Spiral Wound Reverse Osmosis Membrane Research Articles

Reverse osmosis desalination combining feed flow reversal with permeate flush for mitigation of mineral scaling

The performance of a spiral-wound reverse osmosis (RO) membrane system, operating in a cyclic mode of normal feed flow (NFF)-feed flow reversal (FFR), was evaluated for desalting feed water of high gypsum mineral scaling potential. The membrane system, with six membrane elements in series, was operated without antiscalant dosing at the condition of gypsum supersaturation at the membrane surface of the tail RO element. Automated NFF/FFR switching was triggered by an optical membrane monitoring system (MMS) installed at the last membrane element. This element alternated from being the tail to lead element at NFF and FFR modes, respectively. Multicycle NFF/FFR operation demonstrated partial cycle-to-cycle restoration of the permeate flux. However, progressive flux decline was noticeable with increased NFF/FFR cycles. Complete restoration of element productivity (in terms of permeate flux) was attained via permeate flushing (at the early membrane scaling stage) owing to gypsum scale dissolution. The study results suggest that NFF/FFR RO operation under conditions of high mineral scaling potential can be effectively combined with periodic permeate flushing. However, establishing the long-term approach feasibility will require a strategy for optimizing the frequency of NFF/FFR switching and permeate flushing in relation to the feed water quality and desalting operating conditions.

A model for the observed secondary-maximum in backwash-effluent-TDS-data obtained during backwash of spiral-wound RO membranes

Observation of a “secondary maximum” in the effluent Total Dissolved Solids (TDS) concentration data, during back-washing of micro-scale spiral-wound Reverse Osmosis (RO) membranes, has been reported (Varma and Chatterjee, 2023). This observation is of interest because a “wash-out” process for any system, may be expected to produce effluent water, which shows an exponential decline in the contaminant, from its initial peak concentration, to that of the water used for washing. Hence the observation of a “secondary maximum” in the back-wash effluent TDS data is interesting and has been examined experimentally in (Varma and Chatterjee, 2023). In this work, we present a mathematical model, which can explain the above observations. This model shows that high TDS water is trapped in the RO membrane element, when the RO system is shut-off. A complete wash-out of this high TDS water, which is held close to the membrane surface requires RO permeate osmotic backwash of a “critical” volume. This “critical” RO permeate volume, can be estimated from the method used in this study. The model is based on coupled-unsteady-state material balances for the salt held in different pseudo-compartments within the RO membrane module.

Fouling of reverse osmosis membrane: Autopsy results from a wastewater treatment facility at central park, Sydney

Membrane fouling is an inevitable phenomenon and common issue in Reverse Osmosis (RO) membrane systems used for water reclamation. Severe membrane fouling in RO system could consequently increases the operation cost as it requires frequent membrane chemical cleaning process thus consuming more chemical agents and shorten lifespan of RO membrane module. In this study, potential foulants of RO membranes that are used at Sydney's urban wastewater recycling facility which treated for domestic and commercial wastewaters, were investigated via membrane autopsy method. The three-year-old spiral wound RO membrane modules were taken from the site for membrane autopsy and to investigate major fouling factors as well as in-depth study of fouling mechanisms throughout various characterization methods. Additionally, a flux recovery rate of fouled RO membranes via the chemical cleaning was also examined using different kind of chemical cleaning agents to find a most effective chemical cleaning combination.

Hierarchical isoporous membrane filters for simultaneous reduction of pressure drop and efficient removal of nanoscale airborne contaminants

Isoporous membranes with well-defined pore architectures offer a unique design approach to achieve a multi-scale porous network. For instance, isoporous membranes with progressively smaller pore sizes can be stacked to create a hierarchical pore network in which each length scale and the gradient of the pore network are deterministic by design. In this paper, we introduce a hierarchically-arranged multilayer isoporous air filter that comprises an ultrathin (thickness <1μm) nanoporous active filtration layer and a microporous support layer. To maximize airflow and thereby reduce pressure drop across the membrane, we engineered a gap between the nanoporous and microporous membranes by designing and fabricating microscale spacer structures akin to feed spacers used in spiral wound reverse osmosis membranes. We demonstrated that such hierarchical isoporous membranes with integrated spacers (HIM-S) can retain high filtration efficiency (>95%) for ultrafine, most penetrating particle size (MPPS) while simultaneously reducing the pressure drop across the membrane (by ∼86%).

Antimicrobial and Antibiofouling Electrically Conducting Laser‐Induced Graphene Spacers in Reverse Osmosis Membrane Modules

AbstractBiofouling is an ongoing challenge for water treatment membrane processes. Reducing biofilm growth on the membrane surface or on the polymeric feed spacer will reduce operation, maintenance, and module replacement costs. Laser‐induced graphene (LIG) is a low cost, environmentally friendly, electrically conductive carbon material shown to have antibiofouling properties. Here it has been shown that an electrically conductive LIG‐coated polypropylene (PP) feed spacer has both antimicrobial and antifouling effects under a low electrical current, and when implemented into a spiral wound membrane module reduced biofilm growth on both the membrane and the spacer components. The antibacterial property of the LIG spacer is tested using Pseudomonas aeruginosa and the brackish water Rheinheimera sp. as model organisms. Using a voltage of 12 V, P. aeruginosa is completely inactivated in 10 h, while a dynamic accumulation assay employing Rheinheimera sp. showed significant reduction (p &lt; 0.05) in bacterial adhesion compared to an uncoated spacer. The spacer is incorporated into a spiral wound reverse osmosis (RO) membrane module, and reduced biofouling is observed on both the membrane and LIG spacers components using brackish water and 12 V. This study demonstrates the feasibility of electrically conductive feed spacer components in spiral wound RO membrane modules.

Candida krusei is the major contaminant of ultrafiltration and reverse osmosis membranes used for cranberry juice production

Ultrafiltration (UF) and reverse osmosis (RO) are commonly used for the clarification and concentration of fruit juices. However, one of the main limitations of filtration membranes is biofouling, which reduces membrane efficiency and can contaminate the filtered product and lead to spoilage. In this study, the microbial fouling layers of UF and RO membranes from a Canadian cranberry juice processing plant were characterized. Unlike the microbiota found in cranberry juice, which is dominated by Bacillus sp. and other bacteria, both UF and RO membranes were mainly colonized by several strains of the yeast Candida krusei. A variation in bacterial and yeasts count was observed between tubular UF and spiral-wound RO membranes, and the analysis of the spatial distribution highlighted the homogeneity of the contamination across each membrane. Surprisingly, RO membranes had a higher level of contamination when compared to UF membranes. Furthermore, six strains of C. krusei were further characterized through multilocus sequence typing analysis, five of which exhibited unique allelic profiles and two of which were found to contain a new TRP1 allele.

Biofouling of reverse osmosis membranes: assessment by surface-enhanced Raman spectroscopy and microscopic imaging

The decline in the performance of spiral-wound reverse osmosis (SWRO) membranes is frequently due to biofouling. This study focus on qualitative and quantitative diagnosis of SWRO membrane biofouling. Bacterial counts on the different surfaces of the fouled membranes were carried out. Surface enhanced Raman spectroscopy (SERS) was performed to highlight clogging materials as well as their natures and identity. The topography of the fouled membranes and the structures of biofilms were visualized by fluorescence microscopy (FM) and scanning electron microscopy (SEM). The results indicated the presence of bacteria in the different SWRO membrane areas. Those strongly adhered were significantly higher than those weakly. It varied between 26 × 105 and 262 × 105 CFU m−2. However, SERS mapping showed different fouling levels and the thickness of the fouling layer was 5 µm. Microscopic imaging revealed biotic and abiotic deposits. These data can together allow better management of the seawater desalination process.

Performance of biofouling mitigating feed spacer by surface modification using quorum sensing inhibitor

Feed spacers are essential components in spiral-wound reverse osmosis (RO) membrane modules and form gaps between membranes while enhancing mass transfer during RO membrane operation. Despite these advantages, long-term operation of feed spacers has considerable influence on biofouling of the membrane filtration process. In this study, biofouling reduction effects were achieved by coating the surfaces of polypropylene (PP) feed spacers with vanillin, which is nontoxic to marine life and highly hydrophilic. A mussel-inspired material, polydopamine (PDA), was also applied for spacer modification to improve the binding forces of both vanillin and polyamide (PA) layer of the membrane. Two coating method was used: PDA was precoated on the surface of PP prior to the vanillin coat (PDA-V spacer) and vanillin co-deposited with polydopamine (PCV spacer). Experimental results showed that the PCV spacer was more appropriate for preventing biofilm formation than the PDA-V spacer, up to 96.7 % and 85.7 % decrease in umber of bacteria for PCV and PDA-V samples, respectively, by delaying microbial community formation. On the other hand, the coated layer eventually peels off when the samples are submerged under water for 100 days or more.

Brine minimization in desalination of the geothermal reinjection fluid by pressure-driven membrane separation processes

Brine obtained during water treatment by pressure driven membrane processes remains the major drawback. Therefore, it is of paramount important to find a lasting solution in order to minimize its production by both nanofiltration (NF) and reverse osmosis (RO) membranes. In this study, an experimental study with the aim of brine minimization during membrane desalination of the geothermal reinjection fluid using a mini-pilot scale membrane test system having spiral wound NF and RO membranes was conducted. The membranes employed for this task were TR-NF and BW30-RO membranes. First, studies with different brine to feed ratios of 1:4, 1:3, 1:2 and 2:3 represented as NF-F2, NF-F3, NF-F4 and NF-F5, respectively were investigated using TR-NF membrane. A control study with no brine recirculation was conducted as well in order to check the effect of brine recirculation on the membrane performance. Secondly, studies with BW30-RO membrane using same brine to feed ratios as in the case of NF membrane studies were carried out. An applied pressure of 15 bar, initial water recovery of 60% and 4 h of experimental time were employed as operational conditions for both NF and RO membrane studies. Based on the results obtained, it was found that the brine recirculation (with a brine to fresh feed ratio of 2:3) has a significant impact on the permeate flux. The product water can be utilized for the agricultural irrigation purposes. Nevertheless, the boron concentration in the product water was still high for the sensitive crops.

Performance enhancement of spiral-wound reverse osmosis membrane elements with novel diagonal-flow feed channels

Spiral-wound reverse osmosis membrane elements have been widely applied in household water purification which usually demand a high water recovery rate. Membrane scaling remains an intractable hurdle which would deteriorate the performance of membrane elements. In this study, we developed a novel feed channel with diagonal flow direction, for which the performances were examined by filtration experiments on real membrane elements and the impacts of channel configuration were analyzed via the coupling of computational fluid dynamics simulation with response surface methodology. The results showed that the membrane element with the novel diagonal-flow feed channels exhibited a higher water flux along with lower declining rate and higher salt rejection than the conventional one with axial flow direction. The alteration of water flow direction could considerably increase the average cross-flow velocity in the channel, thus enhancing mass transfer and reducing concentration polarization. For a targeted water recovery of 75% and water flux of ~45 L/(m2·h), the optimal configuration regarding the width ratios of the wide and the narrow openings at inlet/outlet of diagonal-flow feed channels are suggested within the range of 20–43% and 5–10%, respectively. The diagonal-flow feed channel has a promising application prospect for membrane scaling control.

Understanding the operational problems and fouling characterization of RO membrane used for brackish water treatment via membrane autopsy.

An autopsy of spiral wound reverse osmosis (RO) membrane operated in brackish water treatment was conducted to understand the origin and extent of foulants and fouling mechanisms. Structural and chemical characterization was determined by visual inspection and instrumental analysis such as scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). It was observed that the membrane surfaces were completely covered with a gray/brown pollutant layer in all membrane sheets. SEM images proved accumulation of mineral pollutants on membrane surface. Also, high levels of Al and Si, which were attributed to aluminum silicates originating from feed water, were determined on membrane surfaces. Additionally, the XRD analysis results showed that the foulant sample collected from membrane surfaces included halloysite, SiO2 and LiCl components. Fujiwara's result proved that no damage occurred on the membrane surface due to oxidation. Consequently, a fouling control strategy for RO-based brackish water treatment plants was also recommended to increase the membrane life.

Analysis of Concentration Polarisation in Full-Size Spiral Wound Reverse Osmosis Membranes Using Computational Fluid Dynamics.

A three-dimensional model for the simulation of concentration polarisation in a full-scale spiral wound reverse osmosis (RO) membrane element was developed. The model considered the coupled effect of complex spacer geometry, pressure drop and membrane filtration. The simulated results showed that, at a salt concentration of 10,000 mg/L and feed pressure of 10.91 bar, permeate flux decreased from 27.6 L/(m2 h) (LMH) at the module inlet to 24.1 LMH at the module outlet as a result of salt accumulation in the absence of a feed spacer. In contrast, the presence of the spacer increased pressure loss along the membranes, and its presence created vortices and enhanced fluid velocity at the boundary layer and led to a minor decrease in flux to 26.5 LMH at the outlet. This paper underpins the importance of the feed spacer’s role in mitigating concentration polarisation in full-scale spiral wound modules. The model can be used by both the industry and by academia for improved understanding and accurate presentation of mass transfer phenomena of full-scale RO modules by different commercial manufacturers that cannot be achieved by experimental characterization of the mass transfer coefficient or by CFD modelling of simplified 2D flow channels.

Aggravated biofouling caused by chlorine disinfection in a pilot-scale reverse osmosis treatment system of municipal wastewater

Abstract The reverse osmosis (RO) system is widely applied to produce reclaimed water for high-standard industrial use. Chlorine disinfection is the main biofouling control method in the RO systems for wastewater reclamation. However, researchers reported the adverse effects of chlorine disinfection which aggravated biofouling in laboratory-scale RO systems. In this study, four parallel 4-inch spiral wound RO membranes were used to study the effect of chlorine on biofouling in a pilot-scale RO system. The free chlorine dosages in four experimental groups were 0, 1, 2 and 5 mg/L, respectively. After continuous chlorination and dechlorination, the feed water entered the RO system. It was found that chlorine pretreatment caused a 1.9–36.7% increase in relative feed water pressure of the RO system, suggesting that chlorine aggravated the membrane fouling in the pilot-scale RO system. The microbial community structures of living bacteria in the feed water of the RO system were determined by the PMA (propidium monoazide)-PCR method and showed that the relative abundance of chlorine-resistant bacteria (CRB) was significantly increased after disinfection. Nine major genera which maintained higher relative abundance in experimental groups with high chlorine dosage were considered as possible key species causing membrane fouling, including Pedobacter, Clostridium and Bradyrhizobium.

Novel Magnetic Resonance Measurements of Fouling in Operating Spiral Wound Reverse Osmosis Membrane Modules

A novel magnetic resonance measurement (MRM) protocol for non-invasive monitoring of fouling in spiral wound reverse osmosis (SWRO) membrane modules is demonstrated. Sodium alginate was used to progressively foul a commercial SWRO membrane at industrially relevant operating conditions in a circulating flow loop. The MRM protocol showcased the following: (i) earlier, more sensitive detection and quantification of fouling in the membrane module compared to feed-channel pressure drop. This was achieved using appropriate detection of the total nuclear magnetic resonance (NMR) signal. (ii) 2D cross-sectional imaging of the location of the accumulated foulant material; this was preferentially located adjacent to the membrane spacer sheet nodes, which was subsequently confirmed by a module autopsy. This image contrast, which could also readily differentiate the membrane, feed spacer and permeate spacer regions, was realised based on differences in the NMR relaxation parameter, T2,eff. (iii) High frequency acquisition of 2D cross-sectional velocity images of the module revealing very localised flow channelling in response to gradual foulant accumulation which impacted significantly on the flow pattern within the central permeate tube. Collectively this NMR/MRI measurement protocol provides a powerful analysis tool for the evolution of fouling in such complex modules, thus ultimately enabling more informed module design.

Grey water treatment with spiral wound UF and RO membranes

A typical combination of spiral wound ultra-filtration and spiral wound reverse-osmosis membranes were used to treat grey water obtained from washing machine discharge in order to recover the surfactant solution as well as water both of which could be reused for another couple of washes. The process leads to the separation of dirt and dust particles from the grey water using the UF process and later the surfactant solution and water is separated from the mixture using the reverse osmosis membrane. Various backwash and backwash-backflush methods were used to increase the membrane performance by decreasing the fouling problems which generally occurs in such types of membranes. These backwashing procedures were found to have enhanced the life of the membrane by cleaning the membranes. The TDS and turbidity of the solution mixtures were analyzed by conductivity meter and turbidity meter respectively and the results obtained from these instruments provided a good idea regarding the separation processes. The UF membranes could decrease the turbidity of a dirty mixture solution but allows the surfactant solution to pass though it which is finally treated using the RO membranes which could decrease both the turbidity and TDS of the solution. The experiment provides a comprehensive idea related to the treatment of grey water which could help in better waste water reuse as well as economic ways of reusing detergents for subsequent washes.

Modeling of pressure drop in reverse osmosis feed channels using multilayer artificial neural networks

This paper presents a data-driven model of pressure drop in spiral wound reverse osmosis membrane channels with the aid of computational fluid dynamics (CFD) simulations and multilayer artificial neural networks (MLN) method. Typical industrial spacer structures are considered in the CFD models to ensure practicability. To generate adequate data for MLN training, three-dimensional (3D) CFD model problems with respect to 500 different design parameter combinations are solved with a high-performance computing (HPC) strategy. With the HPC strategy the efficiency of CFD simulations is improved by about 50 times. The proposed MLN method is then used to correlate the pressure drop considering 7 design parameters, which enables a quantitative description of geometric structures and operation conditions for improvement. The accuracy of the MLN prediction on the test set is 99.734%. The obtained results show that the performance of the predictive model is comparable to alternative approaches in previous literatures. The proposed method has potential applications in intricate PDE-constrained optimization problems involving CFD simulations due to its high computational efficiency.

Analyzing and verifying the association of spiral-wound reverse osmosis membrane fouling with different secondary effluents: full-scale experiments

In order to analyze and verify the association of the reverse osmosis (RO) membrane fouling with water quality in full-scale plants, two RO systems (40, 000 m3/d and 20, 000 m3/d) treating different secondary effluents were operated in parallel. The quality of secondary effluents and the performance of RO systems were monitored over 12 months. Difference in foulants distribution and fouling layer composition between the two systems were evaluated by membrane autopsy and foulants characterization. Results verified that: 1) the secondary effluent from municipal sewage caused more serious membrane fouling; 2) more foulants deposited on the surface of leading membrane both in two systems (3.11 ± 0.15 g/m2 and 2.93 ± 0.13 g/m2); 3) the microbial community on the RO membrane surface contained more colonizing bacteria in the system treating municipal sewage secondary effluent ; 4) organics in the secondary effluent facilitated biofouling while higher ion concentration restrained biofouling.

An analysis of the effects of pressure-assisted osmotic backwashing on the high recovery reverse osmosis system

Abstract The low cost simplified method for implementation of pressure-assisted osmotic (PAO) backwash (BW) for spiral wound reverse osmosis (RO) membrane module is presented in this work. The effect of membrane design and an operating parameter concerning the efficiency of PAO membrane BW is analyzed. The following design and operating parameters are considered in this study: (i) spacer thickness, (ii) dimension of the permeate channel, (iii) number of leaves, and (iv) BW water pressure. The performance of PAO BW with respect to membrane cleaning efficiency is analyzed for three different high recovery RO systems by purifying 1,500 liters of water. The membrane cleaning efficiency is measured by examining the rate of permeate quality and quantity decline using ASTM D4516 method. Finally, to quantify the membrane fouling with respect to different high recovery configurations, the thickness, and composition of foulants present in the used membrane's surface are measured by using field emission scanning electron microscope with energy dispersive X-ray (FESEM-EDX). The result concludes that the RO membrane operated at high recovery with PAO BW is found to have less fouling deposits than membrane without PAO BW.

Pilot-Scale Assessment of Urea as a Chemical Cleaning Agent for Biofouling Control in Spiral-Wound Reverse Osmosis Membrane Elements.

Routine chemical cleaning with the combined use of sodium hydroxide (NaOH) and hydrochloric acid (HCl) is carried out as a means of biofouling control in reverse osmosis (RO) membranes. The novelty of the research presented herein is in the application of urea, instead of NaOH, as a chemical cleaning agent to full-scale spiral-wound RO membrane elements. A comparative study was carried out at a pilot-scale facility at the Evides Industriewater DECO water treatment plant in the Netherlands. Three fouled 8-inch diameter membrane modules were harvested from the lead position of one of the full-scale RO units treating membrane bioreactor (MBR) permeate. One membrane module was not cleaned and was assessed as the control. The second membrane module was cleaned by the standard alkali/acid cleaning protocol. The third membrane module was cleaned with concentrated urea solution followed by acid rinse. The results showed that urea cleaning is as effective as the conventional chemical cleaning with regards to restoring the normalized feed channel pressure drop, and more effective in terms of (i) improving membrane permeability, and (ii) solubilizing organic foulants and the subsequent removal of the surface fouling layer. Higher biomass removal by urea cleaning was also indicated by the fact that the total organic carbon (TOC) content in the HCl rinse solution post-urea-cleaning was an order of magnitude greater than in the HCl rinse after standard cleaning. Further optimization of urea-based membrane cleaning protocols and urea recovery and/or waste treatment methods is proposed for full-scale applications.

Calculation of the Cross Section Active Area for a Polymeric Spiral Wound Reverse Osmosis Membrane

Cross flow filtration is the typical way that water is filtered in membrane technology; that means that feed solution passes tangencially over the membrane and rejected components are washed away of the membrane by the rejected stream. In such a way, that minimal solids building up and at constant low flow resistance are achieved. In this paper, a calulation method regarding to the value of cross-section active area for a polymeric spiral wound reverse osmosis (RO) membrane is presented, in order to obtain the value of the cross-flow velocity of the system. This velocity is needed to improve the knowledge fouling mechanisms and it is not easy to know without obtaining the cross section area. To determine cross-section area of a RO polymeric spiral wound membrane a series of calculations were performed to obtain the initial values of some parameters. The mathematical calculation was also achieved with the Roll Length program. Based on the results obtained, it was concluded that only 65.36% of the total cross-section of the membrane is useful to cross flow and it was possible to determine the active cross-section of filtration with a value of 1,915.4 mm2, for the membrane studied. This methodology allows the calculation for any RO spiral membrane.