Forward Osmosis Fouling Research Articles

A general modeling framework for FO spiral-wound membrane and its fouling impact on FO-RO desalination system

Modeling fouling in forward osmosis (FO) spiral-wound membrane (SWM) is challenging due to the time-dependent nature of fouling and the complex flow patterns induced by baffle. This necessitates the development of a general modeling framework for FO SWM module that prioritizes both accuracy and ease of implementation. This framework was validated against FO SWM experiment data from previous work, demonstrating a reasonable agreement with a maximum error of 13.1 % in FO permeate flux. This validated model was used to study the impact of fouling on feed recovery, a critical factor influencing specific energy consumption (SEC) in FO-RO desalination systems. While improved operating conditions and membrane parameters (A, Ss and Cf) initially lead to increased water flux, this effect was significantly counteracted by accelerated fouling. Consequently, performance improvements in terms of flux and SEC remained minimal (<1 %) under severe fouling conditions. The results show that for foulant cake with larger pore diameter (>10 nm), the contribution of mechanical resistance is insignificant compared to osmotic resistance. However, the contribution of mechanical resistance becomes important for foulant cakes with pore diameter smaller than 10 nm. This paper shows that modeling have evolved to a stage that they can be used to understand membrane fouling phenomena at the SWM module scale.

Fertilizer-driven FO and MD integrated process for shale gas produced water treatment: Draw solution evaluation and PAC enhancement

It is a great challenge for effective treatment of shale gas produced water (SGPW), a typical industrial wastewater with complex composition. Single forward osmosis (FO) or membrane distillation (MD) process has been widely used for desalination of SGPW, with membrane fouling not well addressed. Fertilizer draw solution (DS) with high osmotic pressure is less likely to cause FO fouling and can be used for irrigation. An integrated process using fertilizer-driven FO (FDFO) and MD process was proposed for the first time for SGPW treatment, and characteristics of fertilizer DS and powdered activated carbon (PAC) enhancement were assessed. The DS using KCl and (NH4)2SO4 had high MD fluxes (36.8–38.8 L/(m2·h)) and low permeate conductivity (below 50 μS/cm), increasing the contact angle of the MD membrane by 113 % than that without FO, while the DS using MgCl2 and NH4H2PO4 produced a lower reverse salt flux (0.9–3.2 g/(m2·h)). When diluted DS was treated using PAC, the MD permeate conductivity was further reduced to 35 μS/cm without ammonia, and the membrane hydrophobicity was maintained to 71–83 % of the original. The mechanism of the FDFO-MD integrated process for mitigating MD fouling and improving permeate quality was analyzed, providing guidance for efficient SGPW treatment.

Synergistic effects of microplastics and organic foulants on the performance of forward osmosis membranes

Microplastics (MPs) are emerging contaminants that are abundantly present in the influent and effluent of wastewater treatment plants (WWTPs). Forward osmosis (FO) is an advanced treatment technology with potential applications in WWTPs. The presence of MPs in WWTP effluents can contribute to FO fouling and performance deterioration. This study focuses on FO membrane fouling by MPs of different sizes, and the interactional impacts of MPs and Humic acid (HA) (as the most common organic foulant in WWTPs) on FO membrane performance. The synergistic effect of combined MPs and HA fouling is shown to cause higher flux decline for FO membranes than that of HA or MPs alone. Reverse salt flux increased in the presence of MPs, and decreased when HA was present. Further, full flux recovery was obtained for all fouled membranes after hydraulic cleaning. This indicates the efficiency of FO systems for treating wastewater with high fouling potential. This study highlights the necessity of considering MPs in studying fouling behaviour, and for mitigation strategies of membranes used in WWT. The fundamentals created here can be further extended to other membrane-assisted separation processes.

Molecular level insights into the dynamic evolution of forward osmosis fouling via thermodynamic modeling and quantum chemistry calculation: Effect of protein/polysaccharide ratios

While forward osmosis (FO) shows broad application prospects in wastewater reuse and desalination, it is still hindered by membrane fouling issues. From the perspective of molecular structure and energy, this work investigated the effects of protein (PN)/polysaccharide (PS) ratios of organic foulants on the dynamic evolution of membrane fouling in FO. Fouling tests showed two interesting membrane fouling phenomena: Ⅰ) when PN content increased from 0.2 to 0.8 g/L with fixed PS content of 0.2 g/L, membrane fouling decreased for filtration of the same volume of foulants; Ⅱ) with the increase of filtration volume, the membrane fouling caused by 1:1 PN/PS foulants increased almost linearly, while the membrane fouling caused by 4:1 PN/PS foulants increased significantly at first, and then rapidly reached a stable fouling state. Thermodynamic analyses and quantum chemical calculations revealed that the attractive interaction energy between 1:1 PN/PS foulants and membrane was 1.90 times greater than that for 4:1 PN/PS foulants, and the protein and polysaccharide molecules with a ratio of 1:1 were more likely to form a tight cross-linked structure. Furthermore, the reverse solute diffusion significantly reduced the electrostatic repulsion energy among the polymer chains for 4:1 PN/PS foulants, which induced the transformation of foulant morphology from gel to floc and reduced the adhesion energy to membrane surface by 61%. As a result, in the later fouling stage, few 4:1 PN/PS foulants were newly attached to the membrane, leading to a pseudo-stable flux. Based on the aforementioned findings, this study reveals a unified thermodynamic framework for the effects of the PN/PS ratios of organic foulants on the dynamic evolution of FO membrane fouling. The proposed mechanism is beneficial in formulating “tailored” fouling mitigation strategies and elucidating the appropriate application fields for FO technology.

Molecular Level Insights into the Dynamic Evolution of Forward Osmosis Fouling Via Thermodynamic Modeling and Quantum Chemistry Calculation: Effect of Protein/Polysaccharide Ratios

Molecular Level Insights into the Dynamic Evolution of Forward Osmosis Fouling Via Thermodynamic Modeling and Quantum Chemistry Calculation: Effect of Protein/Polysaccharide Ratios

Reverse osmosis and forward osmosis fouling: a comparison

Our previously reported exploration (Journal of Membrane Science 565 (2018) 241–253) on the differences between fouling in reverse osmosis (RO) and forward osmosis (FO), used alginate as a foulant with initial conditions that ensured that the starting fluxes were the same. That study found that for a cellulose triacetate (CTA) membrane the extent of fouling, based on the analysis of foulant resistance, was greater when the membrane was part of a FO system. Herein, using the same methodology, results for a thin film composite membrane with alginate as the foulant are presented and these confirm the same general conclusion namely that the extent of foulant accumulation in FO mode is more severe than in RO mode. Furthermore the specific fouling resistance with alginate fouling in FO is more than for RO. However examining the overall operation including cleaning as well as fouling, this study suggests that FO operation is potentially less sensitive to fouling phenomena than RO for similar feed materials. This is due to the driving force compensation coming from a changing level of ICP. Some preliminary work including that with silica particles is also reported.

Quantifying the influence of divalent cations mass transport on critical flux and organic fouling mechanism of forward osmosis membrane

Understanding the insightful impact of divalent cations mass transport on the complex organic fouling of forward osmosis (FO) membrane is vital when seawater/brine is utilized in a FO hybrid process. Our works deeply focused on quantifying the influence of divalent cations on not only critical flux but also the organic fouling mechanism. The presence of divalent cations in aqueous solutions caused a decrease in critical flux values. The fouling mechanism is mainly governed by intermolecular and ion-mediated interactions. The findings suggested the interaction of divalent cations with organic matters close to the membrane surface is more noticeable than that in the feed solution. These interactions combined with an operation at the flux ≥30 LMH led to the formation of a compact and cohesive cake layer (4.8–9.1 μm) where the great divalent cations were deposited on membrane surface after 30 h operation (Ca2+: 162.13–256.72 g/m2, Mg2+: 182.60–374.38 g/m2). In contrast, 21 LMH below critical value exhibited minor fouling with a very thin cake layer (0.5 μm) and minimized deposited divalent cations (Ca2+: 79.47 g/m2, Mg2+: 46.65 g/m2). Overall, the extended operation of 30 h suggested 16–21 LMH were threshold values for FO fouling control.

Novel insights into gel layer fouling in forward osmosis process based on thermodynamic analysis: Role of reverse salt diffusion

Membrane fouling in forward osmosis (FO) process is more complicated than pressure-driven membrane process due to the phenomenon of reverse salt diffusion. Gel layer fouling due to reverse salt diffusion of three draw solutions (NaCl, MgCl2 and CaCl2) were investigated from the thermodynamic view in FO process. The reverse-diffused Mg2+/Ca2+ caused more serious gel fouling and flux decline than Na+ at permeate volume of 500 mL. Non-invasive inverted phase-contrast microscope observed that reverse-diffused Mg2+/Ca2+ induced the formation and cross-linking of long sodium alginate chains. Thermogravimetric analysis (TGA) revealed that Mg2+/Ca2+ enhanced the binding ability of bound water to gel chains. From the thermodynamic view, the above changes caused by Mg2+/Ca2+ resulted in that a higher driving force (osmosis pressure difference) was consumed to overcome the chemical potential difference between gel and permeate during FO process, which gave rise to the less driving force and the worse performance. This study provided a new perspective and insight to explain gel fouling in FO process.

Real-time monitoring of forward osmosis membrane fouling in wastewater reuse process performed with a deep learning model

Monitoring fouling behavior for better understanding and control has recently gained increasing attention. However, there is no practical method for observing membrane fouling in real time, especially in the forward osmosis (FO) process. In this article, we used the optical coherence tomography (OCT) technique to conduct real-time monitoring of the membrane fouling layer in the FO process. Fouling tendency of the FO membrane was observed at four distinguished stages for 21 days using a regular membrane cleaning method. In this method, chemical cleaning, which extracts two to three times as much organic matter (OM) as physical cleaning, was used as an effective method. Real-time OCT image observations indicated that a thin, dense, and flat fouling layer was formed (initial stage). On the other hand, a fouling layer with a thick and rough surface was formed later (final stage). A deep learning convolutional neural network model was developed to predict membrane fouling characteristics based on a dataset of real-time fouling images. The model results show a very high correlation between the predicted data and the actual data. R2 equals 0.90, 0.86, 0.92, and 0.90 for the thickness, porosity, roughness, and density of the fouling layer, respectively. As a promising approach, real-time monitoring of fouling layers on the surface of FO membranes and the prediction of fouling layer characteristics using deep learning models can characterize and control membrane fouling in FO and other membrane processes.

Emerging forward osmosis and membrane distillation for liquid food concentration: A review.

As emerging membrane technologies, forward osmosis (FO) and membrane distillation (MD), which work with novel driving forces, show great potential for liquid food concentration, owing to their low fouling propensity and great driving force. In the last decades, they have attracted the attention of food industry scientists in global scope. However, discussions of the FO and MD in liquid food concentration advancement, membrane fouling, and economic assessment have been scant. This review aims to provide an up-to-date knowledge about liquid food concentration by FO and MD. First, we introduce the principle and applications of FO and MD in liquid food concentration, and highlight the effect of process on liquid food composition, membrane fouling mechanism, and strategies for fouling mitigation. Besides, economic assessment of FO and MD processes is reviewed. Moreover, the challenges as well as future prospects of FO and MD applied in liquid food concentration are proposed and discussed. Comparing with conventional membrane-based or thermal-based technologies, FO and MD show outstanding advantages in high concentration rate, good concentrate quality, low fouling propensity, and low cost. Future efforts for liquid food concentration by FO and MD include (1) development of novel FO draw solution (DS); (2) understanding the effects of liquid food complex compositions on membrane fouling in FO and MD concentration process; and (3) fabrication of novel membranes and innovation of membrane module and process configuration for liquid food processing.

Organic fouling in forward osmosis: Governing factors and a direct comparison with membrane filtration driven by hydraulic pressure

The fouling behavior of osmotically-driven forward osmosis (FO) is widely believed to be superior with respect to hydraulic pressure-driven membrane applications, based on a number of experiments reported in the literature. However, experimental confounders often exist, preventing fair comparison between the different processes, one being the deployment of non-comparable membranes. This study systematically investigates the conditions influencing organic fouling in FO and compares the behavior in FO and in a hydraulic pressure-driven process, under equivalent conditions. The same state-of-the-art polyamide FO membranes were used in the tests, which were run with real feed solutions and under varying conditions to observe the effect of initial flux, draw solution, and feed ionic composition. The results suggest that initial flux and calcium have the strongest influence on the extent of flux decline and recovery. The influence of different draw solutions in FO becomes apparent when the flux is relatively low. Analysis of the fouling indices and of the effective driving force, as well as direct observation of membranes following fouling, support the conclusion that the fouling behavior of the FO process is not necessarily better compared to an analogous hydraulic pressure-driven one, especially under relevant operational conditions and when the two processes work with similar fluxes.

Removal of pharmaceuticals by fouled forward osmosis membranes: Impact of DOM fractions, Ca2+ and real water

This study systematically investigated the impact of dissolved organic matters (DOM) fractions, Ca2+, membrane orientation and real water matrix on the membrane fouling and the subsequent pharmaceutical retention in forward osmosis (FO). Ca2+ increased the removal of carbamazepine (CBZ) through steric effect, while it reduced sulfamethoxazole (SMZ) removal due to reduced electrostatic repulsion and enhanced external concentration polarization for three organic foulants. The study of operating mode showed that the pharmaceutical removal in pressure retarded osmosis (PRO) mode were lower than those in FO mode for both the baseline and HA fouling, which was attributed to the concentrative internal concentration polarization caused by long-term accumulation of pharmaceuticals or HA in support layer. In terms of the real water tests, the secondary effluent used as feed solution caused higher hydrophilicity and negative charge of fouled FO membrane, leading to increased removal of pharmaceuticals. Seawater used as draw solution also caused severe fouling in the support layer of FO with humic acid-like material as major foulants, increasing the removal of SMZ because of enhanced steric hindrance and electrostatic repulsion. However, the combined effects of increased adsorption and steric effect resulted in little change for the CBZ removal. This study gave implications on the practical application of FO process for pharmaceutical removal.

Organic Fouling in Forward Osmosis: A Comprehensive Review

Organic fouling in the forward osmosis process is complex and influenced by different parameters in the forward osmosis such as type of feed and draw solution, operating conditions, and type of membrane. In this article, we reviewed organic fouling in the forward osmosis by focusing on wastewater treatment applications. Model organic foulants used in the forward osmosis literature were highlighted, which were followed by the characteristics of organic foulants when real wastewater was used as feed solution. The various physical and chemical cleaning protocols for the organic fouled membrane are also discussed. The study also highlighted the effective pre-treatment strategies that are effective in reducing the impact of organic fouling on the forward osmosis (FO) membrane. The efficiency of cleaning methods for the removal of organic fouling in the FO process was investigated, including recommendations on future cleaning technologies such as Ultraviolet and Ultrasound. Generally, a combination of physical and chemical cleaning is the best for restoring the water flux in the FO process.

Insight into organic fouling behavior in polyamide thin-film composite forward osmosis membrane: Critical flux and its impact on the economics of water reclamation

A strategy of using critical fluxes to control organic fouling of polyamide thin film composite (PA-TFC) forward osmosis (FO) membranes during wastewater reclamation was developed for FO mode. This work was a comprehensive investigation with various organic foulants covering complex mixtures as well as single foulants. The foulants were alginate (ALG), Humic acid (HA), and Bovine Serum Albumin (BSA) and the study covered different concentration (40; 80; 120; 160 mg/L). Our results indicated that there was a single value of critical flux, 35 LMH for 160 mg/L and single foulant. However the presence of mixed foulants i.e., ALG + BSA, ALG + HA, HA + BSA, at an overall foulant concentration of 160 mg/L gave rise to foulant-foulant-membrane interactions that caused a significant decrease in critical flux values to 25–30 LMH. Using these results as a guide, long-term tests in which there was no fouling or negligible fouling were successfully implemented. Operating below critical flux maintains a sustainable operation with the characteristic of full reversibility, which is vital if chemical cleaning is to be minimized. Characterization of fouling around critical values was made through physico-chemical analyses including SEM, EEM, aggregate size, zeta potential, and FTIR. It was found that FO fouling became irreversible when operated at a flux ≥35 LMH for single foulants and fluxes of 25 LMH and 30 LMH for ALG + BSA and HA + BSA foulants respectively, being a foulant concentration of 160 mg/L; such conditions are favorable for the formation of the cohesive and compact cake layer. Economic assessments based on specific energy consumption facilitated the production of guidelines for practical design and operation.

Characterization of colloidal fouling in forward osmosis via ultrasonic time- (UTDR) and frequency-domain reflectometry (UFDR)

Ultrasonic time- (UTDR) and frequency-domain reflectometry (UFDR) were applied to characterize internal and external fouling in the forward osmosis (FO) process. Unlike RO applications, in which the transducer was placed above the membrane to detect external fouling on the top surface of membrane, the transducer was placed below the membrane to enable detection of internal and external fouling in an FO application. The amplitude changes and arrival-time shifts in UTDR were more sensitive than the flux decline as an indicator of FO fouling. In the active-layer facing the feed solution (AL-FS) mode, the cake-layer thickness obtained via the differential UTDR signal agreed well with the mass-balance data. The Short-Time-Fourier-Transform (STFT) analysis permitted decomposing the non-overlapping peaks that revealed a significant decrease in the amplitudes of the high-frequency components due to the grain-scattering effect in the active-layer facing the draw solution (AL-DS) mode. In contrast, the frequency distribution remained unchanged in the AL-FS mode. The total reflected power (TRP) calculations for the arrival-times and principal peaks in the frequency-domain correlated well with the overall fouling and internal fouling, respectively.

Quantitative analysis of the irreversible membrane fouling of forward osmosis during wastewater reclamation: Correlation with the modified fouling index

In this study, the fouling behavior in the long-term performance of the forward osmosis (FO)-based osmotic dilution process was systematically explored by assessing the impact of irreversibility. The effects of physical cleaning, scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analyses, and foulant distributions were systematically investigated to control irreversible organic foulants on the membrane surface. It was observed that specific foulants in the secondary wastewater effluent impeded the long-term performance of FO fouling reversibility and final flux. A strong correlation between irreversible foulant concentrations, especially that of protein-like biopolymer, and physical fouling reversibility was observed, which caused continual irreversible fouling in the FO process. Multiple modified fouling indexes (MFIs) were measured to evaluate the fouling potential of the feed water with size fractionation. It was confirmed that the MFI-UF employing a 300 kDa ultrafiltration (UF) membrane is an appropriate water quality index for studying irreversible membrane fouling. It is expected that the application of MFI in predicting the fouling potential of FO intake water will significantly contribute toward the development of operational guidelines for FO plants.

Conductive thin film nanocomposite forward osmosis membrane (TFN-FO) blended with carbon nanoparticles for membrane fouling control

Membrane fouling in forward osmosis (FO) significantly affects water flux and membrane life, which restricts the further development of FO. In this work, carbon nanoparticles were blended in polyethersulfone (PES) to prepare a conductive thin film nanocomposite (TFN) FO membrane to control the membrane fouling in FO processes. The membrane containing 4 wt% carbon exhibited an optimum performance with water flux of 14.0 and 17.2 LMH for FO (active layer for FS) and PRO (active layer for DS) modes, respectively, using DI water as feed solution and 1 M NaCl as draw solution and electrical conductivity of 170.1 mS/m. Dynamic antifouling experiments showed that, compared with no voltage applied, the water flux decline of surface charged TFN-FO membrane was significantly retarded. For CaSO4, BSA and LYS as model contaminants, the water fluxes were improved by 31%, 13% and 7% under the voltages of +1.7 V, −1.7 V and +1.7 V, respectively. Moreover, the charged membrane is more effective in relieving the initial membrane fouling, and contaminant-contaminant interactions mechanism dominates the formation of further membrane fouling processes. Therefore, for contaminants with different charge conditions, customizing membrane surface charges is a feasible and promising approach for controlling membrane fouling in situ method.

Effect of the coagulation/persulfate pre-treatment to mitigate organic fouling in the forward osmosis of municipal wastewater treatment

The forward osmosis (FO) membrane process has recently established in many applications such as desalination, wastewater reuse, water purification, food processing, resource recovery and sustainable power generation. However, many researchers raise the demand for systematic investigation on FO membrane fouling, which leads to reduced flux yield. In this study, the effect of coagulation/persulfate as a feed pre-treatment was used to mitigate FO organic fouling during municipal wastewater treatment, and compared with a control coagulation and potassium persulfate pre-treatments. Mass balance results using size exclusion chromatography exhibited that the decrease in the flux with consecutive filtration cycles was likely due to humic-like molecules in the feedwater. Coagulation/persulfate contributed to a more significant flux improvement than stand-alone coagulation or persulfate pre-treatment, resulting in a smaller amount of organics attachment to the membrane. A better flux enhancement by coagulation/persulfate was again evidenced by a higher decrease in the attachment of reversible and irreversible organic foulants on the membrane surface. This study identified the major organic components responsible for FO fouling and established the potential of coagulation/persulfate pre-treatment for reducing organic fouling of FO membrane during municipal wastewater treatment.

In situ extracting organic-bound calcium: A novel approach to mitigating organic fouling in forward osmosis treating wastewater via gradient diffusion thin-films

Forward osmosis (FO) has gained increasing interests in wastewater treatment and reclamation. However, membrane fouling has become one major obstacle hindering FO application. A novel mitigation approach for FO membrane fouling via in situ extracting Ca2+ binding with the organic foulants using the gradient diffusion thin-films (DGT) was proposed in this study. The DGT could effectively adsorb the Ca2+ binding with the sodium alginate via the chelation of the Chelex functional groups, and its adsorption amount of Ca2+ correspondingly increased as a function of the Ca2+ concentration in the feed solution. Owing to the extraction of Ca2+ from the fouling layer by the DGT, the FO membrane fouling was effectively mitigated evident by significant enhancement of water flux, and at the same time, foulants became easily removed by physical cleaning. The alleviation of FO membrane fouling by the DGT could be attributed to the fact that the structure of the fouling layer became more porous and looser after in situ removing Ca2+ from the alginate-Ca2+ gel networks. The feasibility of fouling control strategy via in situ removing Ca2+ binding with the foulants in the fouling layer was demonstrated, which provides new insights into fouling control mechanisms during FO treating wastewater.

Experimental investigation into the use of sodium nitroprusside for controlling polysaccharide fouling in membrane separation

Biofouling has been regarded as a great challenge in membrane separation processes, such as reverse osmosis (RO) and forward osmosis (FO). One of the major contributors to biofouling is the extracellular polymeric substances (EPS) produced by bacteria, especially the polysaccharides that form a large part of EPS. This study investigated experimentally the inhibition of polysaccharide fouling by sodium nitroprusside (SNP) in RO and FO using two model polysaccharides, alginate and xanthan. It was hypothesized that NO released from SNP would act as a free radical to decompose polysaccharides and in turn alleviate fouling in membrane separation. Potassium ferricyanide (KFCN), having a similar structure as SNP, was used as a comparison. The results showed that SNP could alleviate polysaccharide fouling and its efficiency was greater than KFCN in reducing polysaccharide fouling of RO, likely due to the NO radical released. The presence of Ca2+ ions in feedwater increased the extent of fouling by both alginate and xanthan, but SNP was able to alleviate the fouling. Alleviation of polysaccharide fouling in FO was better than in RO under comparable operating conditions. SNP could be considered as a polysaccharide fouling alleviating agent.