Reverse Osmosis Spiral-wound Membranes Research Articles

Performance evaluation of pilot-scale reverse osmosis spiral wound membrane for water desalination systems

Abstract The increasing scarcity of potable water increases the demand for non-conventional potable water resources such as desalination. Experiments are carried out using a pilot-scale device of the desalination process for three configurations of membrane allocation inside the pressure vessel. Configuration (A) is one pressure vessel containing one spiral wound membrane (SWM), (B) is four pressure vessels each containing one SWM connected in parallel, and (C) is one pressure vessel containing four membranes connected in parallel. The effect of applied pressure, temperature, and water salinity is studied. Moreover, a mathematical model using ANSYS Fluent was developed and verified using the experimental data. The mathematical model is applied to an idealized case of an actual desalination plant. The main findings are (1) configurations (B) and (C) accomplished higher permeate discharge comparing to (A) by an average percentage of 60 and 50, respectively, while (C) has the lowest output salinity by 30% from configuration (A). (2) The mathematical model is found to reduce the operating pressure of the plant by 8%.

Understanding of surface fouling of brackish water reverse osmosis spiral wound membrane using an integrated analysis of seawater quality and membrane autopsy

To understand the cause of the scale, an integrated analysis of the saline water quality and discarded reverse osmosis membranes was developed. Damaged areas on the membrane were excised and characterized by the Fujiwara test, infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. A spatula and sonication were used to remove scale. Thermodynamic modeling (PHREEQC) was used to predict scale formation at 75 bar, resulting in saturation index values for both mixed and pure compounds. Fujiwara's test revealed damage to the polyamide and organic fouling by polysaccharides, silica, and aromatics. Thermo-oxidative decomposition and residual masses of metal oxides and salts were observed. The microscopy detected incrustations in the membrane by analyzing compounds with silicon, oxygen, calcium, magnesium, aluminum, etc. The modeling indicated the low-solubility compounds of scale are aluminum silicates, clays, quartz, etc., identified experimentally. PHREEQC can model desalination to predict scale problems, allowing for early decision-making.

ENVIRONMENTAL PROBLEMS CAUSED BY THE USE OF REVERSE OSMOSIS MEMBRANE ELEMENTS, AND WAYS TO SOLVE THEM

More than 70 percent of our planet is covered with water. And yet water is a scarce resource, and it is our future. According to the World Wildlife Fund, 1.1 billion people do not have access to it, and 2.7 billion experience a shortage of drinking water at least once a year. By 2025, two-thirds of the world's population may face water shortages. The shortage of drinking water and the search for renewable resources are of the most important problems in the modern world, the solution of which is directed to considerable intellectual and financial resources. Reverse osmosis is one of the most common technologies for obtaining high-quality drinking water. Technological solutions constantly improve the process of reverse osmosis and reverse osmosis spiral wound membrane elements used, science and business go hand in hand. But the price of this progress is the annual generation of a large amount of waste generated from used reverse osmosis roll membrane elements, which are usually sent to the landfill, while there are no technological solutions for their disposal. This work provides information on the available amount of such waste in the world and the dynamics of its growth in order to assess the scale of environmental damage that occurs as a result. The work collected information about the market of reverse osmosis spiral wound membrane elements in the world, and directions of their use. The structure, composition of components and technical characteristics of reverse osmosis spiral wound membrane elements are considered in detail, which makes it possible to evaluate the ways and possibilities of their utilization. The problems of surface contamination due to various types of fouling are considered. The main attention in the work is given to the reasons that cause the formation of waste. Based on the collected data, the scale of annual waste generation, which is formed due to spent reverse osmosis roll membrane elements, was analyzed. The possibility of reusing reverse osmosis spiral wound membrane elements and the main methods of their safe disposal are also considered. Summarizing the work carried out, recommendations were made on ways to solve the problem.

Deformation-induced cleaning of organically fouled membranes: Fundamentals and techno-economic assessment for spiral-wound membranes

Membrane fouling is a ubiquitous challenge in water treatment and desalination systems. Current reverse osmosis (RO) membrane cleaning technology relies on chemical processes, incurring considerable costs and generating waste streams. Here, we present a novel chemical-free membrane cleaning method applicable to commercially existing RO spiral-wound membrane modules. The method employs controlled membrane deformation through pressure modulation, which induces shear stresses at the foulant-membrane interface that lead to detachment and removal of the foulants. To investigate the effectiveness of the method, experiments on organic fouling by alginate are conducted on a flat-sheet membrane coupon followed by tests on a commercial spiral-wound module with feeds of varying fouling propensities. Cleaning durations are six-fold lower, and the experimental results demonstrate flux recoveries and cleaning efficiencies comparable to those of chemical cleaning. The experiments on the spiral-wound module indicate that this method will have applicability in industrially-relevant settings. To elucidate the underlying cleaning mechanisms, membrane deformation experiments with no flow are conducted, and in situ visualization techniques are employed for both the flat-sheet and spiral-wound modules. The results show that cleaning is caused by a reduction in shear strength at the foulant-membrane interface after cycles of repeated loading, a behavior typical of fatigue. By enabling more frequent cleanings, deformation-induced cleaning is shown to considerably lower operating costs in an economic case study while offering a more sustainable and environmentally sound solution to membrane cleaning and antifouling in desalination.

A time-dependent model of pressure drop in reverse osmosis spiral wound membrane modules

Abstract Reverse osmosis (RO) is the leading technology in desalination for both, brackish and seawater. Modeling RO process is a complex task as there are a high dependence on the operating conditions and feedwater characteristics. One of the main drawbacks of this technology is the performance decay due to fouling impact. Usually, fouling make the pressure drop to increase. This increase has not been reflected in the proposed models in RO process. The aim of this work was to proposed a time-dependent model for the pressure drop in RO process. For this purposes long-term experimental data of two full-scale brackish water RO desalination plants with two stages each were used. The first desalination plant was operating along 11 years in continuous regime while the second desalination plant was in operation during 14 years in intermittent regime. In the first desalination plant, the pressure drop ranges were 75-250 kPa and 25-150 kPa in the first and second stage respectively while in the second desalination plant were 50-200 kPa and 20-125 kPa. The behavior of the experimental data in both cases was close to an exponential function. The mentioned function was fitted in time domain using the standard deviation as error function.

Sacrificial coating development for biofouling control in membrane systems

Current cleaning strategies for biofouling control on spiral wound membrane systems used for seawater desalination are not effective and can hinder long-term membrane performance. To enable effective cleaning of a membrane, we examined the in-situ application and the use of a sacrificial multilayer polyelectrolyte coating on the membrane surface. The membrane coating was based on a layer-by-layer assembly approach using two non-toxic linkers, poly (diallyl-dimethyl ammonium chloride) and poly(sodium-4-styrene sulfonate). This polyelectrolyte coating was effectively applied on the membrane surface under cross-flow conditions, and it was stable on the membrane surface under continuous operation. Coating removal requires only a concentrated sodium chloride solution (synthetic brine in our study) adjusted to pH 11. Using this procedure, both the biofilm and the sacrificial layer could be simultaneously removed, leaving a clean surface compared to the non-coated membrane. Biofouling tests showed that the coated membrane had two-fold higher permeate flux recovery than the control non-coated membrane. The used polyelectrolyte sacrificial coatings avoided the use of toxic linkers and harsh cleaning chemicals, and thus it is a suitable technique for biofouling control on reverse osmosis spiral wound membranes.

Performance Assessment of SWRO Spiral-Wound Membrane Modules with Different Feed Spacer Dimensions

Reverse osmosis is the leading process in seawater desalination. However, it is still an energy intensive technology. Feed spacer geometry design is a key factor in reverse osmosis spiral wound membrane module performance. Correlations obtained from experimental work and computational fluid dynamics modeling were used in a computational tool to simulate the impact of different feed spacer geometries in seawater reverse osmosis spiral wound membrane modules with different permeability coefficients in pressure vessels with 6, 7 and 8 elements. The aim of this work was to carry out a comparative analysis of the effect of different feed spacer geometries in combination with the water and solute permeability coefficients on seawater reverse osmosis spiral wound membrane modules performance. The results showed a higher impact of feed spacer geometries in the membrane with the highest production (highest water permeability coefficient). It was also found that the impact of feed spacer geometry increased with the number of spiral wound membrane modules in series in the pressure vessel. Installation of different feed spacer geometries in reverse osmosis membranes depending on the operating conditions could improve the performance of seawater reverse osmosis systems in terms of energy consumption and permeate quality.

Investigation on hydrodynamics and mass transfer in a feed channel of a spiral-wound membrane element using response surface methodology

Using the response surface methodology (RSM) coupled with computational fluid dynamics, the hydrodynamic and mass transfer have been investigated in a spacer-filled channel. Geometry of an industrial reverse osmosis spiral-wound membrane module has been set to optimize the pressure drop, water permeation flux and the spacer configuration efficacy with respect to the average inlet velocity, the spacer attack angle and the spacer mesh angle. Several tools have been used to implement the response surface methodology: The Latin Hypercube Sampling Design method for design points generation, the Kriging model for interpolation and regression, and the genetic algorithm for optimization. It was found that the optimum configuration taking all the output operational parameters into account was stood up at the attack angle of 75°, the mesh angle of 85.9°, and the average inlet velocity of 0.0428m/s. Also the global sensitivity analysis has been performed, which the average inlet velocity and the attack angle were obtained the most and the least effective parameters on optimum conditions, respectively. Due to the change in the velocity along the RO module with several SWM elements, the optimum performance was achieved by adjusting the geometric structure of the spacers with velocity variations in each RO element.

Grey water treatment and simultaneous surfactant recovery using UF and RO process

ABSTRACTThe membrane-based grey water treatment for grey water reuse and surfactant recovery is presented in this research paper. Grey water from washing machine discharges having turbidity and used surfactant was processed through the polymeric ultrafiltration (UF) membrane to remove the turbidity. The UF treated grey water is further purified by reverse osmosis (RO) membrane for surfactant recovery and water reuse. The surfactant trapped inside the RO spiral wound membrane module is recovered through various membrane physical regeneration techniques such as backwashing, simultaneous backwash–back-flush and ozone back-flush. Among this, backwash–back-flush is found to be effective process for surfactant recovery. The methodology for optimising surfactant recovery is captured by studying effect of various operating parameters such as feed detergent concentration, backwash pressure, backwash temperature and back-flush flow rate. By implementing optimal process conditions, the integrated UF and RO membrane process is able to produce 300 L of reusable pure water and 80 L of concentrated detergent solution and 20 L of turbid water while treating 400 L of grey water discharges. Maximum surfactant recovery of 82% is obtained while treating grey water which consists of 720 ppm of total dissolved solids (detergent) and 45 ppm of surfactant. The extent of UF and RO membrane fouling is determined by measuring the pure water flux before and after the grey water treatment. The membrane performance is found to be stable when membrane is regenerated by backwash–back-flush technique for RO and gravity backwash for UF membrane.

Fouling of a spiral-wound reverse osmosis membrane processing swine wastewater: effect of cleaning procedure on fouling resistance

ABSTRACTSwine manure is a valuable source of nitrogen, phosphorus and potassium. After solid–liquid separation, the resulting swine wastewater can be concentrated by reverse osmosis (RO) to produce a nitrogen–potassium rich fertilizer. However, swine wastewater has a high fouling potential and an efficient cleaning strategy is required. In this study, a semi-commercial farm scale RO spiral-wound membrane unit was fouled while processing larger volumes of swine wastewater during realistic cyclic operations over a 9-week period. Membrane cleaning was performed daily. Three different cleaning solutions, containing SDS, SDS+EDTA and NaOH were compared. About 99% of the fouling resistance could be removed by rinsing the membrane with water. Flux recoveries (FRs) above 98% were achieved for all the three cleaning solutions after cleaning. No significant differences in FR were found between the cleaning solutions. The NaOH solution thus is a good economical option for cleaning RO spiral-wound membranes fouled with swine wastewater. Soaking the membrane for 3 days in permeate water at the end of each week further improved the FR. Furthermore, a fouling resistance model for predicting the fouling rate, permeate flux decay and cleaning cycle periods based on processing time and swine wastewater conductivity was developed.

Membrane filtration of the liquid fraction from a solid–liquid separator for swine manure using a cationic polymer as flocculating agent

The liquid fraction from a solid–liquid separator for swine manure, which used a cationic polymer to promote particle flocculation, was processed by one nanofiltration and two reverse osmosis spiral-wound membranes. Eight different liquid fraction batches (750 to 1750 L) were concentrated at volumetric concentration ratios (VCRs, initial to final volumes) ranging from 2.3 to 4.2. Membrane fouling intensity was highly variable, as water flux recovery after concentration cycles ranged from 13% to 88%. The most severe fouling was caused by a liquid fraction that had relatively low suspended solids (SS) (774 mg/L) and was concentrated at a low VCR of 2.6. Raw manure collected the same day also contained low SS, suggesting that fewer sites were available for polymer adsorption and thus more polymer remained in the liquid. However, because of the high opacity of the samples, residual polymer could not be detected in any feed or concentrate samples. Fouling was not totally irreversible as over 97% of membrane flux could be recovered by cleaning with acidic and alkaline solutions. Further tests with spiked liquid fractions indicated that fouling due to residual polymer in solution started to occur at a polymer concentration of 3 and 11 mg/L in initial and concentrated effluents, respectively. If a cationic polymer is used to pretreat manure, the amount of added polymer would have to be closely related to SS content as opposed to manure volume, in order to leave very little residual polymer in solution.

The potential of standard and modified feed spacers for biofouling control

Abstract The impact of feed spacers on initial feed channel pressure (FCP) drop, FCP increase and biomass accumulation has been studied in membrane fouling simulators using feed spacers applied in commercially available nanofiltration and reverse osmosis spiral wound membrane modules. All spacers had a similar geometry. Our studies showed that biofouling was not prevented by (i) variation of spacer thickness, (ii) feed spacer orientation, (iii) feed spacer coating with silver, copper or gold and (iv) using a biostatic feed spacer. At constant feed flow, a lower FCP and FCP increase were observed for a thicker feed spacer. At constant linear flow velocity, roughly the same FCP development and biomass accumulation were found irrespective of the feed spacer thickness: hydrodynamics and substrate load were more important for development and impact of biofouling than the thickness of currently applied spacers. Use of biostatic and metal coated spacers were not effective for biofouling control. The same small reduction of biofouling rate was observed with copper and silver coated spacers as well as uncoated 45° rotated spacers. The studied modified spacers were not effective for biofouling prevention and control. The impact of biofouling on FCP increase was reduced significantly by a lower linear flow velocity, while spacer orientation and spacer thickness in membrane modules had a smaller but still significant effect.

Screening of biofouling activity in marine bacterial isolate from ship hull

Biofouling is the undesirable accumulation of microorganisms, plants, algae and animals on submerged structures especially ship hulls. Biofouling also occurs on the surface of living marine organisms. It is also found on membrane systems such as membrane bioreactors and reverse osmosis spiral wound membranes. In the same manner, it is found in cooling water cycles of large industrial equipments and power stations. In the present study, totally 11 isolates were obtained from three ships from Royapuram harbour, Chennai, Tamil Nadu, India. Among the 11 isolates only DR4 showed maximum biofouling activity in the microtiter plate assay with a significant optical density of 0.596. Also an attempt was made to characterize the different biofouling bacterial isolates analyzing their morphological, biochemical and molecular characteristics. The results of the present study based on the above characteristics revealed that the isolate DR4 was similar to Bacillus sp. This study also highlights the need for a safe and natural antifouling agent to control the biofouling bacteria in the marine environment.

Modeling permeation of volatile organic molecules through reverse osmosis spiral-wound membranes

Reverse osmosis is an interesting process to eliminate organic solutes from distillery condensates before recycling them into the fermentation step. However, organic solutes transport phenomena through reverse osmosis membranes are specific. Rejection and sorption of five compounds were studied on a brackish water membrane. Acetic acid and 2,3-butanediol were not sorbed on the membrane while furfural and 2-phenylethanol presented strong sorption following the Langmuir pattern. These sorption effects coupled with solute molecular weight (MW) led to low rejections of acetic acid and furfural (30–60%) and high rejections of 2,3-butanediol and 2-phenylethanol (80–98%). With intermediate sorption and MW, butyric acid showed rejections between 70 and 80%. A modified solution-diffusion model was developed to take into account the sorption pattern and predict the concentration profile along the membrane on the retentate and permeate sides. Equilibrium properties were determined experimentally while transport properties were identified with data obtained from a synthetic condensate. This model was validated for various operating conditions with the synthetic and the industrial condensates. It was then used to simulate the influence of the recovery rate on the retentate and permeate concentrations. It showed the behavior differences between solutes with a linear sorption and solutes with a saturating sorption.

Treatment of dairy process waters by membrane operations for water reuse and milk constituents concentration

In the dairy industry non-accidental losses of milk or dairy products to sewer amount to 1–3% of the total milk processed. These significantly contribute to the 0.5–6.0 g COD/L of end-of-pipe wastewater. The major part of this polluting charge originates from starting, interrupting, and stopping dairy plant procedures, where milk-products are diluted with water and discharged to a purification station or collected to be spread on land. The very few works, that have been dedicated to the treatment of the so-called process waters (flushing waters, first rinse waters or “white waters”), show that nanofiltration (NF) or reverse osmosis (RO) is adequate for the concentration of milk components. The present work reports NF and RO performances (permeate flux, milk components rejection) of an effluent model solution (diluted skimmed milk). Performances of eight NF and RO membranes were compared by dead-end filtration. Crossflow experiments with NF and RO spiral-wound membranes confirm the results obtained by dead-end filtration. The results showed that one single membrane operation allowed the milk constituents to be concentrated in the retentate but reusable water of composition complying with the standard of purified water from process water was not reached. A finishing step (RO membrane, other) is needed for the production of reusable water.