Fouling Of Reverse Osmosis Membranes Research Articles

Combined impacts of aluminum and silica ions on RO membrane fouling in full-scale ultrapure water production facilities

In this study, a fouled reverse osmosis (RO) membrane from a full-scale ultrapure water (UPW) facility was autopsied and investigated to propose the fouling mechanism and mitigation strategies. Although the influent was introduced to the coagulation and ultrafiltration as the pre-treatment processes, thick fouling layers were found over the entire RO surface. The foulant was mainly composed of aluminum silicates due to the elevated Al concentration (up to 100 μg/L) originated from the coagulation process utilizing polyaluminum chloride, and high recovery (up to than 90%) of RO process. Lab-scale fouling tests also confirmed that the elevated Al concentration in the RO influent contributed to significant flux decline due to a bridging effect with negatively charged organic matter and the formation of aluminum silicates. The application of polydiallyldimethylammonium chloride as an alternative coagulant successfully mitigated the organic and silicate fouling. Therefore, control of the residual aluminum ions originated from the coagulation process is critical to mitigate both organic and inorganic fouling on RO membrane surfaces during the production of UPW.

Prediction of reverse osmosis membrane fouling in water reuse by integrated adsorption and data-driven models

In contemporary society, the reverse osmosis (RO) process is important for water treatment and reuse industry. However, membrane fouling remains a challenging issue during operation. To date, RO system operation mainly relies on the operator's knowledge, and the maintenance is carried out based on schedule or pre-defined criteria due to our limited understanding of RO fouling in real applications. To better understand the process and enable system optimization, an integrated data-driven coupled with adsorption model has been proposed in this study. The data-driven model calibrates the mechanistic model and predicts future values, while the adsorption model provides predictions on transmembrane pressure (TMP). By integrating these two models, an accurate prediction with high robustness and an insight into the detailed fouling mechanisms in real plants were achieved. In addition to the model itself, multiple regression analysis (MRA) had also been applied to identify the dominant fouling mechanisms. This analysis confirms that it is highly possible that membrane fouling is developed from an intermediate pore blockage to cake filtration.

Fouling of reverse osmosis membrane in sugar mill condensate purification under sub- and super-boundary flux conditions

The sugar production process, inherently water-intensive, is characterized by pronounced condensate formation during the evaporation and boiling phases. Given the environmental and resource implications, there is a scholarly emphasis on the potable reuse of such condensate by reverse osmosis (RO) in sugar mills. However, membrane fouling presents a significant challenge to the consistent operation of the RO process. This research examines the influence of operating parameters, namely transmembrane pressure and crossflow velocity, on the performance and fouling tendencies of an RO membrane during the purification of sugar mill condensate. The boundary flux theory was employed to model the permeate flux throughout this process. A boundary flux (5.92 L h−1m−2) and its corresponding operating pressure (10 bar) were determined. Moreover, a comparative analysis of the fouling mechanisms and the composition of the foulant layer under both sub-boundary and super-boundary conditions was undertaken. Under sub-boundary conditions, the fouling mechanism was identified as cake-intermediate blocking, while the super-boundary condition exhibited intermediate blocking. Under both conditions, organic fouling emerged as the primary fouling type. The TOC of surface contaminants ranged from 1.07 to 1.86 g/m2. Within this, proteins (484.0 to 850.3 mg m−2) and polysaccharides (201.5 to 379.2 mg m−2) were the dominant components. However, when operating conditions surpassed the boundary, there was a noticeable rise in inorganic fouling such as Ca (from 44.95 to 149.43 mg m−2) and Fe (from 4.40 to 112.09 mg m−2), which is likely due to the co-deposition of organic materials with inorganic ions. This research contributes to a more nuanced understanding of how operating conditions influence fouling mechanisms and provides foundational insights for addressing fouling challenges in sugar mill condensate purification.

Biofouling control of reverse osmosis membrane using free ammonia as a cleaning agent

Reverse osmosis (RO) is an important and widely-used membrane separation process for water recycling. However, biofouling is extensively considered a major problem for RO membranes due to the biofilm formation on the membrane surfaces. This study proposed and demonstrated a novel and sustainable chemical cleaning approach using a free ammonia (FA) solution for the removal of biofouling on RO membranes. The feasibility of FA solution for biofouling removal was investigated through a series of lab-scale soak cleaning tests and cross-flow cleaning tests on four fouled RO membranes (M1-M4) collected from municipal wastewater recycling plants. In soak cleaning tests on M1, FA concentrations of 65–560 mg NH3–N/L (pH = 8.9) can remove adenosine triphosphate (ATP) by 32–75 %, remove proteins by 18–47 % and remove polysaccharides by 31–74 %, which was up to 3.4 times of the removals by using NaOH solution under the same pH. FA solution of 310–560 mg NH3–N/L (pH = 8.9) even showed higher removals than NaOH solution with a higher pH of 11. In the cross-flow cleaning tests on M2-M4, FA solution of 310–560 mg NH3–N/L (pH = 8.9) removed the ATP by 82–100 %, removed proteins by 58–87 % and removed polysaccharides by 68–100 % in the fouling layers and increased the permeability by 8–16 %. Such cleaning effects in cross-flow tests were also positively correlated (R > 0.9, p < 0.05). Compared to the conventional anti-biofouling agent of NaOH solution (pH = 11), FA solution (310–560 mg NH3–N/L) showed significantly better cleaning performance. A high FA concentration of 560 NH3–N/L (pH = 8.9) could achieve comparable cleaning effect to 1 % EDTA solution (pH = 10). Additionally, increasing the frequency of cleaning or using a higher concentration of FA solution for biofouling removal will be more advantageous to prolong the membranes’ lifespan. The findings provide a promising alternative to using FA as a cost-effective and environmentally friendly solution for cleaning biofouling on RO membranes.

Identifying artifacts in EDS of fouled RO membranes through Raman and ICP-MS analysis

Fouled reverse osmosis (RO) membranes, primarily characterized by Scanning Electron Microscope and Energy Dispersive X-ray Spectrometer (SEM-EDS), face several limitations including spectral inaccuracies and misidentification of elements caused by automatic peak assessment software. This work addresses the latter by analyzing fouled polyamide membranes from community RO plants of Rajasthan treating brackish groundwater. Initially, EDS analysis revealed unexpected elements including Sc, Ti, V, and Cr, alongside anticipated foulants like Ca, Mg, Al, Si, Fe, and Mn. However, upon manual reassessment guided by spectral libraries and elemental likelihood, the peaks originally identified by the software as Sc, Ti, and V were reattributed to Ca and Ba, emphasizing the importance of careful peak assignment. Further, Raman spectroscopy of the same membranes detected calcite, dolomite, and molybdenum-bearing minerals. A peak initially assigned to Mo by the software was reinterpreted as interlayer carbonate, supported by literature on hydrotalcite structures. Subsequent ICP-MS analysis of the deposited salts showed that both Sc and Mo were below the detectable threshold, validating the reassessed findings. This study underscores the challenges of accurately identifying the inorganic scales to develop the right descaling approach by emphasizing the importance of integrating multiple analytical methods for comprehensive analysis and effective membrane cleaning solutions.

Fouling characteristics and flux prediction model of reverse osmosis membrane based on hydrophobic fractions in reclaimed water

During the operation of the reverse osmosis (RO) system, the identification of key fouling components and the prediction of flux changes based on these components are crucial for minimizing the costs associated with flux recovery. In this study, the DAX-8 resin fractionation method was employed to separate the organic matter in secondary effluent (SE) into hydrophobic acid substances, hydrophobic base substances, hydrophobic neutral substances (HON), hydrophilic substances, and hydrophobic substances (HOS). The primary objective was to discern critical membrane fouling components. The results revealed that HOS constituted 50.0%–60.0% of the dissolved organic carbon concentration in the SE, emerging as the pivotal fraction responsible for RO membrane fouling, contributing to 90.0% of the flux drop induced by SE. Additionally, a fouling prediction model employing two parameters quantified the fouling characteristics of distinct hydrophilic/hydrophobic fractions in RO treatment. Model fitting results indicated a flux decrease of 61.3%, 54.3%, and 46.7% caused by SE, HOS, and HON, respectively. Notably, 90.0% of the decrease in RO membrane flux induced by SE was attributed to the presence of HOS, with HON accounting for about 90.0% of this decrease. The results of the extended Derjaguin-Landau-Verwey-Overbeek theory demonstrated higher adhesion energy and cohesion energy between HOS and RO membrane surfaces compared to hydrophilic substances. This finding suggests that hydrophobic pollutants are more closely bound to RO membrane surfaces. Subsequently, an RO membrane flux prediction method based on HOS in reclaimed water was established. Predicting the RO membrane fouling characteristics of SE became feasible by measuring the concentration of HOS in the influent. Furthermore, resin pre-treatment mitigated the membrane fouling by removing HOS, and the HOS concentration was proposed as a new influent quality index for RO system design.

Adsorptive chito-beads for control of membrane fouling

Chitosan has excellent antimicrobial, adsorption, heavy metal removal, and adhesion properties, making it a good substitute for microplastic-based cleaners. Here, chitosan microbeads (chito-beads) of various sizes ranging from 32 μm to 283 μm were prepared via emulsion using a liquid on oil method and the feasibility of using them as an essential constituent in a chemical cleaning solution for a reverse-osmosis (RO) membrane-fouling-control process was assessed. Prior to the assessment the cleaning efficiency of a solution containing chito-beads, the interaction energy between chitosan and a representative organic foulant (humic acid (HA)) in a RO membrane fouling was analyzed using colloidal atomic force microscopy, and the strongest attraction between chitosan and HA was observed in an aqueous solution. When comparing the membrane cleaning efficiency of cleaning solutions with and without chito-beads, smaller chito-beads (32 μm and 70 μm) were found to have higher cleaning efficiency. Applications of chito-beads to the membrane cleaning process can enhance the cleaning efficiency through the physicochemical interaction with organic foulants. This study can widen the use of chito-beads as an additive to membrane chemical cleaning solutions to control membrane fouling in other membrane processes as well.

A comprehensive evaluation of the temporal and spatial fouling characteristics of RO membranes in a full-scale seawater desalination plant

The fouling of seawater reverse osmosis (SWRO) membranes remains a persistent challenge in desalination. Previous research has focused mainly on fouling separately; however, organic, inorganic, and biofouling can coexist and influence each other. Hence, in-depth study of the spatiotemporal changes in actual combined fouling in full-scale seawater desalination will provide more effective information for fouling investigation and control. In this study, we monitored (i) the operational performance of a full-scale desalination plant for 7 years and (ii) the development and characterization of membrane and spacer fouling at different locations of spiral-wound membrane modules sampled after 2.5-, 3.5-, and 7-year operation. The findings showed that (i) operational performance indicators declined with time (normalized flux 40 % reduction, salt rejection 2 % in 7 years), with a limited effect of the 20-day cleaning frequency, (ii) fouling accumulation in the membrane module mainly occurred at the feed side of the lead module and the microbial community in these area exhibited the highest diversity, (iii) the dominant microbial OTUs belonged mainly to Proteobacteria (43–70 %), followed by Bacteroidetes (10–11 %), (iv) Phylogenetic molecular ecological networks and Spearman correlation analysis revealed that Chloroflexi (Anaerolineae) and Planctomycetes were keystone species in maintaining the community structure and biofilm maturation and significantly impacted the foulant content on the SWRO membrane, even with low abundance, and that (v) fouling accumulation was composed of polysaccharides, soluble microbial products, marine humic acid-like substances, and inorganic Ca/Fe/Mg/Si dominate the fouling layer of both the membrane and spacer. Overall, variation partitioning analysis quantitatively describes the increasing contribution of biofouling over time. Ultimately, the organic‒inorganic-biofouling interaction (70 %) significantly contributed to the overall fouling of the membrane after 7 years of operation. These results can be used to develop more targeted fouling control strategies to optimize SWRO desalination plant design and operation.

Synergistic effect of ozone and non-oxidizing bacteriostatic agent on biofouling control of reverse osmosis membranes

Biofouling was the critical flaw of the reverse osmosis (RO) process. Both strong oxidizing and non-oxidizing bacteriostatic agents had obvious defects facing this problem. This study firstly compared the single and synergistic effect of a strong oxidizing agent (ozone) and a commercial non-oxidizing bacteriostatic agent (FR110) on RO membrane fouling control of reclaimed water, to find a more high-efficiency and practical approach. Consequently, the synergistic application of ozone and FR110 at low dosages effectively reduced the fouling of the RO membranes (18% normalized flux alleviation than the control group). Further analysis suggested that FR110 could induce a thinner fouling layer, while ozone pretreatment could lead to a loose fouling layer. The bacterial community analyses suggested that the relative abundance of biofouling-related genera was the key reason causing fouling differences. Phenotypic prediction confirmed the advantages of the synergetic application of FR110 and O3 in reducing the biofilm-forming capacity. Pure-strain experiments showed the synergetic application of FR110 and O3 could inhibit the overgrowth and secretion of certain biofilm-forming strains, such as Pseudomonas aeruginosa PAO1. In summary, synergistic disinfection was a promising way to regulate the bacterial community structure and biofilm-forming potentials, hoping for high-efficiency biofouling control in the RO system.

Detailed organic characterization of process water to evaluate reverse osmosis membrane fouling in industrial wastewater treatment

One of the major waste streams within the oil and gas (O&G) industry is produced and process water generated during hydrocarbon production and treatment, respectively. In gas production facilities, process water typically has lower salinity (i.e., <10,000 mg/L) which present opportunities for these wastewaters to be treated for beneficial reuse applications via advanced water treatment technologies, such as reverse osmosis (RO) membranes. One of the key challenges for RO membranes application to industrial wastewater treatment is fouling which is frequently attributed to the soluble organics present in the water and/or associated with field chemicals. In this study, a detailed organic characterization methodology, using liquid chromatography with organic carbon detector (LC-OCD) was applied to characterize the organics on a real process water collected from industrial wastewater treatment plant at a gas production facility. Additionally, a rigorous bench-scale testing procedure was implemented to assess the performance of a full-scale RO system with and without activated carbon filter (ACF) pretreatment, making this study the first one to apply LC-OCD methodology on real wastewater to evaluate the fouling of RO membranes deployed at an industrial treatment plant. Bench-scale RO results showed that in the absence of ACF pretreatment, a 12 % decline in membrane permeability (from 1.78 to 1.57 L/(m2-bar-h)) was observed, while no permeability decline was measured after ACF treatment. The organic fouling was confirmed by mass balance calculations on the bench scale experiments as well as Fourier Transform Infrared (FTIR) analysis on the membrane coupons. Moreover, LC-OCD analysis showed that the ACF inlet has a TOC concentration of approximately 3.06 mg/L; of those 1.29 mg/L (42 %) are hydrophobic, and 1.77 mg/L (58 %) are hydrophilic. After ACF treatment, the hydrophobic organics decreased to 0.65 mg/L, revealing that the ACF is removing >50 % of hydrophobic organics which are likely responsible for membrane fouling. Bench-scale operational and water quality results were comparable to the full-scale RO performance data validating the lab testing procedure implemented in this study.

Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles

The dissolution of silica and transparent exopolymer particles (TEP) can deposit on the membrane surface and cause serious membrane fouling in reverse osmosis (RO) technology. Coagulation, as a common pretreatment process for RO, can effectively intercept pollutants and alleviate membrane fouling. In this study, FeCl3 and AlCl3 coagulants and polyacrylamide (PAM) flocculants were used to explore the optimal coagulation conditions to reduce the concentration of silica and TEP in the RO process. The results showed that the two coagulants had the best removal effect on pollutants when the pH was 7 and the dosage was 50 mg/L. Considering the proportion of reversible fouling after coagulation, the removal rate of pollutants, and the residual amount of coagulation metal ions, the best PAM dosage was 5 mg/L for FeCl3 and 1 mg/L for AlCl3. After coagulation pretreatment, the Zeta potential decreased, and the particle size distribution increased, making pollutants tend to aggregate, thus effectively removing foulants. The removal mechanisms of pollutants by coagulation pretreatment were determined to be adsorption, electric neutralization and co-precipitation. This study determined the best removal conditions of silica and TEP by coagulation and explored the removal mechanism.

Mechanism of organic fouling in the reverse osmosis process of coal chemical wastewater

With the development and utilization of coal on a large scale, the treatment of coal chemical wastewater (CCW) had received extensive attention. This study utilized CCW from a coal liquefaction wastewater treatment plant to investigate the mechanism of organic fouling in the reverse osmosis (RO) process. CCW, which possessed high levels of organic matter, underwent RO process and resulted in significantly improved water quality, with a decrease in total organic carbon from 173.70 mg/L to 2.36 mg/L. However, the membrane surface was fouled by organic matter after continuous filtration for 14 h, causing a substantial reduction in the membrane flux, which decreased to 69.0 % normalized membrane flux. High molecular weight humic acid, the primary organic matter present in CCW, was found to be responsible for the organic fouling on the membrane surface, consistent with the main organic component of CCW. Moreover, organic foulants, including nitrogen heterocyclic compounds, alcohols, and lipids, were detected on the membrane surface. The study presented herein provides a comprehensive understanding and analysis of organic fouling in a RO system, offering crucial data support for the development of effective strategies to prevent and control RO membrane fouling in water treatment processes.

Differences in the Effect of Mn2+ on the Reverse Osmosis Membrane Fouling Caused by Different Types of Organic Matter: Experimental and Density Functional Theory Evidence.

Landfill leachate from some sites contains a high concentration of Mn2+, which may cause reverse osmosis (RO) membrane fouling during RO treatment. In this study, the effect of Mn2+ on RO membrane fouling caused by typical organic pollutants (humic acid (HA), protein (BSA), and sodium alginate (SA)) was systematically investigated, and it was found that Mn2+ exacerbates RO membrane fouling caused by HA, SA, and HBS (mixture of HA + BSA + SA). When the Mn2+ concentration was 0.5 mM and 0.05 mM separately, the membrane fouling caused by HA and SA began to become significant. On the other hand, with for HBS fouling only, the water flux decreased significantly by about 21.7% and further decreased with an increasing Mn2+ concentration. However, Mn2+ has no direct effect on BSA. The effect degrees to which Mn2+ affected RO membrane fouling can be expressed as follows: HBS > SA > HA > BSA. The density functional theory (DFT) calculations also gave the same results. In modeling the reaction of the complexation of Mn2+ with the carboxyl group in these four types of organic matter, BSA has the highest energy (-55.7 kJ/mol), which predicts that BSA binding to Mn2+ is the most unstable compared to other organic matter. The BSA carboxylate group also has the largest bond length (2.538-2.574 Å) with Mn2+ and the weakest interaction force, which provides a theoretical basis for controlling RO membrane fouling exacerbated by Mn2+.

Efficacies and mechanisms of different cleaning strategies for NF and RO membranes in a full-scale zero liquid discharge system

Membrane fouling conditions can be distinct for multi-step nanofiltration (NF) and reverse osmosis (RO) membrane processes in zero liquid discharge (ZLD) system. Customizing cleaning procedures according to fouling characteristics is imperative to improve the overall cleaning efficiency of the system. Herein, we performed four different “alkaline + acid” cleaning procedures, including alkaline solution (NaOH), acid solution (citric acid), metal chelating agents (Na2EDTA), and surfactants (SDS), on five fouled NF and RO membranes from a full-scale ZLD system for cold-rolling wastewater brine treatment. The“alkaline + acid” cleaning procedures were effective for organic and inorganic combined fouling removal in two-stage NF process, but failed to remove SiAl complex scaling completely for the 2nd RO process. Due to the slight membrane fouling, both performance and surface properties of 1st and 3rd pass RO membranes did not change significantly after the cleaning. The high pH-induced solubilization were the major mechanism for the removal of the SiAl complex. Na2EDTA/SDS addition caused the decrease of foulant-foulant and foulant-membrane interactions. Customizing membrane cleaning procedures based on membrane fouling characteristics can facilitate the stable operation of hybrid membrane system for the practical industrial wastewater ZLD treatment.

Water Use and Water Saving Strategies in Dialysis, Room for Improvement?

Dialysis treatment consumes a significant amount of water and energy, which entails an important waste management effort. Those variables play a relevant role on the total cost of a dialysis session. Strict dialysis water and ultrapure dialysis fluids standards were established as a pre-requisite for online convective therapies (e.g., hemodiafiltration), improving biocompatibility of the dialysis system, reducing inflammation profile of the dialysis patients, enhancing the responsiveness to erythropoiesis-stimulating agents and thus having the potential for improved survival. The main purification step of a dialysis water treatment system is the reverse osmosis. Fouling of reverse osmosis membranes remains a major issue and all effort should be made to reduce it, to ensure a constant output. Naturally occurring waterborne filamentous fungi, yeasts, bacteria and fragments may contaminate dialysis water and, consequently, dialysis fluids. To maintain the dialysis water treatment system under proper conditions and fulfilling the dialysis fluids quality standards there is a need of a significant effort, namely in terms of cleaning and disinfection procedures of the reverse osmosis, distribution systems and dialysis machines. Improving the reverse osmosis inlet water quality profile by installing an Ultrafiltration system as a pre-treatment, could have an impact in terms of dialysis water quality outcomes, water and energy consumption, and disinfection frequency. The water treatment system efficiency is strongly influenced by the system design and reverse osmosis setup. System design (i.e., not over dimensioned) with a clear focus on increasing efficiency is mandatory if one wants to decrease the carbon footprint. Dialysis prescription (namely dialysis fluid flow rates) plays an important role in the dialysis fluid consumption and consequently the water consumption. A more environmentally friendly dialysis can be influenced by optimization of the current technology and development of innovative technology, and by the adoption of a conscious and coherent behavior of all persons involved in the daily routine of a dialysis unit.

Fouling of Reverse Osmosis Membrane with Effluent Organic Matter: Componential Role of Hydrophobicity

Fouling of Reverse Osmosis Membrane with Effluent Organic Matter: Componential Role of Hydrophobicity

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.

Osmotic cleaning of typical inorganic and organic foulants on reverse osmosis membrane for textile printing and dyeing wastewater treatment

Reverse osmosis (RO) is one of the most fundamental membrane technology because it has higher salt rejections, which suffers from the issue of membrane fouling, as the membrane is inevitably exposed to foulants during the filtration process. For different fouling mechanisms of RO membrane, physical and chemical cleaning are widely used in the control of RO membrane fouling. The present study investigated the performance and water flux recovery using osmotic cleaning to clean the typical inorganic and organic foulants on RO membrane for textile printing and dyeing wastewater treatment. The effects of operation conditions (i.e., the concentration of cleaning solution, the filtrating time and cleaning time, and the flow rate of cleaning solution) on relative water flux recovery were examined. The results show that a highly water flux recovery (98.3% for cleaning of inorganic fouling and 99.6% for cleaning of organic fouling) was achieved under optimal operation of the concentration and flow rate of cleaning solution and the filtrating and cleaning time. Moreover, the experiment of repeated “filtrating-cleaning” cycles indicated that the osmotic cleaning has highly performance of recoverability of water flux (over 95.0%) can be extended in a relatively long time. The experimental results and changes on SEM and AFM images of RO membrane confirmed the successful development and application of osmotic cleaning for inorganic and organic fouling of RO membrane.

Supercritical carbon dioxide fluid cleaning of extracellular polymeric substance surrogates on seawater reverse osmosis membranes

Fouling of seawater reverse osmosis (SWRO) membranes cause of reduced water flux and increased energy usage, which requires frequent cleaning to maintain performance. We demonstrate Supercritical carbon dioxide (sCO2) fluid, as an alternative membrane cleaning reagent, can effectively remove extracellular polymeric substances (EPS) that form on SWRO membranes. Carbon dioxide (CO2) gas was turned into sCO2 fluid by elevating the pressure (to 7.5 MPa) and temperature (to 35 °C). The SWRO membrane coupons were fouled by EPS surrogate materials (sodium alginate or bovine serum albumin), and the sCO2 cleaning was conducted to recover the deteriorated water permeation flux. We present that the sCO2 cleaning can effectively eliminate the EPS surrogate materials from the membrane surface with a great cleaning efficiency (75–90 %). In addition, it was observed that sCO2 cleaning does not alter the properties (i.e., surface functional groups and salt-rejecting performance) of polyamide-based SWRO. Our findings suggest that sCO2 is applicable to remove EPS surrogate materials from the membrane.

Performance of resin adsorption and ozonation pretreatment in mitigating organic fouling of reverse osmosis membrane

Effective pretreatment of reverse osmosis (RO) influent is of great importance for reducing membrane fouling risks during coking wastewater desalination. In this study, the combined resin adsorption and ozonation pretreatment was investigated on alleviating RO membrane organic fouling. The performance of combined process was compared with only resin adsorption or ozonation, which was evaluated in terms of changes in chemical oxygen demand (COD), ultraviolet-visible index, and three-dimensional excitation-emission matrix fluorescence spectra. RO membrane fouling tests were conducted to examine the effects of pretreatment on flux decline and filtration resistance. The surface morphology and functional groups of membrane before and after fouling was characterized by scanning electron microscopy and infrared spectroscopy. The correlation between major organic matter in the wastewater and normalized RO membrane flux was established via multiple linear regression equations. The results showed that ozonation was more effective in removing COD and fluorescent organics than resin adsorption. Moreover, the combined bifunctional resin adsorption/ozonation unit showed the best performance, with COD and UV254 removal rates of 49.4 % and 88.0 %, respectively. The fluorescence intensity of each component decreased significantly. Meanwhile, the polysaccharide and protein components of the RO membrane fouling layer were effectively reduced by 67.2 % and 80.8 %, respectively. Most importantly, the combined pretreatment substantially reduced the decline in membrane flux and filtration resistance. Meanwhile, the fulvic acid-like organics in the wastewater showed high correlations with normalized membrane flux. The regression equation was beneficial for RO membrane fouling evaluation.