Low Pressure Reverse Osmosis Membrane Research Articles

Role of nanofiltration or reverse osmosis integrated to ultrafiltration-anaerobic membrane bioreactor treating vinasse for the conservation of water and nutrients in the ethanol industry

Sugarcane vinasse is the byproduct of ethanol production and, in many places, its final disposition has been its application in cane fields through fertigation. However, the incorrect practice of this technique can result in soil acidification, increase of salinity, and contamination of groundwater. Appropriate technologies and treatment processes can enable the recovery of byproducts from sugarcane vinasse, such as water, nutrients and energy. Thus, this study studied the integration of nanofiltration (NF) and reverse osmosis (RO), to ultrafiltration (UF) and two-stage anaerobic membrane bioreactor (2S-AnMBR) treatment aiming at the recovery of energy, nutrients (NF/RO concentrate) and water (NF/RO permeate). Seven types of commercial nanofiltration (NF) / reverse osmosis (RO) membranes were evaluated. The 2S-AnMBR reduced the vinasse organic matter and potentially produced 4.9 Nm3 of CH4 m−3 of vinasse that can be used for energy purposes. The low-pressure RO membrane stood out among the membranes investigated in this study, demonstrating a good performance in terms of pollutants retention, fouling potential and specific energy consumption (SEC), with an optimal recovery rate value below 40 % at 12 bar of operation. The final RO treatment was a viable alternative to generate water for industrial reuse, allowing the production of 3.2–4.8 m3 of treated water per m3 of ethanol produced. Besides, the retentate produced by RO had an organic carbon concentration 9 times lower compared to raw vinasse, which reduces the impact during soil disposal and associated CO2 generation.

A new technique to purify biologically treated wastewater by reverse osmosis: utilization of concentrate

Introduction. Possibilities to purify municipal wastewater using reverse osmosis membrane techniques are investigated aimed at production of quality water for industrial use or meeting regulations for surface water sources discharge. A new eveloped tools to utilize concentrate effluents by reducing its flow by a value that does not exceed 0.5–1.0 per cent of initial feed water flow and it’s withdrawal of all rejected impurities together with dewatered sludge as a sludge moisture. Objectives: development of reverse osmosis techniques to purify wastewater after biological treatment; evaluation of possibilities to radically reduce concentrate flow to withdraw it together with activated sludge as it’s moisture. 
 Materials and methods. Experimental research is conducted to develop membrane operational modes during wastewater treatment. Experimental procedure is developed and described to evaluate reduction of membrane rejection of dissolved impurities and product flow decrease during experimental wastewater treatment and concentrate utilization test run. 
 Results. The basic equations are derived that enable us to determine: the required concentrate flow value that corresponds to concentration values of COD and suspended solids values in the feed water; the required values of membrane recoveries that correspond to ammonia concentration in the feed water to meet required regulation values in the product water. The tools to evaluate membrane area and a number of membrane modules are developed and described. Optimum values of the working pressure are evaluated as well as other economic parameters are presented to compare the developed techniques with biological treatment.
 Conclusions. To reach the required ammonia concentration in product water, double stage treatment of feed water with low-pressure reverse osmosis membranes is required. Influence of dissolved organics defined as COD, on membrane performance. The optimum value of working pressure is determined which is 7.5–8 Bars.

A Highly Efficient Waste-Free Technology of Water and Fuel Preparation for Thermal Power Stations

A highly efficient, economical, and waste-free technology for the purification of natural waters for thermal power plants has been developed. The preliminary purification of water involved microfiltration on tubular ceramic membranes made of clay minerals according to a technology developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; the degree of retention of suspended solids and iron and manganese compounds on the membranes was 99.9, 99.8, and 60%, respectively. The high separation capacity of such membranes is due to the modification of their surface by water contaminants with the formation of a self-organizing dynamic membrane that serves as an additional barrier. The dynamic membrane formation contributed to the retention of up to 24.0% of the co-occurring ions, Ca2+ in particular; this is typical for ultrafiltration membranes. Further desalination was performed with low-pressure reverse osmosis membranes; two stages of reverse osmosis turned out necessary to achieve a total ion content of 0.5 mg/dm3 in the make-up water of a steam turbine unit of a thermal power plant (TPP). The retentate of the second stage of reverse osmosis, for which the total ion content is 50–60 mg/dm3, can be used for technical purposes at TPPs. The salt content of the retentate formed after the first stage of reverse osmosis was ~3 g/dm3, and thus insufficient for further transformation into secondary material resources; however, the introduction of waste recycling systems is considered to be the modern direction in protecting the environment from technological influence. The retentate of the first stage of reverse osmosis was concentrated using an original concentrating electrodialyzer developed at the Dumansky Institute of Colloid Chemistry and Water Chemistry, NAS of Ukraine; some design modifications that distinguish this electrodialyzer from the conventional ones were proposed and patented. Electrodialysis treatment of the retentate for 2.5 hours at a current density of 2.5 A/dm3 enabled the production of a solution with the ion content of ~105 g/dm3. This brine can be converted into sodium hypochlorite or caustic soda and hydrochloric acid by electrolysis. The diluate with a mineralization of ~200.5 g/dm3 and a total organic carbon content of ~148.3 g/dm3 can be used for the preparation of coal-water slurry fuels for power generation and metallurgy. The basic technological schemes of make-up water purification for the needs of thermal power plants and the preparation of slurry fuel systems based on coal and reverse osmosis waste that contains organic substances are proposed.

Surface modification of mesoporous silica nanoparticle with 4-triethoxysilylaniline to enhance seawater desalination properties of thin-film nanocomposite reverse osmosis membranes

Mesoporous silica nanoparticles (MSN), with higher water permeability than NaA zeolite, were used to fabricate thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. However, only aminoalkyl-modified MSN and low-pressure (less than 2.1 MPa) RO membrane were investigated. In this study, aminophenyl-modified MSN (AMSN) were synthesized and used to fabricate high-pressure (5.52 MPa) RO membranes. With the increasing of AMSN dosage, the crosslinking degree of the aromatic polyamide decreased, while the hydrophilicity of the membranes increased. The membrane morphology was maintained to show a ridge-and-valley structure, with only a slight increase in membrane surface roughness. At the optimum conditions (AMSN dosage of 0.25 g/L), when compared with the pure polyamide RO membrane, the water flux of the TFN RO membrane (55.67 L/m2/h) was increased by about 21.6%, while NaCl rejection (98.97%) was slightly decreased by only 0.29%. However, the water flux of the membranes was much lower than expected. We considered that the enhancement of RO membrane permeability is attributed to the reduction of the effective thickness of the PA layer.

A surrogate-based approach for trace organic chemical removal by a high-rejection reverse osmosis membrane

Public confidence in the safety of recycled water for potable water reuse can be improved by providing assurance regarding high removal of trace organic chemicals (TOrCs) by reverse osmosis (RO) treatment. This pilot-scale study assessed the effectiveness of a surrogate indicator—N-Nitrosodimethlyamine (NDMA)—for ensuring a high level of TOrC removal by a high-rejection RO membrane. The pilot-scale tests showed that the rejection of 23 TOrCs by the high-rejection RO membrane was consistently greater than NDMA rejection. In addition, NDMA rejection was highly correlated with TOrC rejection across varied operating conditions, indicating that NDMA can be used as a conservative surrogate indicator for TOrC removal. The RO treatment at a permeate flux of 20 L/m2 h and feed temperature of 13–27 °C resulted in as high as 75–87% NDMA rejection, which was considerably greater than a conventional low-pressure RO membrane (26–47%). However, the high-rejection RO membrane required a transmembrane pressure that was greater than that of the low-pressure RO membrane. Despite this disadvantage, this study suggests that the high-rejection RO membrane can effectively ensure a high level of TOrC removal (≥65%) when NDMA is used as a surrogate indicator, which cannot be ensured by assessing conventional conductivity rejection.

Development of low pressure reverse osmosis membrane for desalination process

Water shortage has become a real problem at global level and therefore, new and innovative technologies were established to provide sustainable solutions to water crisis. One of the effective approaches to resolve the global challenges is introducing the membrane-based desalination. Reverse Osmosis (RO) is a pressure driven membrane process which becoming increasingly popular and widely used for water purification applications that require high salt rejection such as brackish and seawater desalination. In this study, the influence of Sodium dodecyl sulphate (SDS) surfactant in producing the finest membrane for desalination were investigated in terms of performance, morphological structure and molecular orientation. From a polymer blending of polysulfone (PSF)/N-Methyl-2-Pyrrolidone (NMP)/polyvinylpyrrolidone (PVP)/sodium dodecyl sulphate (SDS) were formulated for making of low pressure reverse osmosis (LPRO) membrane. In order to examine the influence of SDS surfactant, different concentration from 0 wt% to 3 wt% were employed for desalination application of 10,000ppm (brackish water) and 50 000ppm (seawater). Experimental data showed that the increasing of 0.5wt% in surfactant produced higher pure water permeation (PWP) and flux. At 2.5wt% of SDS, the LPRO membranes showed the highest PWP of about 44.8L/m2h and brackish water flux at 45.58L/m2h. Meanwhile, at 3.0wt%, the highest flux of seawater at 39.37L/m2h was obtained. Moreover, the optimized LPRO (2wt% of SDS) membrane performed high rejection ratio of 90.9% for brackish water and 90.4% for seawater concentration of 10,000ppm and 50,000ppm, respectively. Therefore, the findings revealed that the fabricated LPRO membrane having a good potential to be used as eco-efficient desalination process of brackish water and seawater technology.

Development of Asymmetric Low Pressure Reverse Osmosis-Surfactants Membrane: Effect of Surfactant Types and Concentration

The effect of surfactants that are cationic (Cetyl trimethylammonium bromide (CTAB)), anionic (Sodium Dodecyl Sulphate (SDS)) and non-ionic (Triton X-100) on performance, morphologies and molecular orientation of Polysulfone (PSF) low pressure reverse osmosis (LPRO) membrane were addressed. The experimental data showed that the increasing of 0.5 wt% in surfactant concentration produced higher pure water permeation (PWP) and flux. At 2.5 wt% of SDS, the LPRO membranes achieved the highest PWP of about 64.42 L/m2 × h while 3.0 wt% of CTAB demonstrated the highest flux of 55.28 L/m2 × h. Analysis from morphological results foundthat the optimal performance at 89.6 % rejection was produced by the membrane with 2 wt% SDS which is a good promoter for the fine morphological structures of the membrane, thus producing fine spectrum of molecular orientation factor.

In Situ Modification of Reverse Osmosis Membrane Elements for Enhanced Removal of Multiple Micropollutants

Reverse osmosis (RO) membranes are widely used for desalination and water treatment. However, they insufficiently reject some small uncharged micropollutants, such as certain endocrine-disrupting, pharmaceutically active compounds and boric acid, increasingly present in water sources and wastewater. This study examines the feasibility of improving rejection of multiple micropollutants in commercial low-pressure RO membrane elements using concentration polarization- and surfactant-enhanced surface polymerization. Low-pressure membrane elements modified by grafting poly(glycidyl methacrylate) showed enhanced rejection of all tested solutes (model organic micropollutants, boric acid, and NaCl), with permeability somewhat reduced, but comparable with commercial brackish water RO membranes. The study demonstrates the potential and up-scalability of grafting as an in situ method for improving removal of various classes of organic and inorganic micropollutants and tuning performance in RO and other dense composite membranes for water purification.

Analysis of the Flux Performance of Different RO/NF Membranes in the Treatment of Agroindustrial Wastewater by Means of the Boundary Flux Theory.

Dynamic membrane system behaviour must be adequately addressed to avoid process unfeasibility. The lack of proper analysis will mean relying on erroneous permeate flux values in the system design, which will lead to quick and/or steady high fouling rates. In this paper, the authors present additional data supporting the boundary flux theory as a helpful tool for membrane engineers to carefully avoid process failures. By fitting the dynamic permeate flux data to the boundary flux model, it was possible to calculate the β fouling index for the three selected membranes (one nanofiltration (NF) and two reverse osmosis (RO) ones). The dynamic flux given by the low-pressure RO membrane did not follow sub-boundary operating conditions, since a sharp flux loss was measured throughout the whole operating cycle, pinpointing that supra-boundary flux conditions were governing the system. This was supported by the calculated value of the β fouling parameter, which resulted to be in the order of ten times higher for this membrane. However, the values of β→0 for the SC-RO and DK-NF ones, supported by the very low value of the sub-boundary fouling parameter α (0.002 and 0.007 L·h−1·m−2·bar−2, respectively), ensure nearly boundary operating conditions for these membranes.

Removal of polar organic micropollutants by pilot-scale reverse osmosis drinking water treatment

The robustness of reverse osmosis (RO) against polar organic micropollutants (MPs) was investigated in pilot-scale drinking water treatment. Experiments were carried in hypoxic conditions to treat a raw anaerobic riverbank filtrate spiked with a mixture of thirty model compounds. The chemicals were selected from scientific literature data based on their relevance for the quality of freshwater systems, RO permeate and drinking water. MPs passage and the influence of permeate flux were evaluated with a typical low-pressure RO membrane and quantified by liquid chromatography coupled to high-resolution mass spectrometry. A strong inverse correlation between size and passage of neutral hydrophilic compounds was observed. This correlation was weaker for moderately hydrophobic MPs. Anionic MPs displayed nearly no passage due to electrostatic repulsion with the negatively charged membrane surface, whereas breakthrough of small cationic MPs could be observed. The passage figures observed for the investigated set of MPs ranged from less than 1%–25%. Statistical analysis was performed to evaluate the relationship between physicochemical properties and passage. The effects of permeate flux were more pronounced for small neutral MPs, which displayed a higher passage after a pressure drop.

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.

Long-Term Stability of Low-Pressure Reverse Osmosis (RO) Membrane Operation—A Pilot Scale Study

Reverse osmosis (RO) elements operating at a low pressure (LP) or a low energy (LE) are generally called “LPRO” or “LERO”, and the nomenclature “LP” and “LE” are convertible due to the interrelated features of the pressure and the energy in the RO process. Not only can LPRO be operated at lower pressures, which enables energy saving, but also at the standard operating pressure with an enhanced permeate flux. In this study, the feasibility of the LPRO element was evaluated in the face of high fouling potential feed water. The commercially available standard RO and LPRO were chosen, and the membrane properties including the fouling susceptibility and the surface characteristics were thoroughly evaluated. The variations of various performance parameters were monitored during an 872 h operation in a pilot system, which was operated in a constant flux mode. Then, the used membranes were analyzed to further verify the fouling load localization and the fouling intensities. The average flux variation of the individual RO elements in a vessel and the economic feasibility of LPRO were also evaluated through a simulation study using an RO system design software. This study showed that the localization of fouling load within a pressure vessel of an LPRO system caused about 20% higher flux decline and almost 2-times higher salt passage than those of a standard RO membrane system. Furthermore, the simulation study predicted that average operating pressure difference ratio (%) between two RO membranes decreased from 24.4% to 17.8% and a substantial quantity of LPRO elements (83.3%) must be replaced to meet the designated water criteria only after 2 years’ operation.

Desalination and fouling of NF/low pressure RO membrane for shale gas fracturing flowback water treatment

Abstract Shale gas fracturing flowback water (SGFFW) generated during shale gas extraction is of great concern due to its high salinity and complicated components. In this study, the feasibility of nanofiltration (NF) and reverse osmosis (RO) for SGFFW desalination in assisting SGFFW reuse and discharge were systematically evaluated after the pretreatment of coagulation-ultrafiltration (UF) process. Under the same initial water flux of 1.27 × 10 −6 m/s, the water flux decreased tremendously within 800–1000 min for both NF(NF90) and low pressure RO(ESPA1) membranes. The stable water flux was only 38.2% and 15.8% of the initial water flux for NF90 and ESPA1 membrane, respectively. The removal efficiency of the Na + was 81.2% for NF90 membrane and 88.1% for ESPA1 membrane, while the rejection ratios of Cl − were 83.3% and 87.3% for NF90 and ESPA1 membrane, respectively. The rejection ratios for multivalent ions (i.e., Fe 3+ , Ca 2+ and Ba 2+ ) were typically very high (>90%). According to fluorescence regional integration (FRI) under the Excitation—Emission—Matrix Spectra (EEM) within each region volume, the dissolved organics removed by NF in different region decreased in the order of VI (86.0%), I (47.2%), III (31.8%), II (20.8%), V (6.2%), IV(0.2%), while the overall rejection ratio of RO decreased in the order of VI (100.0%), I (88.3%), II (70.7%), III (66.8%), V (58.9%), IV(0.3%). The difference in molecular weight(MW) distribution between the feed and permeate of NF/RO samples showed that the organics with MW of 20 kDa were greatly removed, indicating the NF/RO mainly intercepted this portion of organics such as guar gum, polyacrylamide and various surfactants. However, the effluent of the NF/RO still contained a large portion of biopolymers, which was plausible that small portion of polyacrylamide passed through the membrane. The elemental analysis by scanning electron microscope (SEM)-energy dispersive spectrometer (EDS) demonstrated the fouling layer was mainly composed of organics (i.e., polyacrylamide and aromatic protein). It seemed that developing new-type anti-fouling membrane was a feasible approach to decelerate the membrane fouling.

Effect of Coexisting Natural Organic Matters (NOM) on the Rejection of Endocrine Disrupting Chemicals (EDCs) by A Low Pressure Reverse Osmosis (LPRO) Membrane

The coexisting natural organic matters (NOM) in the water environment are expected to influence rejections of endocrine disrupting chemicals (EDCs) in membrane filtration. However, such influences and rejection mechanisms are not well understood. This paper aims to elucidate on the rejection of three representative EDCs: Bisphenol A (BPA), 17β–estradiol (E2) and 4–Nonylphenol (NP) by a LPRO membrane (UTC–60) with and without three representative NOM: humic acid (HA), fulvic acid (FA) and effluent organic matters (EfOM) in solutions by laboratory experiments. The EDCs rejections were enhanced with increasing solution pH and negative membrane zeta potential as a result of decreased membrane pore size. Adsorption of the EDCs on membrane surface and size exclusion were the most likely rejection mechanisms in absence of the NOM. Coexistence of the NOM in solutions, in general, enhanced the EDCs rejections. However, no specific trends in rejection were observed possibly due to diffusion of the adsorbed NOM and EDCs molecules through the membrane pores, physicochemical properties of the EDCs and several types of NOM molecules present in EfOM. The EDCs adsorption on NOM molecules and their adsorption on the membrane surface and/or retention by size exclusion were the most likely rejection mechanisms.

Fate of pharmaceuticals and their transformation products in integrated membrane systems for wastewater reclamation

The removal of pharmaceuticals (PhACs) present in urban wastewater by membrane bioreactors (MBRs) followed by reverse osmosis (RO) or nanofiltration (NF) membranes has been frequently addressed in the literature. However, data regarding the removal of their main human metabolites and transformation products (TPs) is still scarce. In this study, the presence of 13 PhACs and 20 of their metabolites and TPs was monitored during 2 consecutive years in the different treatment steps of urban raw wastewater (sewer, primary treatment, MBR and RO/NF). Rejection of the selected contaminants when using low pressure NF membranes (NF-90) or RO membranes (ESPA 2) after the MBR step was also investigated. The analgesic acetaminophen, which was found at the highest concentrations in the sewer and influent samples (18–74µgL−1) over the two experimental periods, was fully eliminated during MBR treatment. Those PhACs that were only partially removed after the MBR, were almost completely removed (>99%) by the RO membrane working under different process conditions. At a similar average permeate fluxes (18Lm−2h−1), the NF membrane showed high removal efficiencies (>90%) for all of the PhACs and their metabolites, though lower than those achieved by the RO membrane. When the flux of the NF90 membrane was increased to 30Lm−2h−1 (while still operating at a feed pressure lower than the RO membrane at 18Lm−2h−1) the performance of the membrane increased, achieving 98% rejection of PhACs.

Role of membrane and compound properties in affecting the rejection of pharmaceuticals by different RO/NF membranes

This study was conducted to assess the merits and limitations of various high-pressure membranes, tight nanofiltration (NF) membranes in particular, for the removal of trace organic compounds (TrOCs). The performance of a low-pressure reverse osmosis (LPRO) membrane (ESPA1), a tight NF membrane (NF90) and two loose NF membranes (HL and NF270) was compared for the rejection of 23 different pharmaceuticals (PhACs). Efforts were also devoted to understand the effect of adsorption on the rejection performance of each membrane. Difference in hydrogen bond formation potential (HFP) was taken into consideration. Results showed that NF90 performed similarly to ESPA1 with mean rejection higher than 95%. NF270 outperformed HL in terms of both water permeability and PhAC rejection higher than 90%. Electrostatic effects were more significant in PhAC rejection by loose NF membranes than tight NF and LPRO membranes. The adverse effect of adsorption on rejection by HL and ESPA1 was more substantial than NF270 and NF90, which could not be simply explained by the difference in membrane surface hydrophobicity, selective layer thickness or pore size. The HL membrane had a lower rejection of PhACs of higher hydrophobicity (log D>0) and higher HFP (>0.02). Nevertheless, the effects of PhAC hydrophobicity and HFP on rejection by ESPA1 could not be discerned. Poor rejection of certain PhACs could generally be explained by aspects of steric hindrance, electrostatic interactions and adsorption. High-pressure membranes like NF90 and NF270 have a high promise in TrOC removal from contaminated water.

The Pursuits of Ultimate Membrane Technology including Low Pressure Seawater Reverse Osmosis Membrane developed by “Mega-ton Water System” Project

Reverse osmosis (RO) technology has been widely applied to water treatment such as seawater desalination, and large RO plants are many in operation around the world. Moreover, much larger plants will be required to secure sufcient water resource in the near future because global water shortage and quality problems are still getting more serious. Mega-ton Water System project was carried out for sustainable management of water environment and for low-carbon path to develop advanced key technologies of water treatment. Lowpressure RO membrane for seawater desalination has been studied in the project as a part of the core technologies to realize mega plant that is capable of producing 1,000,000 m3 of freshwater per day. Fundamental and scientifc research for RO membranes based on fne structure analyses by means of transmission electron microscopy with a special technique was conducted, and practical tools for designing new innovative RO membrane were acquired by the structure analyses to quantify the physicochemical and chemical properties of RO membranes. As the result of studying on structural design of RO membrane, low pressure SWRO membrane was obtained to reduce energy consumption compared to conventional ones in the past of SWRO. The vision of the “Mega-ton Water System” is sustainable desalination and reclamation. The missions are: 1) energy reduction (20-30%), 2) water production cost reduction (50%), and 3) low environmental impact (fewer chemical operations). Water cycle in “Mega-ton Water System” is separated into two parts including i) Seawater RO (SWRO) system, and ii) Seawater RO system with PRO system. The main challenge of development goal is the construction of mega-ton-scale system for seawater desalination for half the current cost. Accordingly, we developed the world’s frst low-pressure, multi-stage, high yield RO system, using a low-pressure seawater desalination membrane, and as a result of incorporating into it the elemental technologies gained from research in subthemes, such as highly-efcient pressure energy recovery, low-cost and highly durable plastic piping, pretreatment without the use of chemicals.

Performances of nanofiltration and low pressure reverse osmosis membranes for desalination: characterization and modelling

The nanofiltration and the reverse osmosis processes are the most common techniques for the desalination of water contaminated by an excess of salts. In this present study, we were interested in the characterization of commercial, composite and asymmetric membranes of nanofiltration (NF90, NF270) and low pressure reverse osmosis (BW30LE). The two types of characterization that we opted for our study: (i) characterization of electrical proprieties, in terms of the surface charge of various membranes studied by the measurement of the streaming potential, (ii) hydrodynamic characterization in terms of hydraulic permeability with pure water, mass transfer and phenomenological parameters for each system membrane/salt using hydrodynamic approaches. The irreversible thermodynamics allowed us to model the observed retention Robs of salts (NaCl and Na2SO4) for the different membranes studied, to understand and to predict a good filtration with a membrane. A study was conducted on the type of mass transfer for each system membrane/salt: convection and diffusion. The results showed that all tested membranes are negatively charged for the solutions at neutral pH, this is explained by their material composition. The results also showed competitiveness between the different types of membranes. In view of that the NF remains effective in terms of selective retention with less energy consumption than LPRO.

Improvement of tap water quality for domestic use by membrane process

Nowadays, clean water supply demand is increasing day by day in Ho Chi Minh city (HCMC) due to the rapid increase of population. It has gained concerns about water supply management and improving tap water quality of domestic use. Moreover, the results achieved from laboratory analysis of those tap water samples did not comply with the water quality standard due to low pH, high hardness and high ammonia concentration. In order to improve the water quality, low pressure reverse osmosis membrane system was proposed to polish quality of tap water. The pollutant removal of membrane system analyzed on NO3--N, NH4+-N, total Fe, hardness and residue Cl- were 41 ± 17.6 %, 18 ± 16.9 %, 47 ± 26 %, 39 ± 6 % and 94 ± 6.9 %, respectively. The results show that the low-pressure reverse osmosis membrane could achieve effective improvement of water supply quality for domestic use and satisfy the demand of clean water in HCMC.

Treatment of Phenolic Wastewaters by a Domestic Low-Pressure Reverse Osmosis System

In this paper, the removal of phenol by using aqueous solution in a low pressure reverse osmosis membrane was investigated. The effect of feed pressure, feed concentration, feed flow rate and feed pH on phenol rejection was investigated. The results showed that feed pH is the most affective parameter on the phenol rejection. Rejection of phenol increased with increasing pH from 2 to 10 under the best conditions. According to the results, there was a critical pressure in this separation and for pressures higher than this pressure, phenol rejection decreased. Feed flow rate had a positive effect on the phenol rejection but the effect of feed concentration was similar to the effect of feed pressure. The results showed that the maximum rejection was measured equal to 71% at 200 mg/L, 408.1 kPa, pH =10 and 1.172 L/min feed flow rate.