Low Pressure Reverse Osmosis Research Articles

Comparison of sand and membrane filtration as non-chemical pre-treatment strategies for pesticide removal with nanofiltration/low pressure reverse osmosis membranes

Pilot plant investigations of sand and membrane filtration (microfiltration (MF)/ultrafiltration (UF)/nanofiltration (NF)/low pressure reverse osmosis (LPRO)) have been performed to treat groundwater polluted with pesticides. The results show that simple treatment, with use of aeration and sand filtration or MF/UF membranes, does not remove pesticides. However, by reducing the content of key foulants, the techniques can be used as a pre-treatment for nanofiltration and low pressure reverse osmosis that has proved to be capable of removing pesticides. It was found that a lower fouling potential could be obtained by using the membranes, but that sand filter was better at removing manganese and dissolved organic matter. The results indicate that combining aeration, sand filtration and membrane techniques might be a good option for pesticide removal without any addition of chemicals and minimized membrane maintenance.

Brackish water desalination in the Algerian Sahara—Plant design considerations for optimal resource exploitation

A huge geothermal aquifer is located in the northern Algerian Sahara, with brackish water free from toxic inorganic compounds and organic matter. Therefore, this water is appropriate for good quality potable water production after partial desalination. This paper deals with the basic desalination plant design considerations in the context of overall optimal aquifer exploitation. The main types of criteria for such optimization are economic and environmental. Implementing the concept of “blending” reservoir water (at appropriate proportion) with desalinated water, allows cost-effective and environmentally attractive resource exploitation; the latter would be achieved by reinjecting the retentate (after desalination) free from any chemicals that may degrade the reservoir water quality by accumulation over the years. Results are summarized of a typical case study based on low pressure reverse osmosis (RO) membrane desalination. Key RO membrane performance data from a pilot unit are employed in support of this study. The results highlight the main features and the constraints in plant design and desalinated water recovery; constraints are mainly imposed by the need to avoid membrane scaling with no use of undesirable synthetic anti-scalants. The proposed cost-effective plant configuration and operating mode are in accord with the overall optimum resource exploitation. A cost analysis is also performed for a typical potable water production plant. Finally, possibilities are outlined of integrated exploitation of this geothermal reservoir, whereby energy is extracted in addition to potable water production.

Comparison of polyamide nanofiltration and low-pressure reverse osmosis membranes on As(III) rejection under various operational conditions

A nanofiltration (NF) membrane and a low-pressure reverse osmosis (LPRO) membrane both with aromatic polyamide selective layer from the same manufacturer were employed for the comparison of their performances in terms of As(III) rejection and filtration flux under a variety of operational conditions. In addition to the smaller membrane pore size, the LPRO membrane possesses much more dissociable functional groups than the NF membrane. When the feed pH was below the pKa1 value (9.22) of H3AsO3, for which the steric hindrance is the only rejection mechanism, the removal efficiencies by NF and LPRO were about 10% and 65%, respectively. When the feed pH was higher, for which electrostatic effect began to take effect, the removal efficiencies could reach 40% and 90% for NF and LPRO, respectively. The rejection performance of LPRO was marginally affected by the feed As(III) concentration or ionic strength, although ionic strength had a strong effect on the filtration flux. In contrast, feed As(III) concentration and ionic strength had little effect on the filtration flux but great influence on the As(III) rejection performance of NF. The filtration flux was enhanced with the increase of transmembrane pressure for either NF or LPRO. The NF model could predict the general trend of the effects of the filtration flux, the feed water chemistry and its own concentration on As(III) rejection ratio by the NF membrane, but the rejection ratios were over-predicted.

N-nitrosamine rejection by reverse osmosis: Effects of membrane exposure to chemical cleaning reagents

The impact of chemical cleaning on the removal of N-nitrosamines by low pressure reverse osmosis (RO) membranes was investigated. The results show that caustic chemical cleaning resulted in an increase in membrane permeability but caused a notable decrease in the rejection of N-nitrosamines. The impact of caustic chemical cleaning was particularly obvious for N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA), which have the lowest molecular weight amongst the N-nitrosamines investigated in this study. A correlation between the increase in permeability and the decrease in the rejection of either NDMA or NMEA could be observed. The rejection of conductivity also decreased as the membrane permeability increased, indicating that conductivity rejection can be an indicative parameter of predicting changes in NDMA and NMEA rejection during RO plant operation. The impact of caustic cleaning was not permanent and could be significantly reduced by a subsequent acidic cleaning step.

Application of low-pressure reverse osmosis for effective recovery of bisphenol A from aqueous wastes

In this study, bisphenol A (BPA) was removed from aqueous solutions using a low- pressure reverse osmosis system. The influence of various parameters such as feed pressure (136–544 kPa), feed flow rate (0.25–1.172 L/min), feed concentration (30–100 mg/L), and pH (8, 10, and 11) on BPA rejection was investigated. The results showed a maximum rejection of 87.34% for a 50 mg/L feed concentration at 408.1 kPa, pH 8, and 1.172 L/min feed flow rate. The effect of feed pressure on BPA rejection, showed a critical pressure at which the maximum rejection was observed. This critical pressure was measured to be in the range of 408–476 kPa. The most effective parameter on the BPA rejection was feed flow rate which showed a severe concentration polarization at the surface of the membrane. The effect of feed pH revealed a minimum rejection at pH 10.

Interfacial polymerization of polyamide-aluminosilicate SWNT nanocomposite membranes for reverse osmosis

A new method of single-pass flow which incorporates aluminosilicate single-walled nanotubes (SWNT) in a polyamide matrix was developed to fabricate thin film nanocomposite (TFN) membranes for low pressure reverse osmosis (RO) via interfacial polymerization. The TFN membranes were characterized using attenuated total reflectance–Fourier transform infrared (ATR–FTIR) and X-ray photoelectron spectroscopy (XPS) for the analysis of functional groups as well as composition of SWNTs. The typical morphology of polyamide layers was observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The introduction of SWNTs in polyamide active layer is evident with the proliferation of aluminum and silicon elements from XPS analysis. All membranes show the rugose structure with “leaf-like” outgrowths and the “ridge-and-valley” structure commonly observed in polyamide RO membranes. The hydrophilicity was increased as observed in the enhancement in water flux and pure water permeance, due to the presence of hydrophilic nanotubes. With the incorporation of the single-walled aluminosilicate nanotubes, higher permeate flux was achieved while sustaining high rejection of monovalent and divalent ions, typical of polyamide RO membrane.

Industrial water reclamation using polymeric membranes – case studies involving a car manufacturer and a beverage producer

This study presents the evaluation of different polymeric membranes for the reclamation of wastewater generated by two manufacturers. Specifically, ultrafiltration (UF) membranes were evaluated for wastewater pretreatment use while nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for wastewater reclamation use. Results show that both the UF membranes used were not suitable for pretreatment of the oily wastewater stream due to the presence of suspended cathodic electrodeposition (CED) paint particles. The CED paint particles rapidly deposit on the membrane surface resulting in severe fouling and very low permeate fluxes. With respect to the metals and beverage wastewater streams, the polyvinylidine-difluoride (PVDF) UF membrane was shown to be more suitable for pretreatment than the polyacrylonitrile UF membrane. The PVDF-UF membrane had relatively lower flux decline rates, higher turbidity and higher total organic carbon reduction rates. Meanwhile, the low-pressure RO membrane proved to be suitable for wastewater reclamation of the oily and beverage wastewater streams – showing low flux decline rates, high conductivity and high chemical oxygen demand reduction rates. In terms of reclaiming the metals wastewater stream, the NF membrane proved more suitable than the low-pressure RO membrane. The NF membrane had relatively higher permeate fluxes and metals rejection rates compared to the RO membrane.

Low-pressure reverse osmosis membrane separation of non-fluorinated and perfluorinated organic compounds in water

The purpose of this study is to compare retention characteristics of perfluorinated organic compounds (PFCs) and similar-structured non-fluorinated organic compounds (NFCs) by new generation low-pressure reverse osmosis (LPRO) membranes based on physicochemical properties of the compounds and the results of bench-scale membrane efficiency batch tests as the first-step screening. Molecular weight (MW), molecular size, and hydrophobicity of the compounds greatly influence their retentions by loose and low-desalting membranes than those by tight and high-desalting membranes. The retentions in general increased with increasing MW and molecular length (ML). The retentions are explained more reliably by using both MW and molecular width/height parameters. The roles of MW and ML on the retentions could not be differentiated, since MW increases almost linearly with ML. The NFCs are more easily rejected than the PFCs by the membranes most probably due to hydrophobic adsorption of the PFCs to membranes leading to their slippage through membrane pores owing to their slender molecular structures. Though retentions of NFCs and PFCs in their undissociated states are governed by steric/size exclusion mechanism, hydrophobic adsorption to membrane is a major event for PFCs while it is not for NFCs. Unlike NFCs, retentions of PFCs in their dissociated states are greatly enhanced due to overwhelmingly greater efficacy of electrostatic exclusion. This is the first study comparing retentions of NFCs and PFCs by LPRO membranes and is expected to serve as an important reference for further works.

Rejection of small and uncharged chemicals of emerging concern by reverse osmosis membranes: The role of free volume space within the active skin layer

Free-volume hole-radii of the active skin layer of one seawater and two low pressure reverse osmosis (RO) membranes – namely SWC5, ESPAB, and ESPA2 respectively – were evaluated using positron annihilation lifetime spectroscopy (PALS) with a slow positron beam. The results were related to the rejection of boric acid and eight N-nitrosamines to provide insights to the transport of these small solutes through RO membranes. At pH 8 (which is the experimental pH in this study), these solutes are uncharged. PALS analysis showed that the SWC5 has the smallest mean free-volume hole-radius (0.259nm) among the three RO membranes investigated here. Correspondingly, the SWC5 membrane exhibited the highest rejection of boric acid and all N-nitrosamines. Results reported here also showed that the rejection of these chemicals increased in the order of increasing molecular volume. In addition, the difference in their rejection amongst the three RO membranes investigated here was most apparent for those (i.e., boric acid and N-nitrosodimethylamine (NDMA)) with a small molecular volume. The EPSA2 and ESPAB were determined to have mean free-volume hole-radius of 0.289nm. However, the ESPAB membrane had lower water permeability and showed considerably higher rejection of boric acid and NDMA than the ESPA2 membrane. These results suggest that in addition to the mean free-volume hole-radius, other membrane parameters and properties such as the free-volume hole-radius distribution and thickness of the active skin layer can also play a role in governing the rejection of small and uncharged solutes by RO membranes.

Cleaning protocol for a FO membrane fouled in wastewater reuse

Forward osmosis (FO) is an emerging technology which can be applied in water reuse applications. Osmosis is a natural process that involves less energy consumption than reverse osmosis (RO), and therefore can be applied as a dilution process before low-pressure RO; it is expected to compete favourably against current advanced water reuse technologies that use microfiltration/ultrafiltration and RO. The focus of this research was to assess the efficiency of different cleaning procedures to remove fouling from the surface of a FO membrane during the operation of a submerged system working in FO-mode (active layer (AL) facing feed solution) intended for secondary wastewater effluent (SWWE) recovery, using seawater as draw solution (DS), which will be diluted and can further be fed to a low-pressure RO unit to produce fresh water. Natural organic matter (NOM) fouling was expected to affect the AL, while for the support layer (SL), transparent exopolymer particles (TEP) were used as indicators of fouling due to their stickiness and propensity to enhance the attachment of other foulants in seawater on the membrane surface. The composition of the NOM fouling layer was determined after proper characterisation with a liquid chromatograph coupled with organic carbon detection (LC–OCD), showing biopolymers and protein-like substances as the main constituents. NOM fouling showed high hydraulic reversibility after a 25% flux decline was observed, up to 89.5% when in situ air scouring for 15 min was used as a cleaning technique. Chemical cleaning with a mixture of Alconox, an industrial detergent containing phosphates, and sodium EDTA showed to increase the reversibility (93.6%). Osmotic backwash using a 4% NaCl solution and DI water proved to be ineffective to recover flux due to the salt diffusion phenomena occurring at the AL. Part of the flux that could not be recovered is attributable to TEP fouling on the SL, which forms clusters clearly identifiable with an optical microscope and TEP-specific dyeing/staining of the membrane. Two solutions were tested to clean in place of the SL: a 1% NaOCl solution and the same detergent solution used to clean the AL. The former agent compromised the integrity of the FO membrane, as proved with flux and conductivity measurements; 94.5% of flux was recovered with the latter agent, showing that chemically irreversible fouling for the FO membrane is on the order of 5.5%, which might be associated with the adsorption of biopolymers on the AL and some TEP residuals on the SL. Physical cleaning (air scouring) of the AL proved to be the most effective way to control fouling.

Study on vacuum membrane distillation of PP hollow fiber membranes used in concentrated seawater from low-pressure reverse osmosis

Concentrated seawater from low-pressure reverse osmosis (RO) was treated by membrane distillation technology (MD). Hydrophobic polypropylene (PP) hollow fiber was fabricated by the melt-spinning method. The microstructure of the PP hollow fiber membrane was observed. The effects of NaCl concentration, flow rate, and temperature on water flux and rejection rate were studied. The results showed that water flux and salt rejection rate changed a little with increasing initial concentration of NaCl solution. Water flux increased greatly with the increase in feed temperature, vacuum pressure and solution flow rate. The scanning electron microscopy (SEM) result indicated that the slit-like micropore size well formed with the maximal pore size 0.05μm wide while 0.3μm long. In this work, the maximal water flux reached 7.8 L/m2h, and the rejection ratio of NaCl was above 99.9%.

Purification of waters containing fluorine by low pressure reverse osmosis for their complex treatment

The paper has investigated main regularities of the purification process of brackish waters containing fluorine by low-pressure reverse osmosis. It has demonstrated high efficiency of the method with the use of a membrane of a TFC-75 brand. It has been established that chlorides have a negative influence on purification of the specified waters. We have proposed a technological flow chart for their complex processing using reverse osmosis.

Study on lithium separation from salt lake brines by nanofiltration (NF) and low pressure reverse osmosis (LPRO)

The aim of the present work is to study the separation of lithium from salt lake brines by NF and LPRO. NF90 membrane compared to the XLE a LPRO membrane appeared more efficient for Li+ extraction due to its higher hydraulic permeability to pure water and 0.1M NaCl solution, its lower critical pressure (Pc=0), its higher selectivity between monovalent ions (40%) obtained at low operating transmembrane pressure (below 15bar) and its lower average roughness (105±10nm) decreasing the propensity to be fouled. NF90 exhibited 100% rejection of magnesium in the first step separation from brine diluted ten times as 15% for Li+, with a final separation of 85% between Mg2+/Li+. The permeability to the diluted brine is 0.7L.h−1.m−2.bar−1 usable to size full scale experiments, but the fouling mechanism has to be discovered in the future work. In a second step we have not succeeded to separate totally Li+ and Na+ in the permeate obtained before (15% of separation only between Li+ and Na+). To solve this problem, we did dialysis. We obtained a total separation between Li+ and Na+ with a diffusion flux (4.42 10−7mol.s−1.m−2 at 20°C) for NaCl 0.1M 5 times higher for NF90 vs XLE.

Water purification of nitrates by low-pressure reverse osmosis method

The paper has investigated possibilities and basic regularities of water purification of nitrates by low pressure reverse osmosis. The negative influence of chlorides and sulfates on the process characteristic have bee shown. A conclusion has bee made on expediency of using the low pressure reverse osmosis method for purifying water of nitrates.

N-nitrosamine rejection by nanofiltration and reverse osmosis membranes: The importance of membrane characteristics

The influence of membrane characteristics on the rejection of eight N-nitrosamines was investigated using one nanofiltration (NF), one seawater reverse osmosis (SWRO) and six low pressure reverse osmosis (LPRO) membranes. The rejection of the two lowest molecular weight N-nitrosamines, namely N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA), varied in the range from 8–82% to 23–94%, respectively. In general, the rejection of NDMA and NMEA increased with decreasing membrane permeability. The impact of membrane characteristics became less important for higher molecular weight N-nitrosamines. Among the four LPRO membranes (i.e. ESPA2, LFC3, TFC-HR and 70LW) that are commonly used for water reclamation applications, similar rejections were obtained for NDMA (37–52%) and NMEA (69–82%). In addition, rejection values of NDMA and NMEA among two LPRO membranes (i.e. ESPA2 and 70LW) were almost identical when compared under variable permeate flux and feed temperature conditions. However, it is noteworthy that the ESPAB membrane could achieve very high rejection of NDMA (as high as 71%) despite having a similar permeability to the LPRO membranes. Results reported here suggest that membrane characteristics associated with permeability such as the pore size and thickness of the active skin layer can be a key factor determining N-nitrosamine rejection.

Potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus for aquaculture

Aquaculture activities in developing countries have raised deep concern about nutrient pollution, especially excess phosphorus in wastewater, which leads to eutrophication. NF, NF90, NF450 and XLE membranes were studied to forecast the potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus from aquaculture wastewater. Cross-sectional morphology, water contact angle, water permeability and zeta potential of these membranes were first examined. Membrane with higher porosity and greater hydrophilicity showed better permeability. Membrane samples also commonly exhibited high zeta potential value in the polyphosphate-rich solution. All the selected membranes removed more than 90% of polyphosphate from the concentrated feed (75 mg/L) at 12 bar. The separation performance of XLE membrane was well maintained at 94.6% even at low pressure. At low feed concentration, more than 70.0% of phosphorus rejection was achieved using XLE membrane. The formation of intermolecular bonds between polyphosphate and the acquired membranes probably had improved the removal of polyphosphate at high feed concentration. XLE membrane was further tested and its rejection of polyphosphate reduced with the decline of pH and the addition of ammonium nitrate.

Performance evaluation of reverse osmosis technology for selected antibiotics removal from synthetic pharmaceutical wastewater

This study addresses the possibility for low pressure reverse osmosis membrane (RE 2521, CSM) process to serve as an alternative to remove selected antibiotics (ampicillin and amoxicillin) from synthetic wastewater by changing operating conditions such as pH = 3, 6.5 and 10; Pressure = 9, 11 and13 (bar); antibiotic concentration = 10, 255 and 500(mg/L), and temperature = 20, 30 and 40°C. The experiment was designed based on Box-benken, which is a Response Surface methodology design (RSM), using Design Expert software. The concentration of antibiotics was measured by applying a UV-spectrophotometer (Cecil), at the wavelength of 254 nm. Results showed a range of rejection percentage from 73.52% to 99.36% and 75.1% to 98.8%, for amoxicillin and ampicillin, respectively. Considering the solute rejections and the membrane porosity show that the prevailing rejection mechanism of the examined antibiotics by the membrane was the size exclusion effect. The permeate flux for both of the antibiotics was 12–18.73 L/m2.h. Although the permeate flux and antibiotic rejection are influenced by operating pressure, pH, and temperature individually, the interaction between operating parameters did not have noticeable effects. According to the results obtained in this study, the application of RO membrane is recommended for the selected antibiotics to be removed to a considerable degree (up to 95%).

Evaluation of high productivity brackish desalination membrane

High productivity reverse osmosis membrane developed under the Office of Naval Research Expeditionary Unit Water Purification Program was evaluated at the Bureau of Reclamation Brackish Groundwater National Desalination Research Facility (BGNDRF). Performance of the new membrane was evaluated in comparison to two other commercial high productivity or low pressure reverse osmosis membranes using a high productivity test system designed and built to take best advantage of high flux membrane through either lower operating pressure or greater productivity. Membranes were evaluated with brackish groundwater over a range of cross flow velocities and recovery rates. Experimental membrane water transport was approximately twice two to three times that of the commercial membrane and salt transport was an order of magnitude less than commercial membrane at 20% recovery for three modules of four inches by forty inches in series tested at a range of feed flow rates.

Water defluoridation using nanofiltration vs. reverse osmosis: the first world unit, Thiadiaye (Senegal)

The possibility of producing drinking water from brackish groundwater polluted with F- using nanofiltration (NF) process was previously studied at a pilot scale. Brackish groundwaters were taken from the south of Morocco (Tan Tan city) and from the center west of Senegal (Thiadiaye City). The performances of few commercialized NF spiral wound elements, low-pressure reverse osmosis (LPRO), and reverse osmosis (RO) were compared to a large-scale pilot experiments (membrane area, 7.6 m2). The following parameters were determined: hydraulic permeability, total salinity; and Cl-, F-, and SO42- removals were compared under the influence of various experimental parameters such as flow yield ratio, transmembrane pressure, energy consumption and water compositions before and after treatment. This study shows that NF provides specific advantages for fluoride removal as compared to LPRO and RO. Indeed, NF permits to reduce partially the total salinity and to reject selectively fluorides with a high flow yield ratio, at low pressure (lower than 20 bars) and therefore with a low energy consumption as compared to actual RO membranes. Furthermore, this paper presents the first NF plant in the world dedicated to water defluoridation by nanofiltration and built recently in Thiadiaye (Senegal) (fresh water production 33,000 L/h).

Effects of feed solution characteristics on the rejection of N-nitrosamines by reverse osmosis membranes

Abstract The rejection of eight N-nitrosamines was investigated in this laboratory-scale study, focusing on the influence of feed solution characteristics on their separation by low pressure reverse osmosis membranes. The rejection mechanisms of N-nitrosamines were first examined using one nanofiltration (NF90) and two reverse osmosis (TFC-HR and SWC5) membranes. The TFC-HR membrane was used to investigate the effects of feed solution characteristics. The rejection of a particular N-nitrosamine was generally membrane dependent and increased in the order of NF (NF90), low pressure RO (TFC-HR) and seawater RO (SWC5) membranes. In general, the rejection of N-nitrosamines by a given membrane also increased in the order of increasing molecular weight. These results suggested that steric hindrance was a dominating rejection mechanism of N-nitrosamines. Nevertheless, it was also observed from the result of N-nitrosomorpholine (NMOR) that the rejection of N-nitrosamines may also depend on other physicochemical properties such as hydrophobicity. A decrease in the feed solution pH (from 9 to 3) resulted in a decrease in the rejection of the two smallest molecular weight N-nitrosamines, namely N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA). Changes in the feed solution ionic strength (from 26 to 260 mM) caused a discernible decrease only in NDMA rejection, while no apparent impact on rejection was observed for an increase in the feed concentration. On the other hand, it is striking that an increase in the feed temperature led to a significant decrease in the rejection of all N-nitrosamines and the impact was more pronounced for the small molecular weight N-nitrosamines. For example, a significant drop in NDMA rejection (from 49 to 25%) was observed as the feed temperature increased from 20 to 30 °C. The results also indicate that pH, ionic strength, and temperature of the feed solution can exert some influence on the rejection of NDMA and in some cases other N-nitrosamines. The combined effects of these feed solution characteristics, particularly feed temperature, may account for some of the variation of NDMA rejection by RO membranes previously reported in the literature.