Seawater Membrane Research Articles

On the discrepancy between nominal and effective charge density of polyamide reverse osmosis membranes

Quantitative and reliable information on the ionization of functional groups in polyamide (PA) active layers of thin film composite membranes is of vital importance for understanding and modeling of ion transport. Independent measurements using Ag+ ion-probing with RBS, XPS, or ICP-MS, indicate a nominal charge density in the order of 0.5 M. Conversely, model fitting to salt rejection experiments suggests an effective membrane charge at least three orders of magnitude lower for brackish water (BWRO) and seawater (SWRO) membranes. In this study we show that the original interpretation of the ion-probe experiments is inconsistent with the principles of ion partitioning used in ion transport models. We provide an alternative interpretation of ion-probe experiments in the literature, explaining the results through binding of silver ions to the carboxylic groups. By using this interpretation, the discrepancy between nominal and effective charge can be resolved: the Ag measured in the ion-probe experiments is mostly bound to the membrane (-COOAg, not –COO−/Ag+), while the membrane is virtually uncharged. Consequently, the ion-probe experiments can quantify the concentration of functional groups, but not theirpKa. We propose that confinement affecting membrane ionization, should be explicitly included in ion-transport modeling.

Evaluation of nanofiltration and reverse osmosis membranes for efficient rejection of organic micropollutants

Nanofiltration (NF) and reverse osmosis (RO) membranes have revolutionized water treatment processes. However, emerging separations, such as the removal of organic micropollutants (OMPs), pose a challenge for traditional RO and NF membranes due to either low water permeance (RO) or inadequate OMP rejection (NF). In this work, we investigated the rejection of thirteen frequently detected OMPs at environmentally relevant low feed concentration of 12 μg/L by using a wide range of commercial RO and NF polyamide thin-film composite (TFC) membranes and an in-house prepared NF membrane. The membranes were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), contact angle, and surface charge measurements. We investigated removal capabilities of OMPs at standard brackish water RO operating conditions (i.e., 15.5 bar transmembrane pressure, pH 8) and also examined the effect of feed solution transmembrane pressure on membrane performance. The rejection of ionic OMPs was strongly influenced by electrostatic repulsion effects, whereas rejection of non-ionic solutes was primarily driven by size exclusion and hydrophobic/hydrophilic interactions. The best performing TFC membranes — a lab-made semi-aromatic piperazine-based NF polyamide membrane and a fully aromatic commercial polyamide NF membrane (NF1) — displayed excellent rejection of OMPs comparable to a commercial RO seawater membrane (RO4), but exhibited ∼2-fold and ∼6-fold higher water permeance, respectively.

Selected physical and chemical cleanings remove biofilm in seawater membrane distillation without causing pore wetting

Membrane distillation (MD) is an emerging process with a proven ability to recover freshwater from streams with a wide range of salinities. However, MD is susceptible to biofouling. This study explores the efficiency of different cleaning strategies in biofilm removal during seawater MD. Hydraulic cleaning and chemical cleanings with 0.3%w w−1 ethylenediaminetetraacetic acid (EDTA), 0.3%w w−1 NaOCl, and 3%w w−1 citric acid were tested. The results showed that permeate flux recovery increased in the order of hydraulic cleaning <3%w w−1 citric acid <0.3%w w−1 NaOCl ≈0.3%w w−1 EDTA. Membrane cleanings substantially reduced the thickness of the residual biofilm layer and decreased its bacterial concentration and resistance to vapor pressure. The post-cleaning permeate conductivities were low suggesting that employed cleaning protocols did not cause pore wetting of hydrophobic polytetrafluoroethylene microporous (0.22 μm) membrane, and membrane rejection properties remained stable.

Modeling and optimization of salt and boron removal in reverse osmosis system

Seawater reverse osmosis (SWRO) is a mature technology that has significantly evolved over the past few decades. However, boron removal remains a serious challenge. A new RO transport model was developed by combining the irreversible thermodynamic theory and solution-diffusion theory and considering the solute concentration polarization phenomenon. The developed RO model supplemented by the use of variable solution properties and transport parameters was validated with existing data and, it was then applied to identify the main operation parameters and assess their effect on SWRO performance, with the aim of minimizing specific energy consumption and satisfying water quality requirements. The results showed that the solution-diffusion approach, cannot capture the interaction between transported boron and water species. For high pH, applied feed pressure, and flow rate, the convective transport of boron through the seawater membrane is remarkable and its contribution to the overall boron flux can reach over 20 %. The feed operating conditions have significantly influenced the quality of the water production and the amount of energy used. The results showed that the optimal SEC increased by approximately 40 %, and the recovery ratio decreased by 11.6 % as the feed flow rate increased from 0.002 to 0.005 m3/s.

Biofouling control of membrane distillation for seawater desalination: Effect of air-backwash and chemical cleaning on biofouling formation

This study explored the applicability of chemical cleaning and air-backwash to alleviate biofouling on seawater membrane distillation (SWMD). Membrane performance and wettability properties maintained at optimum duration and frequency of the treatments, as indicated by low permeate conductivity throughout the tests. The cleaning of the membrane using 2% NaOH by immersing the membrane for 30 min after 240 min operation removed the biofouling layer, indicated by low permeate conductivity of 370 µScm−1 after cleaning. However, more frequent membrane cleaning led to membrane damage, more severe wetting, and membrane hydrophobicity reduction. Ten-second air-backwash after 240 min of operation was also effective in controlling the biofouling, particularly when conducted at air pressure of 1 bar. More frequent air-backwash resulted in more aggravated inorganic fouling and accelerated biofouling formation due to the recurring introduction of air, leading to rapid membrane wetting.

Study for Recycling Water Treatment Membranes and Compnents towards a Circular Economy-Case of Macaronesia Area.

Desalination is an opportunity to get fresh water for irrigation and for drinking. Reverse Osmosis (RO) for sea water desalination is a solution for the high demand for water in Atlantic islands. The most efficient process to get desalinated water is RO; however, it is necessary to study what to do with the RO membranes used at the end of their life. This paper confirms the possibility to recycle them. The main categories of recycling by thermal processing commonly used in the industry include incineration and pyrolysis to produce energy, gas and fuel. These processes can be applied to mixed plastic waste, such as the combination of materials used in the manufacture of RO membranes. Recycling RO elements from desalination plants is shown to be an opportunity and pioneering initiatives are already underway in Europe. Energy recovery, via incineration, is feasible nowadays and it is a possibility to recycle RO membranes. On the other hand, the recycling of RO elements, via the pyrolytic industry, for fuel production could be centralized in a new industry already planned in the Macaronesia area and all obsolete osmosis membranes could be sent there for recycling. Recycling RO membranes is a very important opportunity for the environment and economy of the zone. This is a new business in water treatments with membranes, very interesting for decreasing the residues and the carbon footprint. The importance of this work is applied to sea water membranes, brackish water ones, and also wastewater tertiaries RO elements at the end of their life.

Elucidating biofouling over thermal and spatial gradients in seawater membrane distillation in hot climatic conditions

Biofouling is a hurdle of seawater desalination that increases water costs and energy consumption. In membrane distillation (MD), biofouling development is complicated due to the temperature effect that adversely affects microbial growth. Given the high relevance of MD to regions with abundant warm seawater, it is essential to explore the biofouling propensity of microbial communities with higher tolerance to elevated temperature conditions. This study presents a comprehensive analysis of the spatial and temporal biofilm distribution and associated membrane fouling during direct contact MD (DCMD) of the Red Sea water. We found that structure and composition of the biofilm layer played a significant role in the extent of permeate flux decline, and biofilms that built up at 45°C had lower bacterial concentration but higher extracellular polymeric substances (EPS) content as compared to biofilms that formed at 55 °C and 65°C. Pore wetting and bacterial passage to the permeate side were initially observed but slowed down as operating time increased. Intact cells in biofilms dominated over the damaged cells at any tested condition emphasizing the high adaptivity of the Red Sea microbial communities to elevated feed temperatures. A comparison of microbial abundance revealed a difference in bacterial distribution between the feed and biofilm samples. A shift in the biofilm microbial community and colonization of the membrane surface with thermophilic bacteria with the feed temperature increase was observed. The results of this study improve our understanding of biofouling propensity in MD that utilizes temperature-resilient feed waters.

Identification of cost and energy effective seawater membranes for use under hot climate conditions.

Seawater desalination using a cost-effective reverse osmosis system is crucial for hot climate countries suffering from water scarcity. The most favorable seawater membrane characteristics were identified under typical Egyptian operating conditions. Twelve different commercially available membrane elements were investigated. A reverse osmosis system was designed and simulated using available software (e.g., ROSA and IMSDesign). The characteristics of the most promising membranes were identified for operation at Matruh (Mediterranean Sea) and Sharm El-Sheikh (Red Sea). The present work shows that the lowest cost of seawater desalination is obtained with membranes having high salt rejection, high permeate flow, high membrane active area, and permeate flux greater than 0.914 m3 /(d·m2 ). Moreover, the cost of seawater desalination in summer is lower than in winter by 5% for Matruh and 2.7% for Sharm El-Sheikh. However, the impact of water salinity on the cost and specific energy consumption is higher than that of the seawater temperature. The cost of Mediterranean seawater desalination is lower than that of the Red Sea by 10.6%. Cost analysis at five different locations in Egypt shows that the highest cost takes place at Suez (Gulf of Suez), and the lowest cost occurs at Matruh (Mediterranean Sea). PRACTITIONER POINTS: Twelve different membranes were investigated for use under typical hot climate conditions. The cost of seawater reverse osmosis (RO) desalination is lower in summer by 2.7%-5% compared with winter. RO desalination costs up to 10.6% less for the Mediterranean Sea compared with the Red Sea. The optimum membrane element performance characteristics were identified for use under hot climate conditions.

Highly efficient size-sieving-based removal of arsenic(III) via defect-free interfacially-polymerized polyamide thin-film composite membranes

Serious health problems have been linked to the consumption and exposure of arsenic-contaminated groundwater. In comparison to As(V), As(III) is smaller and predominantly present in its neutral form in groundwater, which hinders its efficient removal by conventional nanofiltration and reverse osmosis membranes. In this study, the removal of As(III) was investigated at different pH conditions using three defect-free interfacially polymerized thin-film composite (TFC) membranes made by an optimized in-house developed interfacial polymerization process (KRO). The membranes were fabricated from aromatic para-phenylenediamine (PPD) or meta-phenylenediamine (MPD) and cycloaliphatic piperazine (PIP) by reaction with trimesoyl chloride (TMC). The PPD-KRO, MPD-KRO, and PIP-KRO polyamide membranes were tested with a feed containing 5 ± 1 mg L−1 (ppm) As(III). Two commercial TFC membranes, a seawater (Sepro RO4) and a nanofiltration (DOW NF270) membrane, were also evaluated for comparison. At natural conditions (pH 6–8), the defect-free fully aromatic TFC membranes demonstrated unprecedented size-sieving performance for As(III) removal with a rejection of ∼99.5 and > 99.8% for PPD-KRO and MPD-KRO, respectively, in comparison to ∼95% for the commercial Sepro RO4 seawater membrane tested under the same conditions. In contrast, As(III) rejection of semi-aromatic piperazine-based TFCs, PIP-KRO and NF270, showed a strong dependence on the charge-exclusion mechanism with maximum As(III) rejections of 69.5 and 46.3% at pH 10, respectively. Most notably, we demonstrated that the MPD-KRO membrane achieved an As(III) concentration ∼5 μg L−1 in the permeate (less than the WHO permissible arsenic standard level of 10 μg L−1), whereas PPD-KRO achieved a slightly higher value of ∼14 μg L−1. Our results are very promising considering the arsenic standard level in highly As(III) contaminated groundwater in Bangladesh and India is set at 50 μg L−1.

Group Contribution Method to Predict the Mass Transfer Coefficients of Organics through Various RO Membranes.

Reverse osmosis (RO) is a membrane technology that separates dissolved species from water. RO has been applied for the removal of chemical contaminants from water for potable reuse applications. The presence of a wide variety of influent chemical contaminants and the insufficient rejection of low-molecular-weight neutral organics by RO calls for the need to develop a model that predicts the rejection of various organics. In this study, we develop a group contribution method (GCM) to predict the mass transfer coefficients by fragmenting the structure of low-molecular-weight neutral organics into small parts that interact with the RO membrane. Overall, 54 organics including 26 halogenated and oxygenated alkanes, 8 alkenes, and 20 alkyl and halobenzenes were used to determine 39 parameters to calibrate for 6 different RO membranes, including 4 brackish water and 2 seawater membranes. Through six membranes, approximately 80% of calculated rejection was within an error goal (i.e., ±5%) from the experimental observation. To extend the GCM for a reference RO membrane, ESPA2-LD, 14 additional organics were included from the literature to calibrate nitrogen-containing functional groups of nitrosamine, nitriles, and amide compounds. Overall, 49 organics (72% of 68 compounds) from calibration and 7 compounds (87.5% of 8 compounds) from prediction were within the error goal.

Retardation of wetting for membrane distillation by adjusting major components of seawater

Wetting by fouling is phenomenon specific to membrane distillation (MD) and are regarded as challenges to the seawater membrane distillation (SWMD) process. To understand fouling and wetting, the influence of Mg and Sr crystals, which can potentially cause scaling, as well as Ca crystals deposited on the membrane surface were investigated. Mg(OH)2 and CaSO4 had significant impact on fouling and wetting. Even if CaCO3 and SrSO4 had no effects on fouling and wetting as single salts, CaCO3 and CaSO4 were dominant in synthetic seawater without Mg(OH)2. However, the occurrence of Mg(OH)2 scales became a cause for concern if Ca ion was removed from seawater for the prevention of fouling and wetting. Therefore, Mg as well as Ca should be removed for proper fouling and wetting control. NaOH/Na2CO3 softening was used for the removal of Ca and Mg ions. In addition, based on the inhibition effects of Mg ions on Ca scales, a new pretreatment method involving the injection of MgCl2 to increase the Mg /Ca ratio was examined.

Recycling of end-of-life reverse osmosis membranes for membrane biofilms reactors (MBfRs). Effect of chlorination on the membrane surface and gas permeability.

Reducing human impacts on drinking water is one of the main challenges for the water treatment industry. This work provides new results to support the recycling of EoL desalination reverse osmosis (RO) membranes for Membranes Biofilm Reactors (MBfRs). We investigate if the controlled-removal of fouling and polyamide layer may favor the use of these membranes in MBfRs. It also would allow establishing a normalized methodology of membrane recycling, regardless of inherited fouling during its lifespan. For this purpose, we transform by chlorination discarded brackish (BWd) and seawater (SWd) membranes into nanofiltration (BWt-NF and SWt-NF) and ultrafiltration (BWt-UF and SWt-UF) membranes. Our results show that chlorine attacks allow the fouling cleaning while improves the hydrophilicity and maintains roughness only in BWt-NF. Therefore, the bacterial deposition in this membrane is greater than the other tested membranes. Besides, the microcystin (MC) degradation capacity of BWt-NF verifies the compatibility of the chemical modification for the biological activity of MC-degrading bacteria. Finally, our results also provide that polyamide thin-film composite (PA-TFC) membranes, originally manufactured for salt rejection during desalination processes, offer competitive gases diffusion at low pressures. Therefore, we conclude that the membrane recycling may provide alternative low cost and gas permeable membranes for MBfRs, according to circular economy principles.

Effect of sodium hypochlorite exposure on polysulfone recycled UF membranes and their surface characterization

The present work aims to investigate the effect of chlorine on the surface of the polysulfone (PSF) layer uncovered in the transformed ultrafiltration (UF) membranes (recycled from end-of-life reverse osmosis (RO) membranes). With this purpose, 6 end-of-life RO membranes used previously during their useful life to treat brackish water or seawater were transformed using two higher exposure doses of free chlorine (50,000 and 300,000 ppm h). On one hand, the end-of-life membranes were first characterized in terms of the type of fouling identified by TGA, ICP and bacteria detection. On the other hand, to determine the stability of the PSF layer, the transformed PSF UF membranes were then characterized by means of its permeability and molecular weight cut-off (MWCO). In addition, membrane surface characterization was performed by ATR-FTIR, SEM and AFM. The results show that all the end-of-life RO membranes with organic and inorganic fouling were effectively transformed to PSF UF membranes at the ppm∙h values studied. However, one of the analysed sea water membrane model (HSWC3) showed more resistance to be transformed and the pores of the uncovered PSF layer only appeared at 300,000 ppm h. This membrane showed different surface appearance, with bigger pores after 300,000 ppm h exposure dose that might have affected the PSF UF membrane performance. This study indicates that a complete characterization of transformed PSF UF membrane surface is crucial for a deep understanding of the recycling process of end-of-life membranes.

Validation of recycled membranes for treating brackish water at pilot scale

Over the 65% of the installed desalination capacity is related on reverse osmosis (RO) membrane technology. However, membranes have to be replaced when fouling effect is irreversible. In fact, it is estimated that >840,000 end-of-life RO membranes modules are discarded annually at worldwide scale, mostly in landfills.In this study, end-of-life RO membranes were recycled at pilot scale by using concentrated solutions of free chlorine. Chemical attack enables the removal of polyamide layer partially or totally, obtaining nanofiltration (NF) and ultrafiltration (UF) membranes, respectively. 5 diverse end-of-life models were tested. Recycled membrane performance (permeability and rejection coefficients) was identified by filtering natural brackish water (BW). Further, validation test were conducted in order to analyze the recycled membrane stability by filtering BW long-term at Cuevas del Almanzora Desalination plant. For this purpose, two real pressure vessels with the capacity of hosting 6 membranes each were adapted. Recycled membranes did not show performance decline after 4month of filtration. Promising results have been observed. Recycled seawater membranes with properties between RO and NF were validated as potentially fusible membranes. Recycled BW membranes, with high sulphate ion selectivity, were evaluated as a potential alternative of the current NF commercial membranes.

Treatment of produced water originated from oil and gas production wells: a pilot study and cost analysis.

Produced water originated from oil and gas production wells was treated by a pilot-scale system including pre-treatment (chemical precipitation), pre-filtration, and post-filtration units. Pre-filtration unit consisted of sand filter, granulated activated carbon (GAC) filter, and ultrafiltration (UF) membrane. Post-filtration unit included reverse osmosis (RO) membrane unit. In this study, two different RO membranes including sea water (SW) and brackish water (BW) membranes were comparatively evaluated in terms of treatment and filtration performance. Besides, a cost analysis was conducted for a real scale RO membrane unit by using the data obtained from the pilot plant study. Average fluxes of 12.7 and 9.4L/m2h were obtained by SW and BW membrane units, respectively. Higher COD and conductivity removal efficiencies were obtained by SW membrane in comparison to BW membrane. Total cost of 0.88€/m3 was estimated for a RO plant treating produced water with a flowrate capacity of 300m3/d.

Detailed analysis of reverse osmosis systems in hot climate conditions

Hot climate countries require large amounts of desalinated water. The Reverse osmosis (RO) technique is currently considered the most reliable technique for brackish water and seawater desalination. However, its power consumption is considerably higher than all other techniques. Therefore, the present study investigates the performance of reverse osmosis plants in hot climate conditions. A typical Reverse osmosis system was designed, constructed and investigated. The ROSA software was also used for the analysis of seven different membrane elements. The experimental data were utilized in order to validate the simulation results of the ROSA software. A variance-based sensitivity analysis was performed in order to define the most effective design and operating parameters. The present investigation shows that the tap and brackish water membrane elements are more sensitive to the feed water temperature rather than the feed water pressure and concentration. Meanwhile, seawater membrane elements are more affected by the feed concentration. The detailed investigation of the different membrane elements shows that wastewater reclamation using reverse osmosis technology could be a significant source of low-cost fresh water for hot climate countries.

Comparative design of plug and recirculation RO systems; thermoeconomic: Case study

The main objective of this article is to determine which arrangement between the plug and recirculation reverse osmosis (RRO) is the optimal reverse osmosis (RO) system for a specific test case. Another objective is to compare the optimal operating conditions of these two arrangements. The RO system is designed to supply a water mass flow rate of 4000 m3/day for a 20-years period from Caspian Sea's brackish water to the city of Miarkelar, Iran. A multi-objective genetic algorithm is used to determine the best design of both arrangements of RO systems. Hence, feed water pressure, recirculated water flow rate, sea water membrane types, feed water flow rate and the number of elements in each pressure vessel were optimized. The objective function were the recovery rate and the unit production cost. Considering the optimal state of each arrangement, an exergy analysis has been performed. An exergy efficiency of recirculating and plug systems of 82.6% and 92.4% were obtained respectively. The thermo-economic analysis demonstrates that RRO results in a 36% decline in investment cost, 2% increase in operation cost, 6% recovery rate increment, and 19.7% permeate salt content decrease compared to the plug RO arrangement.

Adhesion potential of bacteria retrieved from intake seawater and membrane biofilms on full-scale reverse osmosis desalination process

AbstractMicro-organisms were isolated from intake seawater and reverse osmosis (RO) membrane biofilms collected from a full-scale membrane-based desalination process. The results from a culture-dependent approach using 12 media were combined with the microbial community structure on fouled RO membranes as analyzed by a 16S rRNA clone library construction in our previous study. This was followed by selection of 11 target bacteria for further analysis, which were suspected to be responsible for biofilm formation on membrane surfaces. The adhesion of potential biofoulants differing in surface hydrophobicity and charge was examined. Cell wall hydrophobicity was measured as the contact angle of a lawn of bacteria, and by adhesion to hexadecane. The cell surface charge was investigated by measuring electrophoretic mobility. The data obtained from these methodologies were compared. According to the cell surface charge measurements, Pseudomonas aeruginosa, Acinetobacter venetianus, Cellvibrio mixtus subsp. Mixtus...

Poly(vinyl) alcohol coating of the support layer of reverse osmosis membranes to enhance performance in forward osmosis

Membrane hydrophilicity influences the transport of water through the membrane in osmotically driven separations such as forward osmosis. In this paper, we coated the polysulfone support layer of two types of commercially available reverse osmosis membranes (brackish water and seawater) with hydrophilic polyvinyl alcohol (PVA). The aim of this was to increase the support layer hydrophilicity and, correspondingly, the rate of water transport through the membrane. Previous work with polydopamine coatings of the polysulfone support of reverse osmosis membranes has yielded promising results. In this work, we explore more readily available materials. Specifically, we studied the effects of two different PVA crosslinking agents – maleic acid and glutaraldehyde – on the resultant membrane properties and osmotic performance. For seawater membranes we found that PVA crosslinked to a limited degree with maleic acid creates a significant improvement in water flux in RO and FO systems, as compared to membranes with PVA crosslinked by glutaraldehyde. However, brackish water membranes did not have comparably significant changes in membrane performance. We conclude that the smaller pores of the brackish water membrane become clogged, and this effect is magnified by the lack of fractional free volume available within PVA that is highly crosslinked with glutaraldehyde.

The use of coconut choir as a raw material for the fabrication of seawater membrane desalination

The most problem were faced is fresh water scarcity. Seawater membrane desalination is one of the possible method to solve it. The made of membrane for desalination from coconut choir was the cheapest and easier alternative method. This study were doing step by step and started from making silica by synthetic processed, fabrication seawater desalination, membrane evaluation, and characterization’s membrane. Synthetic silica processed is using acidity technique with HCl. The fabrication of membrane processed is started by mixing silica weight 15 gram with centrifuge speed 500, 600, 700 rpm. The evaluation of membrane were testing with dead-end reactor. Characterization membrane by FTIR and SEM analysis. Seawater is contained salinity 34200 mg/l and TDS 336.200 mg/l. Based on evaluation of seawater membrane desalination by salinity and TDS permeate analysis the optimal membrane characteristic with silica weight 15 gram 600 rpm. Salt rejection value were 46,20% - 66,67% dan TDS rejection 87,27% - 90,72%.