Low Pressure Reverse Osmosis Research Articles

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.

Assessment of an integrated membrane system for surface water treatment

With the promulgation of more stringent regulations to guarantee that the drinking water presents minimal health risks, nanofiltration (NF) and low pressure reverse osmosis membrane (RO) processes are nowadays considered for surface water treatment. However, NF and RO spiral wound membranes are sensitive to fouling and an advanced pretreatment such as conventional train, microfiltration (MF) and ultrafiltration (UF) may be necessary to control productivity. Consequently, a study was undertaken to evaluate the efficiency of the combined processes, know as Integrated Membrane Systems, for surface water treatment. Two IMS were evaluated on polluted low salinity water: UF and conventional train prior low fouling reverse-osmosis membranes (LFRO). The one-year study has revealed the efficiency of the IMSs for surface treatment. Both IMSs tested produced water quality that exceeded the most stringent water quality proposed in the new European Directives. However, in case of blending with the pretreated water for remineralization, clarified water has to be disinfected due to its low microorganism removal. In term of hydraulic performances both pretreatments: UF and clarification were found to be effective to control RO fouling. Despite UF reduces the SDI well below the maximum advised by the membrane manufacturer, a slight fouling occurred on the RO membranes at high flux. Organic material plays a role in membrane fouling and therefore reducing SDI may not guarantee a low fouling rate of the RO membranes. Preliminary cost estimation is on-going in order to identify the water cost for both IMSs based on similar final water quality.

Reduction of water consumption and wastewater quantities in the food industry by water recycling using membrane processes

Due to the rising costs for fresh and wastewater, the treatment and reuse of low-contaminated process water streams from food processing companies is increasingly gaining in importance. In this study it was shown that water for reuse could be produced from this water by a specific treatment using membrane processes while achieving reduction of water consumption and wastewater quantities. Three examples of low-contaminated wastewater will be discussed: firstly a vapour condensate from milk processing, secondly chiller shower water from the meat processing industry and thirdly wash water from bottle washing machines. Due to the promising laboratory and pilot-scale experimental results, a demonstration plant with a capacity of 1–2m 3/h, consisting of the following stages, was set up: pretreatment; main treatment — 1st nanofiltration stage; post-treatment — 2nd nanofiltration or low-pressure reverse osmosis stage and UV water disinfection. Economical water treatment was possible in all three examples. The treated low-contaminated process water from chiller showers or bottle washing machines was of drinking quality and therefore suitable for reuse. After treatment, the vapour condensate could be reused as boiler make-up water which is subject to higher standards than drinking water. The experimental technology underwent an authorization procedure at the Saarland Ministry for Health, Germany, and was granted approval.

Low pressure reverse osmosis performances of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) thin film composite membranes: effect of coating conditions and molecular weight of polymer

Thin film composite (TFC) membranes with sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) as the top layer coated on ultrafiltration (UF) membranes were prepared under different preparation conditions including the polymer concentration, solvent used in the coating solution, drying temperature, and the polymer molecular weight. Membrane performances for nanofiltration that separated electrolytes such as MgSO 4 and NaCl from aqueous solution were investigated using the composite membranes thus prepared. The concentration of SPPO both in H +-form and in Na +-form showed different tendencies for MgSO 4 separation while it did not affect the separation of NaCl. Membrane permeation rate increased on increasing the molecular weight of the glycol ethers used as the solvent without sacrificing separation. TFC membranes prepared from high molecular weight SPPO exhibited better performances as compared to those prepared from lower molecular weight SPPO.

Identification of surface chemical functional groups correlated to failure of reverse osmosis polymeric membranes

The goal of this study is to identify the causes of membrane failure observed during a 15-month operation of a low pressure reverse osmosis (RO) membrane pilot plant to treat a highly organic surface water from the Hillsborough River in Tampa, Florida, using various surface analytical techniques. Three different commercial RO membranes, made of cellulose acetate or polyamide, were used in this pilot study, and all of these membranes showed performance deterioration presumably due to membrane fouling and degradation at given experimental conditions. In order to elucidate the mechanisms of membrane failure, scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were performed on the surface of the polymeric RO membranes used. More specifically, molecular composition including surface functional groups were identified from XPS analysis, confirmed by FTIR, and correlated to membrane failure. In addition, surface morphology and fouling layer composition were determined by SEM/EDS. The results indicated that the cellulose acetate membrane was biologically damaged, while the polyamide membrane was compromised by chlorine oxidation. The biodegradation of cellulose acetate was evidenced by the presence of nitrogen on XPS and FTIR scans. Chlorine uptake shown in XPS and FTIR scans of used polyamide membranes was a good indicator of chemical degradation. This study demonstrated that XPS, combined with FTIR and SEM/EDS, is a valuable diagnostic tool for failure analysis of polymeric RO membranes and provides valuable information to aid the manufacturers in designing better membranes for reverse osmosis.

Pilot-scale membrane bioreactor and reverse osmosis studies for direct reuse of secondary textile effluents

Post-treatment of secondary wastewater (80% textile, 20% municipal) was tested on a pilot scale low-pressure reverse osmosis (RO) module, to produce a polished effluent to be recycled into the textile factories. Two different flow sheets were used. In the first one, the feed to the RO was pre-treated in a coagulation and filtration unit. In the second one, a ZenoGem® membrrane hollow fibre reactor was used to separate the activated sludge from the permeate which was fed to the RO module. Experimental results are discussed as well as advantages and disadvantages of the two alternatives.

New chlorine-resistant polyamide reverse osmosis membrane with hollow fiber configuration

New asymmetric hollow fiber reverse osmosis (RO) membrane was developed from a new chlorine-resistant copolyamide [4T-PIP(30)] with a piperazine moiety by a conventional phase-separation method. The new 4T-PIP(30) hollow fiber membrane has the same low-pressure RO performance as cellulose triacetate hollow fiber membrane (FR = 205 L/m2 day, Rj = 99.6%) and superior chlorine resistance as well as pH resistance to conventional aramid RO membranes. Structural analysis and viscoelastic study revealed that the new hollow fiber consisted of a top skin, dense layer, and microporous layer, and that it began to decrease its elasticity at 80°C in water, which is possibly related to its good and stable RO performance around room temperature. Several kinds of RO modules were made from the new hollow fiber membranes, for which RO performances were stable for 2 years in chlorinated feed water desalination (the free residual chlorine ranged from 0.l to 1.1 mg/L). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 517–527, 2001

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.

Membrane Treatment of Secondary Textile Effluents for Direct Reuse

Post-treatment of secondary textile wastewater was tested at pilot scale on membrane modules (microfiltration MF, nanofiltration NF and reverse osmosis RO) for the direct reuse of polished effluent within the dyeing processes. The main polluting parameters monitored in the post-treatment were: organic compounds (COD), colour, surfactants and salinity (as conductivity). The first treatment scheme was made of ceramic MF followed by NF. Aluminium polychloride was added at high concentrations (of the order of 70 mg Al/L) to avoid MF membrane fouling. The quality of the final permeate, produced by NF fed on the MF permeate, was acceptable for water reuse. Clariflocculation (CF) plus multimedia filtration (MMF) followed by low-pressure RO was also tested. This process performed quite well: the RO module (p = 4 bar) ran for relatively long cycles (up to 80 hours) with 5% reduction of the permeate flow rate at a 10 L m−2 h−1 fluxes. A techno-economical analysis on the experimental data indicate that a high quality effluent (COD < 10 mg/l; conductivity < 40 μS/cm; negligible residual colour), to be recycled in the textile dyeing industry, may be produced at affordable costs (less than 0.25 ECU) from secondary textile wastewater.

Removal of oil pollutants in seawater as pretreatment of reverse osmosis desalination process

Weathered oil contaminated seawater (WOCS) was used to investigate the behavior of soluble oil components in seawater in various pretreatment processes for removal of oil pollutants in seawater. The various pretreatment processes were a reverse osmosis desalination process in combination with advanced oxidation processes, ultrafiltration, coagulation, GAC adsorption, biological treatment and separation with a low pressure RO membrane. WOCS was prepared by mixing oil, nutrients and fresh seawater which was exposed to sunlight to simulate photooxidation and microbial degradation of oil in the marine environment. It was found that WOCS contained soluble components with relatively small molecular size, which are refractory to biodegradation and difficultly removed by advanced oxidation processes (AOPs), UF membrane or coagulation using FeCl 3 or PAC as flocculants. However, DOC in WOCS (OCWOCS) was easily adsorbed to GAC. Low pressure RO membranes with higher salt rejection rate could remove more OCWOCS compared to those with lower salt rejection rate.

Membrane treatment of secondary textile effluents for direct reuse

Post-treatment of secondary textile wastewater was tested at pilot scale on membrane modules (microfiltration MF, nanofiltration NF and reverse osmosis RO) for the direct reuse of polished effluent within the dyeing processes. The main polluting parameters monitored in the post-treatment were: organic compounds (COD), colour, surfactants and salinity (as conductivity).The first treatment scheme was made of ceramic MF followed by NF. Aluminium polychloride was added at high concentrations (of the order of 70 mg Al/L) to avoid MF membrane fouling. The quality of the final permeate, produced by NF fed on the MF permeate, was acceptable for water reuse.Clariflocculation (CF) plus multimedia filtration (MMF) followed by low-pressure RO was also tested. This process performed quite well: the RO module (p = 4 bar) ran for relatively long cycles (up to 80 hours) with 5% reduction of the permeate flow rate at a 10 L m−2 h−1 fluxes.A techno-economical analysis on the experimental data indicate that a high quality effluent (COD < 10 mg/l; conductivity < 40 µS/cm; negligible residual colour), to be recycled in the textile dyeing industry, may be produced at affordable costs (less than 0.25 ECU) from secondary textile wastewater.

Integrated multi-objective membrane systems for surface water treatment: pretreatment of reverse osmosis by conventional treatment and ultrafiltration

Within the scope of this project funded by AWWARF and USEPA three very promising IMS's were identified for surface water treatment. This paper will cover some highlights of the research carried out by the Water Supply Company of North Holland and Kiwa on the combination ultrafiltration/ultra low pressure reverse osmosis. Productivity of the ultrafiltration proved to be stable for the first 6000 h. Then, at the end of summer, the backwash regime was not able to prevent accumulation of biofouling. This biofouling coincides with an increase in bacterial counts in the ultrafiltrate. Also the ultra low pressure reverse osmosis unit showed no significant fouling up to 6000 hours. Then a rapid decrease of the second stage MTC started caused by BaSO 4 precipitation, coinciding with an increase in feed-concentrate pressure drop caused by a severe biofouling. Ultrafiltration reduced the indicator organisms E.coli and spores of sulphite reducing Clostridia to under the detection limit. To determine the elimination capacity the feed of UF and ULPRO were spiked with MS-2 phages. Generally UF showed a complete (>5 log) removal. Once only a 2.7 log removal was found caused by defects in UF-membranes. ULPRO showed a high (4.7–4.9 log) although no complete removal. The results show that integrity measurement and monitoring of both membrane steps are essential. UF-integrity is measured by a pressure hold test and monitored by particle counting. Integrity of ULPRO is measured by vacuum testing and monitored by in situ conductivity measurement and particle counting. ULPRO gives a very high precursor removal. Potential measurements (24 h, 20°C, 1–2 mg/l Cl 2-residual) showed >95% removal of THMFP and HAAFP. IMS with UF and ULPRO are exceptional tools for control of microbials and DBP-precursors. Crucial for application may be control of biofouling in the system.

Integrated multi-objective membrane systems application of reverse osmosis at the Amsterdam Water Supply

Within the scope of a project funded by AWWARF and USEPA three very promising IMS's were identified for surface water treatment. This paper will cover some highlights of the research carried out by Amsterdam Water Supply (AWS) and Kiwa on the combination of biological activated carbon filtration, slow sand filtration and (ultra low pressure) reverse osmosis. Primary objectives of this IMS study are restriction of (bio)fouling, productivity control, disinfection and removal of DBP-precursors. To prevent fouling two pretreatment schemes were tested. The reference scheme consisting of coagulation, sedimentation, rapid sand filtration and slow sand filtration lowered the MFI to 2 s/l 2. The alternative scheme consisting of the reference scheme extended with ozonation and biological activated carbon filtration before slow sand filtration lowered the MFI to 1 s/l 2. Biofouling was characterized by AOC and biofilm formation rate. Average AOC values were low (<10 μg/l) and the biofilm formation rates were lower than the standard for biologically stable drinking water. After 9 months of operation no significant membrane fouling was observed. For both pretreatments only a slight flux decline was observed during a period of nine months of operation. No significant increase in pressure drop was observed. After an initial flux decline during the first two months for both pretreatments only little flux decline occurred. The flux of the RO pretreated with only slow sand filtration (reference scheme) still showed a (small) decline after the nine months test period. After the initial flux decline, the RO with extended pretreatment consisting of an additional ozonation and biological activated carbon filtration (alternative scheme) operated at a nearly constant MTC. Disinfection and integrity were tested by MS2 phage spiking resulting in a removal capacity of 3.4 log units. Because of their larger size the removal of other micro-organisms should be at least equal. However, with direct cell counts and heterotrophic plate counts a lower efficiency was found. This might be due to regrowth in the RO installation on the permeate side. The DBP-precursor content after both pretreatments was low. The Cl 2 demand for the reference scheme was twice as high as the Cl 2 demand for the alternative scheme. The DBP-precursor content in the permeate of both treatments was below the detection limit. It is concluded that the IMS at Leiduin is reliable. Fouling is manageable and productivity is nearly constant. The dosing of MS2 phages shows an acceptable removal. DBP-precursors are removed to below the detection limits by the ultra low pressure membranes.

Water reclamation from municipal wastewater using combined microfiltration-reverse osmosis (ME-RO): Preliminary performance data and microbiological aspects of system operation

Hollow fibre microfiltration (MF) was used as a pretreatment to reverse osmosis (RO) for evaluation of the production of high-quality water from secondary effluent. Four different low operating pressure RO membranes (PVD, CTA, TFCL and NF45) produced a target flux of 20 L/m 2h at the relatively low operating pressures of 230 kPa, 750 kPa, 550 kPa and 360 kPa, respectively. Conductivity measurements revealed rejections of ionic species of 99.2% and 41% for TFCL and NF45, respectively. TFCL and NF45 totally removed orthophosphates from microfiltered secondary effluent, but nitrite/nitrate were only partially removed. PVD and NF 45 were exposed to microfiltered secondary effluent in stirred cells for up to 4 d for detailed evaluation of bioadhesion. Bacteria rapidly attached and grew on these membranes and produced significant amounts of extracellular polymers. Adhesion of these organisms was random on some membranes, but aggregates were observed on others. The numbers of bacteria on the surfaces of the RO membranes began to diminish after 72h incubation in microfiltered secondary effluent. Three different primary colonizing microbes were isolated from membrane surfaces, two of which were tentatively assigned to the genus Pseudomonas.

Innovative design of nano- and ultrafiltration plants

The productivity of nanofiltration plants can be significantly improved by installing a reduced number of membrane elements serially in pressure vessels [1]. A reduced number of elements per pressure vessel results in a reduction of the hydraulic pressure losses, but more pressure vessels (with a shorter length) have to be applied. The water supply companies Friesland (WLF), Oost-Brabant (WOB) and the consultant DHV Water have developed a new pressure vessel and interconnector for nanofiltration and ultra low pressure reverse osmosis plants. This new pressure vessel in combination with the new interconnector allows optimization of the system hydraulics, without the need for extra pressure vessels. Compared to a traditional design with 6 elements serially placed in pressure vessels, an annual cost reduction of approximately 10–15% for membranes and pressure vessels can be achieved with the new design. In ultrafiltration plants, pressure vessels contribute to approximately 4% of the total construction costs. Since pressure vessels are principally not needed for pressure hold because of the low feed pressures applied, the pressure vessels can be replaced by the new interconnectors. Approximately 2% of the total construction costs can be saved in this way. Water supply company Friesland applies the new pressure vessel in an ultra low pressure reverse osmosis plant, that is started-up this year. Water supply company Oost-Brabant is testing the new interconnector for application in ultrafiltration plants.

Anglian Water membrane hybrid system for the soft drinks industry

This paper examines the general technical aspects of membrane technology when applied to the soft drinks industry. A full scale plant has been installed at Wells Soft Drinks in Northampton, the site is fed from a surface water source within the Anglian Water region. The new water treatment plant installed at Wells Soft Drinks was supplied and commissioned by Anglian Water in 1997. It is a Membrane Hybrid System. Developed by Anglian Water Innovation in the UK, the Membrane Hybrid System is a combination of ultrafiltration and reverse osmosis equipped with spiral wound ultra low pressure reverse osmosis thin film composite membranes and spiral wound ultrafiltration membranes (see Fig.1). For water treatment within the soft drinks industry, membrane applications have many advantages over the conventional ion exchange plants used in the industry.

Development of boron reduction system for sea water desalination

Since boron has been showing to induce male reproductive impediments in laboratory animals, the 1993 WHO guidelines for drinking water quality set the recommended guideline value at 0.3 mg boron/l based on the NOEL (no-observed-adverse-effect level). Since boron is not effectively removed by the conventional water treatment not only for drinking water and domestic wastewater treatment, the concentration in ambient water as well as drinking water is affected by its consumption such as for soaps and detergents in the catchment area. Boron is also affected by leaching from the surrounding geology, drinking water derived water sources affected by a weak alkali spring contains high level of boron. Since the rejection ratio of boron is extremely less than that of salts in RO membrane system applying to drinking water supply in the areas where scarce a fresh water resources, desalinated water contains higher level of boron than that of WHO drinking water quality guidelines. In order to develop of boron treatment system either fresh water or desalinated water, multi stage RO membrane treatment system has studied by using a pilot plant. The boron rejection of RO membrane depends greatly upon pH and driving pressure of RO process. However, the boron rejection does not depends upon its concentration of raw water. Therefore, it is necessary to apply multi stage RO membrane treatment system for producing a finished water that meets the WHO drinking water quality guideline level of boron. Since the secondary and third RO membrane treat less dissolved salt concentration such as observed in fresh water, the driving pressure of RO process for removing boron can operate at low pressure such as about 0.6 to 1.3 MPa. Therefore, multi stage RO membrane sea desalination process and a low pressure RO process can be recommendable for boron management with a reasonable additional cost in drinking water supply.

Performance of low pressure reverse osmosis membrane (LPROM) for separating mono- and divalent ions

This paper describes an investigation on the rejection of the divalent anions from ZnSO4 using LPROMs, and to establish the effect of operating pressure, feed concentration and temperature on metal removal, then to compare with the monovalent anions, ZnCl2. A bench-scale spiral wound configuration of sulphonated polysulphone low pressure reverse osmosis membrane (LPROM) was used to remove heavy metals at various operating conditions, i.e. operating conditions, solute concentrations and temperature. The results show that the higher the operating pressure the greater will be the permeate flux for heavy metals from both mono- and divalent anions. At low operating pressure however, metals from the divalent anions give a higher permeate flux than did the monovalent anions. Permeate flux in both mono- and divalent anions is shown to be subsequently increased by a decrease of the concentration of feed solution. Regarding metal removal, metals from divalent anions were rejected more effectively than monovalent anions at all levels of feed concentration.

Low-pressure reverse osmosis as a process for treatment of anionic pollutants in water environment

The recent development of new generation Low-Pressure Reverse Osmosis (LPRO) or nanofiltration membranes have received attraction for application in the field of wastewater and water treatment through an increasingly stringent regulation for drinking purpose and water reclamation. In this research, the application on treatment of anionic pollutants (NO3-, NO2-, Cl-, SO42- & H2PO4-) was done under very much lower pressure range of operation (0.49 to less than 0.1 MPa) than any other previous research has done. Moreover, the extended Nernst-Planck equation was used for analysis of the experimental data by considering effective charge density of the membranes.

Performance of low pressure reverse osmosis membrane (LPROM) for separating mono- and divalent ions

This paper describes an investigation on the rejection of the divalent anions from ZnSO4 using LPROMs, and to establish the effect of operating pressure, feed concentration and temperature on metal removal, then to compare with the monovalent anions, ZnCl2. A bench-scale spiral wound configuration of sulphonated polysulphone low pressure reverse osmosis membrane (LPROM) was used to remove heavy metals at various operating conditions, i.e. operating conditions, solute concentrations and temperature. The results show that the higher the operating pressure the greater will be the permeate flux for heavy metals from both mono- and divalent anions. At low operating pressure however, metals from the divalent anions give a higher permeate flux than did the monovalent anions. Permeate flux in both mono- and divalent anions is shown to be subsequently increased by a decrease of the concentration of feed solution. Regarding metal removal, metals from divalent anions were rejected more effectively than monovalent anions at all levels of feed concentration.