similar rejection, notably the TMG10 which showed a very stable rejection at low and high recoveries. Cost analysis showed that the ULPRO membrane system provided marginally lower overall O&M costs than RO for meeting drinking water standards. The ULPRO membrane operation resulted in even lower treatment cost than RO and NF for meeting irrigation water standards, especially at high energy cost. Findings from these studies indicated that ULPRO membranes can provide a viable and cost-effective solution to beneficial use of produced water from sandstone aquifers.

Treatment of Acid Mine Drainage (AMD) by Ultra-Low-Pressure Reverse Osmosis and Nanofiltration

Secondary treatment of acid mine drainage (AMD) from a copper mine in China which has very low-concentration heavy metal ions and high conductivity (2,800 μs/cm), was attributed to the high concentration of dissolved monovalent and divalent ions. Commercially available polyamide ultra-low pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes were used to remove heavy metal ions and reclaim AMD. Effects of operation pressure, pH, temperature, water recovery efficiency, and operation time on ULPRO and NF performance were investigated. Experimental results show that the rejection increased with an increase of feed pressure and decreased with an increase of feed temperature, and it is dependent on feed pH. Generally, the rejections of heavy metal and total conductivity were greater than 97 and 96% for the ULPROM tested, respectively, which suggested the suitability of such membrane for AMD for the recovery of heavy metal and reclaiming wastewater. However, NF process was capable of removing about 90% of the heavy metals in the AMD and decreased 48% of the total conductivity.

Viability of nanofiltration and ultra-low pressure reverse osmosis membranes for multi-beneficial use of methane produced water

Produced water management has become one of the key factors to sustainable development of natural gas/oil resources. The substantial quantities of saline water present intractable environmental threats and also increase oil/gas production costs through produced water disposal such as deep well reinjection. Developing high-efficient and flexible treatment systems that can be operated at low costs is of high interests for producers and state regulators. Beneficial use of produced water could represent a new water resource especially for areas with inadequate existing supplies. Furthermore, some produced waters generated are also characterized by elevated concentrations of recoverable constituents, for example iodide. Recovering iodide from brine could offer additional benefits besides providing methane gas, reusing produced water, or reducing brine disposal volume. The advent of ultra-low pressure reverse osmosis (ULPRO) membranes and nanofiltration (NF) membranes with high desalting degree might offer a viable option for produced water treatment because these membranes can be as effective as reverse osmosis (RO) in removing certain solutes from water while requiring considerably less feed pressure resulting in lower operating costs. The objectives of this research were to investigate the viability of ULPRO and NF membranes as potential techniques to treat produced water by meeting water quality standards and concentrating iodide in the brine. The produced water extracted from sandstone aquifer in Eastern Montana was characterized as brackish groundwater of sodium chloride type with total dissolved solids (TDS) concentration of 5300 mg/L, absence of hydrocarbons, and average iodide concentrations of 55 mg/L. The produced water exhibited a very high potential to membrane fouling indicated by silt density index (SDI) measurements due to the presence of small particles and inorganic constituents. The studied candidate membranes included one RO membrane (TFC-HR, Koch Membrane Systems), three ULPRO membranes XLE (Dow/Filmtec), TFC-ULP (Koch) and TMG-10 (Toray America), and three NF membranes NF-90 (Dow/Filmtec), TFC-S (Koch), and ESNA (Hydranautics). Bench-scale cross-flow flat sheet test units were employed to assess the candidate membranes using the produced water with focus on fouling potential, iodide recovery, and general salt rejection. The degree of flux decline was found to be dependent upon the combination of permeate drag force and physico-chemical properties of the membranes. The membranes with higher permeability generally displayed faster initial flux decline. In addition, hydrophobic and rough membranes exhibited a higher flux decline and lower chemical cleaning efficiency than smooth and/or hydrophilic membranes. Flux decline experiments, in situ microscopic techniques, analysis of elemental composition and functional groups revealed that the pretreatment including microfiltration, pH adjustment and addition of antiscalants could alleviate membrane fouling significantly. Chemical cleaning using caustic and anionic surfactant solutions restored membrane permeability more efficiently than hydraulic cleaning or using acids and metal chelating agents. This study showed that TFC-ULP, TMG-10, and NF-90 membranes exhibited competitive efficiency regarding salt rejection, iodide recovery and adjusted specific flux as compared to a conventional RO membrane.

Effect of membrane fouling on transport of organic contaminants in NF/RO membrane applications

Commercial polyamide nanofiltration (NF), reverse osmosis (RO), and ultra-low pressure RO (ULPRO) membranes (NF-90, NF-200, TFC-HR, and XLE) as well as a cellulose triacetate RO membrane (CTA) were employed to investigate the effect of fouling on transport of organic micropollutants. Due to foulant precipitation and cake-layer formation, membrane surface characteristics changed considerably in terms of contact angle (an index of hydrophobicity), zeta-potential, functionality, and surface morphology, which potentially affected transport of contaminants as compared to unfouled (virgin) membranes. The transport of ionic organic micropollutants was hindered as a result of improved Donnan exclusion (electrostatic repulsion) likely due to a more negative surface charge as quantified by zeta-potential measurements. Membrane fouling also resulted in an increased adsorption capacity and reduced mass transport through partitioning and diffusion of solutes across the membrane. These effects led to an increase in rejection of hydrophobic non-ionic solutes (e.g., disinfection byproducts and chlorinated solvents) by fouled membranes. However, the increasing surface charge has the potential to result in a larger molecular weight cut-off of a fouled membrane due to membrane swelling, which can lead to lower rejection for hydrophilic non-ionic solutes, especially where nanofiltration membranes with a larger molecular weight cut-off are employed. Membrane fouling facilitated the transport of hydrophobic and hydrophilic organic contaminants through CTA membranes resulting in elevated concentrations of target solutes in the permeate. Findings of the study indicate that membrane fouling significantly affects the rejection of organic solute by CTA, NF, and ULPRO membranes while it is less important for thin film composite RO membranes.

CAN NANOFILTRATION AND ULTRA-LOW PRESSURE REVERSE OSMOSIS MEMBRANES REPLACE RO FOR THE REMOVAL OF ORGANIC MICROPOLLUTANTS, NUTRIENTS AND BULK ORGANIC CARBON? – A PILOT-SCALE INVESTIGATION

The scope of this project was to determine if low pressure membranes such as nanofiltration (NF) and ultra-low pressure reverse osmosis (ULPRO) membranes can meet water quality requirements necessary for indirect potable reuse while meeting acceptable operational parameters such as feed pressure, permeate flux, and flux decline. A total of 12 NF and ULPRO membranes were screened in this study and one ULPRO and one NF membrane were selected for a pilot-scale assessment (19 gpm) at a water reuse facility. Results of this study suggest that ULPRO and NF membranes can achieve similar removal efficiencies for the selected trace organics, nitrogen and bulk parameters tested as commonly employed RO membranes. While providing a similar water quality, these membranes can be operated at significantly lower feed pressures. These results suggest that ULPRO and NF membranes are viable for water reuse projects where a high permeate quality is required.

Rejection of Emerging Organic Micropollutants in Nanofiltration–Reverse Osmosis Membrane Applications

The rejection of emerging trace organics by a variety of commercial reverse osmosis (RO), nanofiltration (NF), and ultra-low-pressure RO (ULPRO) membranes was investigated using TFC-HR, NF-90, NF-200, TFC-SR2, and XLE spiral membrane elements (Koch Membrane Systems, Wilmington, Massachusetts) to simulate operational conditions for drinking-water treatment and wastewater reclamation. In general, the presence of effluent organic matter (EfOM) improved the rejection of ionic organics by tight NF and RO membranes, as compared to a type-II water matrix (adjusted by ionic strength and hardness), likely as a result of a decreased negatively charged membrane surface. Rejection of ionic pharmaceutical residues and pesticides exceeded 95% by NF-90, XLE, and TFC-HR membranes and was above 89% for the NF-200 membrane. Hydrophobic nonionic compounds, such as bromoform and chloroform, exhibited a high initial rejection, as a result of both hydrophobic-hydrophobic solute-membrane interactions and steric exclusion, but rejection decreased significantly after 10 hours of operation because of partitioning of solutes through the membranes. This resulted in a partial removal of disinfection byproducts by the RO membrane TFC-HR. In a type-II water matrix, the effect of increasing feed water recoveries on rejection of hydrophilic ionic and nonionic compounds was compound-dependent and not consistent for different membranes. The presence of EfOM, however, could neutralize the effect of hydrodynamic operating condition on rejection performance. The ULPRO and tight NF membranes were operated at lower feed pressure, as compared to the TFC-HR, and provided a product water quality similar to a conventional RO membrane, regarding trace organics of interest.

REJECTION OF EMERGING ORGANIC MICROPOLLUTANTS IN NANOFILTRATION/REVERSE OSMOSIS MEMBRANE APPLICATIONS

REJECTION OF EMERGING ORGANIC MICROPOLLUTANTS IN NANOFILTRATION/REVERSE OSMOSIS MEMBRANE APPLICATIONSThis study aimed to investigate factors affecting the rejection of emerging trace organics by a variety of commercial reverse osmosis (RO), nanofiltration (NF), and ultra-low pressure RO membranes during laboratory-scale experiments. Findings of this study indicated that rejection of negatively charged organics was driven by a combination of steric and electrostatic exclusion, which was...Author(s)Jörg E. DrewesPei XuChristopher BellonaGary AmyTae-Uk KimMark AdamThomas HebererSourceProceedings of the Water Environment FederationSubjectSession 1: AEESP Lecture and Fate, Transport and Treatment of Emerging Micro-PollutantsDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2004ISSN1938-6478SICI1938-6478(20040101)2004:16L.77;1-DOI10.2175/193864704784147548Volume / Issue2004 / 16Content sourceWEFTECFirst / last page(s)77 - 96Copyright2004Word count160

Rejection of organic compounds by ultra-low pressure reverse osmosis membrane

The introduction of ultra-low pressure reverse osmosis (ULPRO) membrane has widened the horizon of reverse osmosis (RO) in purification of surface water and wastewater as well as desalination of brackish water. The ULPRO membrane chemistry can provide a high water flux at low operating pressure, while maintaining a very good salt and organics rejection. This paper deals with the investigation on the rejection of low molecular weight organic compounds by ULPRO membrane. Laboratory scale experiments were carried out at a pressure of 3 kg/cm 2 with a feed flow rate of 1.20 l/min. The rejection of undissociated organic compounds did not show a close relationship with the feed pH. The percentage removal of undissociated organic compounds increased linearly with the molecular weight as well as with the molecular width. The removal efficiency can be predicted by these relationships. But neither molecular weight nor molecular width can be considered as an absolute factor for rejection. The feed pH also influenced the removal efficiency of dissociated organic compounds. The efficiency decreased linearly with the increase in the dissociation constant.

Application of ultra low pressure reverse osmosis (ULPRO) membrane to water and wastewater

There is a worldwide grave concern about water pollution control. To mitigate the water scarcity, in arid zones and in the areas with no other sources but brackish water, reverse osmosis technology has played an important role. In an effort to reduce the cost of energy requirement for RO operation, nanofiltration has been developed. Until recently the nanofiltration has been used in water softening and removal of disinfection byproduct (DBO). Use of nanofiltration to desalinate brackish water has been ruled out due to low rejection of salts. The introduction of ultra-low pressure reverse osmosis membrane, categorically a nanofiltration, has widened the horizon of using the nanofiltration in desalinating brackish water as well as surfacewater and wastewater. This development ensures the increase in flux due to improvement in active surface layer formation with the application of very small pressure. The surface charge and hydrophilicity on the surface material of the membrane have shown better flux stability in the high fouling conditions. With the addition of higher flux and higher rejection based on the same chemistry, ULPRO has made another step forward. This introduction will certainly reduce the operation cost and, more importantly, improve the overall reliability of the RO system. Application of nanofiltration is broadened to surface water treatment, wastewaters for nutrient removal and heavy metal rejection from wastewater.

A Cost Comparison of Potable Water Softening Technologies

Advances in membrane technology have yielded ultra low pressure reverse osmosis (ULPRO) systems as a potential water softening process. In order to establish the relative economic performance of such systems, they are compared directly with a number of alternative softening techniques through two case studies based on groundwater sites. Results suggest that although RO systems may not be the most cost effective for unblended peak load operation, they are likely to out perform alternative techniques for base load operation, and for base and peak load operations where high blending ratios are possible.