ArticleLiterature Review

Tackle Reverse Solute Flux in Forward Osmosis towards Sustainable Water Recovery: Reduction and Perspectives

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Forward osmosis (FO) has emerged as a potentially energy-efficient membrane treatment technology to yield high-quality reusable water from various wastewater/saline water sources. A key challenge remained to be solved for FO is reverse solute flux (RSF), which can cause issues like reduced concentration gradient and loss of draw solutes. Yet no universal parameters have been developed to compare RSF control performance among various studies, making it difficult to position us in this “battle” against RSF. In this paper, we have conducted a concise review of existing RSF reduction approaches, including operational strategies (e.g., pressure-, electrolysis-, and ultrasound-assisted osmosis) and advanced membrane development (e.g., new membrane fabrication and existing membrane modification). We have also analyzed the literature data to reveal the current status of RSF reduction. A new parameter, mitigation ratio (MR), was proposed and used together with specific RSF (SRSF) to evaluate RSF reduction performance. Potential research directions have been discussed to help with future RSF control. This review intends to shed more light on how to effectively tackle solute leakage towards a more cost-effective and environmental-friendly FO treatment process.
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... However, the performance of FO system is still hampered by solute buildup and membrane fouling (Akther et al., 2015;Cath et al., 2006). For asymmetric TFC-FO membranes, solute buildup is usually caused by the concentrated feed solutes owing to the high rejection of active layer and the diffusion of draw solutes into the feed when the active layer faces the feed solution (Morrow and Childress, 2019;Zou et al., 2019). The solute buildup will cause a drastic loss in the effective osmotic driving force for water transport and further lead to a flux decline (Hancock and Cath, 2009). ...
... When the vibration was applied, the J w increased while the J s decreased (Fig. 2), suggesting that the vibration reduced the RSF and improved the water flux of the tested TFC-FO membranes. These results might be attributed to the increase in flow velocity of water and NaCl solution on the surface of TFC-FO membrane caused by the vibration (Zou et al., 2019). ...
... The bright blue closed to the FO membrane in the feed solution side indicated that there existed solute buildup of NaCl in feed solution. The solute buildup, mainly consisting of RSF and concentrating effect by FO membrane rejection (Zou et al., 2019), could reduce the effective driving force and further cause a flux decline . Permeating water did not diffuse well into the draw solution under low cross-flow velocity conditions, because the RSF from the draw solution and the solute in the feed solution were concentrated on the surface of the active layer (Suh and Lee, 2013). ...
Article
Forward osmosis (FO) is limited by solute buildup and membrane fouling. Although current solutions (e.g., influent pretreatment and membrane modification) have partially compensated these drawbacks, they are still enslaved to the uncertainties and costs from the complex operational requirements and large use of chemicals. Therefore, developing simply-operated and chemical-free methods is highly required. In this work, a lab-scale vibrating FO device was constructed and its water permeability and anti-fouling capacity were evaluated. The results of flux tests show that the vibration could effectively enhance the water flux and mitigate solute buildup, mainly resulted from changing the flow field on the membrane surface through the computational fluid dynamic simulations. In addition, the vibrating FO was also proven to be effective in controlling the fouling caused by model organic foulants like bovine serum albumin, humic acid, alginate, and biofouling by different ways. The results of anti-fouling tests and fouling characteristics show that the organic fouling was alleviated by disintegrating the fouling layer and reducing the solute buildup, while the biofouling was mitigated through retarding the early microbial attachment and growth. This work provides a feasibility of applying vibration as an effective strategy to control solute buildup and fouling in FO systems.
... Forward osmosis (FO) as an emerging water and wastewater treatment technology has gained increasing attention (Cath et al., 2006;Zhao et al., 2012;Chung et al., 2012;Shaffer et al., 2015;Zou et al., 2019;Lee and Hsieh, 2019). In contrast with traditional hydraulic pressure driven membrane processes, FO takes advantage of natural osmotic pressure for solute-water separation and shows merits in reducing energy input, lowering membrane fouling and producing high quality product water (Lutchmiah et al., 2014;McGovern et al., 2014;Awad et al., 2019). ...
... In contrast with traditional hydraulic pressure driven membrane processes, FO takes advantage of natural osmotic pressure for solute-water separation and shows merits in reducing energy input, lowering membrane fouling and producing high quality product water (Lutchmiah et al., 2014;McGovern et al., 2014;Awad et al., 2019). As a result, FO is considered a promising alternative in brackish and sea water desalination, water purification and energy recovery (Logan and Elimelech, 2012;Shaffer et al., 2015;Zou et al., 2019). In the area of wastewater treatment, FO has been proposed for direct sewer mining (Xie et al., 2013;Zhang et al., 2014), nutrient concentration and recovery (Xie et al., 2014;Qiu et al., 2015;Ansari et al., 2017;Volpin et al., 2019), and water recovery from wastewaters for irrigation (Phuntsho et al., 2012;Chekli et al., 2016). ...
... However, unlike RO, separation in FO relies on osmotic pressure, which is driven by a draw solution Ge et al., 2013;Shaffer et al., 2015;Lee and Hsieh, 2019). Apart from the forward transport of solute from the feed to the draw solution, draw solutes also inevitably leak from the draw solution into the feed (Achilli et al., 2010;Hancock et al., 2011;Zou et al., 2019); this phenomenon is typically termed as "bidirectional transport (or diffusion) of solutes" (Hancock et al., 2011;Lu et al., 2014). When the feed and draw solutes are electrolytes, their interactions may mutually affect their transport behaviors. ...
Article
Electrolytes are commonly employed as draw solutes in forward osmosis (FO). This work demonstrates that electrostatic interactions play a key role in ion transport in the FO process. The difference in diffusivity between the constituent ions of the draw electrolyte significantly impact the forward transport of the feed ions. Draw electrolyte composed of low-diffusivity cations and high diffusivity anions promoted forward transport of the feed anions and retarded that of the feed cation, and vice versa. The effects were remarkable even for the most commonly used draw electrolytes (NaCl or MgCl2), where the forward flux of NO3− and NO2− was found to increase by a few folds and that of NH4+ was reduced by similar magnitudes than that observed in a nonelectrolyte draw solute (glucose) system. More profound increase/reduction (up to 10 times) was observed for draw electrolytes composed of highly asymmetric cations and anions. An analytical model is developed by considering the electrostatic interaction between the draw and the feed ions, to predict its effect on the forward transport of the feed ions. The normalized diffusivity difference (θD) between the constituent ions of the draw electrolyte is found as a key factor that determines the transport behaviors of the feed ions. These results may have important implications in enhancing our understanding of bidirectional ion transport in FO. The findings may also be useful in the design and development of FO processes for enhanced removal of charged pollutants via draw solute selection and formulation.
... Forward osmosis (FO) as an emerging water and wastewater treatment technology has gained increasing attention (Cath et al., 2006;Zhao et al., 2012;Chung et al., 2012;Shaffer et al., 2015;Zou et al., 2019;Lee and Hsieh, 2019). In contrast with traditional hydraulic pressure driven membrane processes, FO takes advantage of natural osmotic pressure for solute-water separation and shows merits in reducing energy input, lowering membrane fouling and producing high quality product water (Lutchmiah et al., 2014;McGovern et al., 2014;Awad et al., 2019). ...
... In contrast with traditional hydraulic pressure driven membrane processes, FO takes advantage of natural osmotic pressure for solute-water separation and shows merits in reducing energy input, lowering membrane fouling and producing high quality product water (Lutchmiah et al., 2014;McGovern et al., 2014;Awad et al., 2019). As a result, FO is considered a promising alternative in brackish and sea water desalination, water purification and energy recovery (Logan and Elimelech, 2012;Shaffer et al., 2015;Zou et al., 2019). In the area of wastewater treatment, FO has been proposed for direct sewer mining (Xie et al., 2013;Zhang et al., 2014), nutrient concentration and recovery (Xie et al., 2014;Qiu et al., 2015;Ansari et al., 2017;Volpin et al., 2019), and water recovery from wastewaters for irrigation (Phuntsho et al., 2012;Chekli et al., 2016). ...
... However, unlike RO, separation in FO relies on osmotic pressure, which is driven by a draw solution Ge et al., 2013;Shaffer et al., 2015;Lee and Hsieh, 2019). Apart from the forward transport of solute from the feed to the draw solution, draw solutes also inevitably leak from the draw solution into the feed (Achilli et al., 2010;Hancock et al., 2011;Zou et al., 2019); this phenomenon is typically termed as "bidirectional transport (or diffusion) of solutes" (Hancock et al., 2011;Lu et al., 2014). When the feed and draw solutes are electrolytes, their interactions may mutually affect their transport behaviors. ...
... seawater) are not available (Blandin et al., 2015;Corzo et al., 2017). The RSF depends on many factors such as FO membrane properties, operational conditions and solute characteristics (Zou et al., 2019). The development of new FO membranes has gained special attention to improve FO membrane performance (Blandin et al., 2015;Lee and Hsieh, 2019;Zhao et al., 2012). ...
... The development of new FO membranes has mainly focused on improving water flux. However, little attention has been given to develop FO membranes able to achieve high water fluxes while minimising the RSF (Zou et al., 2019). Most research efforts have focused on (i) reducing ICP effects by modifying the porosity, tortuosity and hydrophilicity of the support layer and (ii) increasing water permeability by modifying membrane characteristics of the active layer (Blandin et al., 2015;Tiraferri et al., 2013). ...
Article
This research evaluated the performance of a lab-scale anaerobic membrane bioreactor (AnMBR) treating municipal sewage pre-concentrated by forward osmosis (FO). The organic loading rate (OLR) and sodium concentrations of the synthetic sewage stepwise increased from 0.3 to 2.0 g COD L⁻¹ d⁻¹ and from 0.28 to 2.30 g Na⁺ L⁻¹ to simulate pre-concentration factors of 1, 2, 5 and 10. No major operational problems were observed during AnMBR operation, with COD removal efficiencies ranging between 90 and 96%. The methane yield progressively increased from 214 ± 79 to 322 ± 60 mL CH4 g⁻¹ COD as the pre-concentration factor increased from 1 to 10. This was mainly attributed to the lower fraction of methane dissolved lost in the permeate at higher OLRs. Interestingly, at the highest pre-concentration factor (2.30 g Na⁺ L⁻¹) the difference between the permeate and the digester soluble COD indicated that membrane biofilm also played a role in COD removal. Finally, a preliminary energy and economic analysis showed that, at a pre-concentration factor of 10, the AnMBR temperature could be increased 10 °C and achieve a positive net present value (NPV) of 4 M € for a newly constructed AnMBR treating 10,000 m³ d⁻¹ of pre-concentrated sewage with an AnMBR lifetime of 20 years.
... NaCl, KCl) have been widely used as draw solutes because they feature high diffusivities and mitigate the detrimental effect of internal concentration polarisation (ICP) on water flux (Lutchmiah et al., 2014;Shaffer et al., 2015). However, these solutes generally feature high reverse solute fluxes (RSF) due to their high diffusivity (Zou et al., 2019). The RSF from the draw to the feed solution: (i) increases the salinity of the sewage and (ii) increases the draw solution replenishment costs (Ferby et al., 2020). ...
... Furthermore, high RSFs could enhance biofouling and scaling on FO active layer due to the interaction of the sewage compounds with the draw solute cations (i.e. Na + , Ca 2+ , Mg 2+ ) (She et al., 2012;Zou et al., 2019). These results illustrate that the selection of a suitable draw solute for FO + AnMBR system requires a compromise solution considering the capability of the draw solute to achieve high water fluxes with limited RSF. ...
Article
This research investigated the impact of draw solute and membrane material on the economic balance of a forward osmosis (FO) system pre-concentrating municipal sewage prior to an anaerobic membrane bioreactor (AnMBR). Eight and three different draw solutes were evaluated for cellulose triacetate (CTA) and polyamide thin film composite (TFC) membranes, respectively. The material of the FO membrane was a key economic driver since the net cost of TFC membrane was substantially lower than the CTA membrane. The draw solute had a moderate impact on the economic balance. The most economically favourable draw solutes were sodium acetate and calcium chloride for the CTA membrane and magnesium chloride for the TFC membrane. The FO + AnMBR performance was modelled for both FO membrane materials and each draw solute considering three FO recoveries (50, 80 and 90%). The estimated COD removal efficiency of the AnMBR was similar regardless of the draw solute and FO membrane material. However, the COD and draw solute concentrations in the permeate and digestate increased as the FO recovery increased. These results highlight that FO membranes with high permselectivity are needed to improve the economic balance of mainstream AnMBR and to ensure the quality of the permeate and digestate.
... The nutrient loss from the DS due to reverse diffusion is a critical challenge in FDFO; optimizing operational conditions, developing advanced membranes, and selecting the appropriate fertilizer DS can reduce reverse solute flux (RSF). 12,13 The filtration and cleaning behaviors of FO membranes are also influenced by membrane orientation. 9,14 The water quality for irrigation greatly influences physiological and biological characteristics and crop yields. ...
... Compared to fouling, RSF may be a more problematic issue, causing loss of the valuable DS (i.e., nutrients in FDFO), reduced concentration gradient, increased fouling propensity, and increased difficulty in feed brine management. 13,50 As shown in Figure 2A,B, the DS using week of growth. Note, the increase in weight (i.e., the difference of final weight and seed weight) was used as the y-axis, while the average weight of Cherry radish and Chinese cabbage seed was 11.4 and 3.5 mg, respectively; DI, deionized water; FPW5000, FPW1000, FPW700, and FPW350, diluted FPW with TDS of 5000, 1000, 700, and 350 mg·L −1 , respectively; DS1000, DS700, and DS350, the diluted DS with TDS of 1000, 700, and 350 mg·L −1 . ...
Article
Fertilizer drawn forward osmosis (FDFO) was proposed to extract fresh water from flowback and produced water (FPW) from shale gas extraction for irrigation, with fertilizer types and membrane orientations assessed. Draw solution (DS) with NH4H2PO4 displayed the best performance, while DS with (NH4)2HPO4 resulted in the most severe membrane fouling. DS with KCl and KNO3 led to substantial reverse solute fluxes. FDFO operation where the active layer of the membrane was facing the feed solution outperformed that when the active layer was facing the DS. Diluted DS and diluted FPW samples were used for irrigation of Cherry radish and Chinese cabbage. Compared to deionized water, irrigation with diluted DS (total dissolved solid (TDS) = 350 mg·L-1) promoted plant growth. In contrast, inhibited plant growth was observed when FPW with high salinity (TDS = 5000 mg·L-1) and low salinity (TDS = 1000 mg·L-1) was used for irrigation of long-term (8-week) plant cultures. Finally, upregulated genes were identified to illustrate the difference in plant growing. The results of this study provide a guide for efficient and safe use of FPW after FDFO treatment for agricultural application.
... J s plays a fundamental role in the design of osmotically driven processes (Phillip et al., 2010), since it decreases the osmotic driving force (Phuntsho et al., 2011), represents economic losses (fertilizer losses in FDFO) and causes difficulties with feed concentrate management (Phuntsho et al., 2013), hence jeopardizing the benefits of the FO process (Chekli et al., 2012). As pointed out by Zou et al. (2019) in a review of approaches to reduce reverse solute fluxes in FO, it is crucial for FO operations to control and reduce J s , and they also highlighted the lack of J s data in FO studies. Therefore, detailed studies of solute fluxes in FO are of great interest to assess their impact on FO performance. ...
... However, we consider that this approach would increase the costs and make the process more complex. Zou et al. (2019) pointed out the need of system optimization, membrane development, long term evaluation, as well as other cost-effective strategies to reduce the reverse salt fluxes in FO, which is crucial for a proper FO operation. In the same line, our results point out the need to evaluate nutrient losses when regard to DS dilution close to real conditions of the FDFO application. ...
Article
Full-text available
There is a need for water reuse technologies and applications to minimize the imminent water crisis, caused by the world population growth, the reduction of freshwater resources and the increasing water pollution. Fertilizer-drawn forward osmosis (FDFO) is a promising process capable of simultaneously extracting fresh water from low-quality sources as feed water (e.g., wastewater or greywater), while diluting fertilizer solutions for direct fertigation, avoiding the demand for freshwater for irrigation. Achieving an adequate level of dilution for direct fertigation is a key element to be evaluated for the implementation of FDFO. This study assessed the performance of the forward osmosis process to dilute fertilizer solutions to be applied directly in hydroponic systems. Experiments were carried out under conditions close to osmotic equilibrium to evaluate the process performance up to the maximum dilution point. Tests were carried out with individual and blended fertilizers (i.e., (NH4)2HPO4 or DAP, and KNO3) used as draw solution (DS) and with deionized water or individual salts (NaCl, MgCl2, Na2SO4, MgSO4) in the feed solution (FS). Water fluxes and reverse salt fluxes indicated that both fertilizer DS composition and concentrations play a fundamental role in the process. Suitable nutrient concentrations to be directly applied without further dilution for N, P and K (119, 40, 264 mg.L⁻¹ respectively) were obtained with deionized water as FS and blended DAP (0.025 M) and KNO3 (0.15 M) as DS. However, important fertilizer losses from DS to FS were observed, being the highest for NO3⁻ (33–70% losses from DS to FS). The presence of salts in FS decreased the water fluxes and the DS dilution due to the osmotic equilibrium caused by a greater loss of nutrients from DS to FS (up to 100%), compared with tests using just deionized water as FS. This study points out the potential limitations of the FDFO process, due to the high solute fluxes and low water fluxes in conditions close to osmotic equilibrium.
... However, existing TFC membrane modifications are usually carried out from the SL and AL, respectively, the major limitation is that the improvement of water flux and selectivity of TFC membranes cannot be taken into consideration simultaneously [31,32]. This paper fabricates the novel Turing structures in the AL of TFC membrane through effectively introducing the PVP macromolecule with hydrophilicity both in the SL and AL. ...
Article
Full-text available
Improving the performance of forward osmosis (FO) membranes has always been moving forward. Here we fabricate the novel Turing structures in the active layer (AL) of thin film composite (TFC) membrane through effectively introducing the polyvinylpyrrolidone (PVP) macromolecule with hydrophilicity both in the support layer (SL) and AL. The addition of PVP facilitates the formation of sponge-like pores in the SL and stripe-like Turing structures in the AL. The influence of PVP on the morphology and performance of the membranes was investigated by SEM, AFM, XPS, NMR, FTIR. Compared with the water flux (Jw) of the original composite membrane (approximately 25 L m⁻² h⁻¹), TFC-PVP (3:1) membrane with Turing structure achieved better performance (approximately 75 L m⁻² h⁻¹), and the reverse solute flux/water flux (Js/Jw) value was as low as 0.02 g/L. This study demonstrated that the Turing structures have a favorable effect on the performance of FO membrane and a promisingly practical application in water treatment. Graphic abstract
... Benchmark experimental results showed that Module 2 has ≈4x higher flux compared to Module 1. This is in agreement with previous studies showing that TFC membranes have higher water permeability compared to CTA due to different chemistry properties [56,71,72]. Also, the flux obtained experimentally was within 5 % the model predictions (Fig. 9). ...
Article
Full-text available
Osmotic concentration (OC), a form of forward osmosis (FO) but without draw solution recovery, can be applied for reducing wastewater disposal volumes in the oil & gas industry. Within this industry, wastewater is often disposed of by injection through disposal wells into deep underground reservoirs. By reducing wastewater disposal volumes, the sustainability of the disposal reservoir is improved. In this application of OC, seawater or brine from a desalination plant serves as the draw solution and the diluted seawater is discharged to the sea. This study compared 3 commercial hollow-fiber FO membranes (CTA, TFC, aquaporin proteins) for reducing the volume of low salinity wastewater generated during liquified natural gas (LNG) production. Additionally, a model was developed to predict the performance of commercial full-scale membranes by identifying optimum operating conditions, taking into consideration the trade-off between feed concentration factor and water flux. Bench-scale tests were conducted using synthetic and actual wastewater from an LNG facility to evaluate OC technology performance and validate model predictions. Based on model results with a feed mimicking the salinity of actual wastewater, a 4x concentration factor produced a reasonable compromise between feed recovery and draw solution dilution and was considered the optimum for future tests. At higher concentration factors, the increased dilution of the draw solution negatively impacted flux. In bench tests with real wastewater, the TFC chemistry had a ≈5x higher water flux (9.7 vs. 1.9 L/m²-h) and a ≈3x lower specific reverse solute flux (192 vs. 551 mg/L) compared to the CTA chemistry. However, both membranes showed less than 5% fouling and a specific forward organic solute flux of less than 0.5 mg/L of total organic carbon (TOC). Pilot testing for >50 h showed stable performance, comparable to bench scale data and model predictions.
... Recent developments in MSPs have demonstrated that emerging processes, such as forward osmosis (FO), are a potential and effective alternative for water reclamation [5]. Contrary to conventional MSPs, FO is osmotically driven, which leads to a low fouling rate [6,7]. Several attempts have been made to combine the FO technology with membrane bioreactors. ...
Article
A novel configuration of an osmotic anaerobic membrane bioreactor coupled with membrane-assisted distillation (OMBR-MD) in a single submerged module was proposed for domestic sewage treatment and potabilization. A steady permeate flux was achieved after the 22nd day of monitoring, in which the draw solution (DS) was diluted by the forward osmosis (FO) permeate at the same rate in which it was concentrated by the membrane distillation (MD). Salinity build-up inside the bioreactor contributed to fouling in the FO membrane since it increases the production of soluble microbial products and extracellular polymeric substances. In addition, organic matter accumulated in DS, due to the closed-loop system, may be the main cause for fouling in MD membranes at the latter stages. The OMBR-MD presented great removal for organic matter (91%), phosphorous (95%) and ammonium nitrogen (71%). Alkalinity accumulation within the bioreactor prevented a significant change in bulk solution pH (8.0 – 8.4), reducing the effects of volatile fatty acids production on methanogenic performance. The OMBR-MD removal efficiencies were higher than 96% for all 7 selected pharmaceutical drugs. Additionally, the MD distillate attained eight out of the nine parameters assessed for potable water standards established in Brazilian legislations and recommendations from US EPA, including Escherichia coli. Therefore, the novel OMBR-MD proved to be a feasible alternative for treating municipal wastewater, generating a high-quality distillate.
... Indeed, an alteration of membrane transport properties in the pressure-driven operation was explored from the past studies [16,43,44]. On another side, in regard to draw solute loss minimization, some externally assisted methods has been reported to possibly pose a risk of physicochemical alteration., for instance, applying high voltage in electro-assisted osmosis (EAO) and ultrasound in ultrasound-assisted osmosis (UAO) [45]. Therefore, to suggest an additional insight for the solute loss mitigation, J s /J w ratio was analyzed by quantifying the effect of cross-flow velocity for hydrodynamic evaluation and surface charge for surface modification consideration. ...
Article
Perm-selectivity consisting of water flux Jw and solute flux Js or in form of Js/Jw ratio is an important parameter of designing Forward Osmosis (FO) membrane as it indicates the membrane performance and how much solute replenishment over the extracted pure water from the feed solution. Parameter Js/Jw ratio is dependent on hydrodynamic condition i.e cross-flow velocity (CFV), solute type i.e. diffusivity, trans-membrane surface potential. This study employed Cellulose Triacetate (CTA) membrane for representing low-charge membrane and Polyamide-Thin Film Composite (PA-TFC) for the membrane of highly negative surface charge. Six (6) different models were used to quantify the effect of external mass transfer, the ideal solution, non-ideal solution, trans-membrane surface potential on the transport of solute across the membrane. Our new model was proven to improve the prediction of perm-selectivity. The improvement was attributed to the application of trans-membrane potential-dependent solute partitioning for solute permeability correction and the application of experimentally obtained mass transfer coefficient. By the incorporation of the Donnan effect in determining the transmembrane potential, it was found that in the low charge membrane namely CTA, the dominant transport mechanism was diffusion, while in a highly negative surface charged membrane namely TFC, the partition of solute to be the dominant mechanism. Operation at a low CFV posed less impact of the membrane charge. The newly developed model provided a good foundation for FO process design under different CFVs and modified surface charges.
... Considering the progressive growth of population and the limitation of the world freshwater reserves, rapid and economical desalination of saline/brackish water and treatment of wastewater have become increasingly important to provide clean water for different purposes [1][2][3][4]. Currently, reverse osmosis (RO) has a wide range of applications in water treatment processes due to its superiority over the other conventional methods [5][6][7][8]. Nevertheless, the energy consumption of RO is still high despite the remarkable progresses and many efforts made during the past several decades to reduce it, due primarily to the intrinsic thermodynamic constraints of the membrane desalination process [6]. Hence, the minimum amount of energy required for complete separation is at least equal to or greater than the free enthalpy of mixing [9]. ...
Article
Recently, forward osmosis (FO) has attracted a great deal of attention in desalination and wastewater treatment. Nevertheless, there are several critical challenges such as the need for new advances in designing membranes that must be met to enhance the water flux in FO processes, control the reverse salt flux, concentration polarization and fouling. Therefore, designing a suitable membrane with a high-water flux, low reverse salt flux, low fouling, and controlled concentration polarization seems to be essential. Thin film composite (TFC) membranes are the most widely used membranes in the FO field. Extensive research has been performed to fabricate and design high performance TFC membranes which can be exclusively used in FO processes. This paper aims to review three types of TFC membranes i.e. TFC's with polyamide active layer (TFC-A), thin film nanocomposites (TFC-N) and double-skinned TFC membranes (TFC-D) in flat sheet and hollow fiber configuration. Finally, an attempt is made to generate a general performance curve based on the water flux and reverse salt flux of these three TFC FO types and the future direction of the R and D on the FO membrane are discussed.
... When the organic solute flux is normalized by the water flux, the normalized organic flux value was 0.9. These results are in agreement with published data for CTA FO membranes (Sauchelli et al., 2018;Zou et al., 2019). ...
Article
Full-text available
The current article tackles the challenge of reducing wastewater volumes generated from the gas industry. A forward osmosis (FO) pilot unit, deployed as osmotic concertation (OC) process without the draw solution (DS) recovery step, was applied as an option for volume reduction of real industrial effluents. A commercial hollow fiber (HF) FO membrane fabricated from Cellulose Triacetate (CTA) was firstly tested with synthetic feed solution (FS) to investigate the separation properties of the membrane and to identify the optimum operating conditions of the pilot unit. The pilot plant was then challenged with real industrial wastewater for an extended period of operation, primarily to assess membrane-fouling propensities and other performance parameters. Results revealed that according to the operating conditions, the CTA membrane can achieve feed recoveries between 60%–90%, at water fluxes between 2.24-1.65 L.m⁻².h⁻¹ (LMH)). The operation at 75% feed recovery was identified as the optimum condition since it showed the lowest specific solute flux (20.93 mmol.L⁻¹) at a water flux of 1.94 LMH. Outcomes of pilot testing with the real wastewater demonstrated operational stability for over 50 h of continuous operation. The pilot system recovered 75% of the wastewater feed at a stable flux trend with minimal flux decline. Water flux of 1.76 LMH was recorded along with reverse solute flux of 292 mmol.h⁻¹. The water flux was observed to decline slightly by only 5.6%, which was attributed to inorganic scaling on the membrane surface where cleaning with citric acid solution demonstrated efficacy in restoring the initial flux.
... A suitable membrane for FO process must exhibit among others a high hydrophilic character, a high water permeance, a highly selective thin layer with a support having a low tortuosity factor and a high porosity [31]. Maximizing the permeate water flux while minimizing the reverse solute permeate flux that causes a decline of the transmembrane osmotic pressure gradient is one of the proposed objectives in FO membrane engineering [32]. Various types of membranes were developed to optimize FO separation process [25,33,34]. ...
Article
An alternative use of end-of-life reverse osmosis (RO) membranes is proposed for forward osmosis (FO) application as recycled FO (RFO) membranes and transformed recycled FO (TRFO) membranes. Different passive cleaning protocols in pilot plant and laboratory scale were followed using sodium hypochlorite (NaClO) at different concentrations and exposure time. The RFO with the best performance was selected for its transformation by interfacial polymerization (IP) technique to improve further the FO performance. Both the morphological structure and transport properties of the RFO and TRFO membranes were studied by means of different characterization techniques. Although the RFO membranes are suitable for FO, the TRFO membranes are more competitive. The highest FO water permeate fluxes (12.21 kg/m²·h and 15.12 kg/m²·h) were obtained for the membrane recycled applying the highest NaClO exposure dose applied in pilot plant (10⁶ ppm·h) followed by IP of a thin polyamide layer. These permeate fluxes were better or at least comparable to commercial membranes used under the same FO conditions. The results indicated that it is possible to use discarded RO membranes in FO technology for wastewater treatment after adequate treatment procedures extending their lifetime and contributing to a circular economy and sustainability in membrane science and related materials.
... The ratio of Js and Jw is characterized as the specific reverse salt flux and effectively decreasing its value is the main challenge in FO membrane development. Surface coating is one of the most effective methods for membrane modification to obtain low reverse salt fluxes, high water fluxes, hydrophilicity, and antifouling properties [16]. Dopamine and polydopamine (PDA) (Figure 1) have gained great attention as thin surface coatings due to material-independent surface adhesion and antifouling properties. ...
Article
Full-text available
Application of forward osmosis (FO) is limited due to membrane fouling and, most importantly, high reverse salt fluxes that deteriorate the concentrated product. Polydopamine (PDA) is a widely used, easily applicable, hydrophilic, adhesive antifouling coating. Among the coating parameters, surprisingly, the effect of PDA coating temperature on the membrane properties has not been well studied. Polyethersulfone (PES) 30 kDa ultrafiltration membranes were PDA-coated with varying dopamine concentrations (0.5–3 g/L) and coating temperatures (4–55 °C). The quality of the applied coating has been determined by surface properties, water permeability and reverse salt flux using a 1.2 M MgSO4 draw solution. The coating thickness increased both with the dopamine concentration and coating temperature, the latter having a remarkably stronger effect resulting in a higher PDA deposition speed and smaller PDA aggregates. In dead‑end stirred cell, the membranes coated at 55 °C with 2.0 g/L dopamine showed NaCl and MgSO4 retentions of 41% and 93%, respectively. In crossflow FO, a low reverse MgSO4 flux (0.34 g/m2·h) was found making a very low specific reverse salt flux (Js/Jw) of 0.08 g/L, which outperformed the commercial CTA FO membranes, showing the strong benefit of high temperature PDA-coated PES membranes to assure high quality products.
... FO is a kind of osmotically driven filtration method in which a semi-permeable membrane is required to block the total dissolved solids and at the same time allow the passage of clean water [6]. The principle behind this method is the dilution of highly concentrated draw side and at same time concentrating the feed side with consequent salt rejection by the membrane [7]. The main advantage of this method is that it does not require high energy and electricity like other membrane-based techniques [8,9]. ...
Article
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This study was conducted to develop ultrathin forward osmosis (FO) membrane by phase inversion process. Hydrophilic cellulose acetate (CA) polymer and titanium dioxide (TiO2) nanoparticles were used to form a highly water permeable and stable FO membrane. The physical characteristics of prepared nanomaterial and membrane were characterized by scanning electron microscopy, elemental mapping and x-ray diffraction. The FO performance of the developed membrane was evaluated in terms of pure osmotic water flux and reverse salt flux. A consistent water flux was observed during a long-term experiment with the help of the fabricated membrane. Average water flux of 33.63 L/m²/h and reverse salt flux of 10.34 g/m²/h were achieved due to extensive hydrogen bonding between cellulose ester and titania particles. The resultant membrane was found to be highly efficient in terms of FO performance and can be utilized for efficient desalinization of water.
... While there have been a couple of review papers in recent years concerning the basic principles of FO [21][22][23][24], draw solutions [22,[25][26][27][28][29][30][31], applications [21,25,27,[32][33][34][35][36][37][38][39], (bio)fouling [22,25,26,30,[40][41][42][43][44][45][46], membrane fabrication [19,23,30,35,39,43,47,48], or upscaling [49,50], we, for the major part of this review, discuss the challenges of FO evidences from various literatures to prove the unreliability of the existing structural parameter approaches. In addition, we will highlight that, beyond a certain water permeability, the true bottleneck is the mechanical support of the membrane instead of the selective membrane layer. ...
Article
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The use of forward osmosis (FO) for water purification purposes has gained extensive attention in recent years. In this review, we first discuss the advantages, challenges and various applications of FO, as well as the challenges in selecting the proper draw solution for FO, after which we focus on transport limitations in FO processes. Despite recent advances in membrane development for FO, there is still room for improvement of its selective layer and support. For many applications spiral wound membrane will not suffice. Furthermore, a defect-free selective layer is a prerequisite for FO membranes to ensure low solute passage, while a support with low internal concentration polarization is necessary for a high water flux. Due to challenges affiliated to interfacial polymerization (IP) on non-planar geometries, we discuss alternative approaches to IP to form the selective layer. We also explain that, when provided with a defect-free selective layer with good rejection, the membrane support has a dominant influence on the performance of an FO membrane, which can be estimated by the structural parameter (S). We emphasize the necessity of finding a new method to determine S, but also that predominantly the thickness of the support is the major parameter that needs to be optimized.
... In contrast, the same statistical analysis performed on the specific reverse solute flux between pristine and the membrane with the lowest J s /J w , (PN-0.1), produced a p-value of 0.510 -on membrane selectivity without significantly altering the water flux[60]. Nanostructures incorporating AqpZ were reported previously to help maintaining the rejection of the TFC PA layer[35,37]. ...
Article
An ideal forward osmosis (FO) membrane module for osmotic membrane bioreactor (OMBR) application would have high packing density, low reverse solute flux and low fouling propensity. Recently, an outer-selective hollow fiber forward osmosis (HFFO) membrane has been developed to simultaneously improve packing density and reduce fouling propensity. However, a high reverse solute flux of the HFFO membrane still generates a salinity build-up in the reactor and remains the main challenge of this technology. To tackle this problem, we successfully improved the selectivity of an outer-selective HFFO membrane by incorporating a prior developed formulation based on Pluronic® nanostructures containing water selective proteins into the active layer of the membrane. The assimilation of these nanostructures in the membrane resulted in a significant decrease of the specific reverse solute flux from 0.36 ± 0.01 gL⁻¹ to 0.12 ± 0.02 gL⁻¹ with no significant decrease in water flux. Also, urea was selected as a challenging solute to investigate the selectivity of the developed membranes. In comparison with the pristine membranes, membranes containing nanostructures presented a superior rejection of urea from 87.7 ± 2.0 % to 95.2 ± 0.9 %. The developed membranes are able to be used for future OMBR application tests to prove feasibility of the process. Thus, this study can lead to the development of new membranes suitable for efficient and long-term operation in OMBR configurations. Additionally, the nanostructures investigated here can be used for different thin-film composite membranes as an additive to improve membrane selectivity.
... The fouling of FO membranes is mostly reversible (Hartanto et al., 2016a,b;Hawari et al., 2018;Ma et al., 2013;Zou et al., 2019). However, the industrial application of FO still faces several challenges, among which concentration polarization (CP) is the greatest (Zargar et al., 2020). ...
Article
Forward osmosis (FO) has received significant attention recently. FO has high potentials for integration with other water treatment technologies. However, concentration polarization (CP) remains a significant challenge in FO membrane applications. In particular, internal CP (ICP) reduces the permeability of FO membranes by nearly 80%. The development of FO processes and their applications can greatly benefit from strategies that detect and control CP in standalone and integrated FO systems. This requires consideration of FO membrane structures, materials, configurations, operating conditions, and modification and cleaning strategies. This review provides a state-of-the-art analysis of recent literature on CP detection and control with a specific focus on ICP as a major issue in FO processes. This helps to understand current CP mitigation strategies and their challenges and prospects. The first section reviews the structures of different FO membranes and related CP mechanisms. Research on CP and the impacts of various parameters on its magnitude are then discussed, followed by a review of CP phenomena in hybrid FO processes and applied ICP control strategies. Finally, recommendations for future research in CP detection and control are made. This review serves as a valuable reference for future research on FO processes and may contribute to developing more ICP-resistant FO membranes.
... Since the mutation commonly occurs at the outer layer of the virus which targets the spike protein of the virus [7,170], the new COVID-19 variants can be destroyed by a smart membrane by installing a sensor or protein-responsive detector to detect the spike protein of the virus. Stimuli-responsive materials have been explored in the water treatment field to respond under certain conditions such as electric, light, magnetic field, pH, and temperature-responsive [175,176]. The protein stimuli-responsive smart membrane can overcome the bottlenecks of conventional and existing membrane technologies that function as automatic gates through flexible adjustment of pore sizes and surface properties in response to the variants of the targeted viruses. ...
Article
Consumption of pathogenic contaminated water has claimed the lives of many people. Hence, this scenario has emphasized the urgent need for research methods to avoid, treat and eliminate harmful pathogens in wastewater. Therefore, effective water treatment has become a matter of utmost importance. Membrane technology offers purer, cleaner, and pathogen-free water through the water separation method via a permeable membrane. Advanced membrane technology such as nanocomposite membrane, membrane distillation, membrane bioreactor, and photocatalytic membrane reactor can offer synergistic effects in removing pathogen through the integration of additional functionality and filtration in a single chamber. This paper also comprehensively discussed the application, challenges, and future perspective of the advanced membrane technology as a promising alternative in battling pathogenic microbial contaminants, which will also be beneficial and valuable in managing pandemics in the future as well as protecting human health and the environment. In addition, the potential of membrane technology in battling the ongoing global pandemic of coronavirus disease 2019 (COVID-19) was also discussed briefly.
... Pressure-Assisted FO can also mitigate RSF, using NaCl as DS at the expense of additional energy requirements of the hydraulic pressures. Detailed information about RSF mitigation can be found elsewhere [61]. Alternatively, natural or physical methods (such as system design or modification without employing additional chemicals) need to be investigated to mitigate RSF in the FO process. ...
Article
Water scarcity is one of the major issues that has put economic growth, societal stability, and ecosystem balance unstable. Wastewater reuse has been recognised as a viable method for securing potable water supply. Due to its inherent advantages over pressure-driven and energy-intensive reverse osmosis (RO), forward osmosis (FO) is one of the most researched technologies for wastewater reuse applications. However, the draw solution (DS) regeneration stage is one of the key bottlenecks of the process. Membrane distillation (MD), on the other hand, is an emerging technology that could provide a cost-effective thermally-driven purification process, especially when combined with waste heat or solar thermal. Nevertheless, the MD process also has several drawbacks, such as membrane pore wetting. The MD process can effectively regenerate the FO draw solution and produce high-quality water when integrated with the FO process. Within the hybrid process, the FO membrane removes the contaminants from the feed solution and the MD process is only used to regenerate the DS with no significant membrane wetting. It is, therefore, important to study the integrated FO-MD process to overcome the limitations of individual membrane processes. Integrated FO-MD economics, process design, and modelling of different applications are thoroughly reviewed in this contribution. Future research directions and prospects for scale-up are suggested.
... If the DS regeneration, which is energy-intensive, can be adequately managed, FO can potentially offer lower energy consumption compared to pressure-driven membrane processes such as reverse osmosis (RO), ultrafiltration, and nanofiltration that require significant hydraulic pressures to force water through the membranes. FO is also argued to offer lower fouling propensity (which is more reversible) and can be applied to a wide range of solutes and contaminants [1][2][3][4][5]. Similar to RO membranes, a significant limitation with respect to FO application is the occurrence of concentration polarization (CP). ...
Article
Forward osmosis (FO) and reverse osmosis (RO) membrane processes differ in their driving forces: osmotic pressure versus hydraulic pressure. Concentration polarization (CP) can adversely affect both performance and lifetime in such membrane systems. In order to mitigate against CP, the extent and severity of it need to be predicted more accurately through advanced online monitoring methodologies. Whilst a variety of monitoring techniques have been used to study the CP mechanism, there is still a pressing need to develop and apply non-invasive, in situ techniques able to produce quantitative, spatially resolved measurements of heterogeneous solute concentration in, and adjacent to, the membrane assembly as caused by the CP mechanism. To this end, 23Na magnetic resonance imaging (MRI) is used to image the sodium ion concentration within, and near to, both FO and RO composite membranes for the first time; this is also coupled with 1H MRI mapping of the corresponding water distribution. As such, it is possible to directly image salt accumulation due to CP processes during desalination. This was consistent with literature expectations and serves to confirm the suitability of 23Na MRI as a novel non-invasive technique for CP studies.
... If the DS regeneration, which is energy-intensive, can be adequately managed, FO can potentially offer lower energy consumption compared to pressure-driven membrane processes such as reverse osmosis (RO), ultrafiltration, and nanofiltration that require significant hydraulic pressures to force water through the membranes. FO is also argued to offer lower fouling propensity (which is more reversible) and can be applied to a wide range of solutes and contaminants [1][2][3][4][5]. Similar to RO membranes, a significant limitation with respect to FO application is the occurrence of concentration polarization (CP). ...
Article
Forward osmosis (FO) and reverse osmosis (RO) membrane processes differ in their driving forces: osmotic pressure versus hydraulic pressure. Concentration polarization (CP) can adversely affect both performance and lifetime in such membrane systems. In order to mitigate against CP, the extent and severity of it need to be predicted more accurately through advanced online monitoring methodologies. Whilst a variety of monitoring techniques have been used to study the CP mechanism, there is still a pressing need to develop and apply non-invasive, in situ techniques able to produce quantitative, spatially resolved measurements of heterogeneous solute concentration in, and adjacent to, the membrane assembly as caused by the CP mechanism. To this end, ²³Na magnetic resonance imaging (MRI) is used to image the sodium ion concentration within, and near to, both FO and RO composite membranes for the first time; this is also coupled with ¹H MRI mapping of the corresponding water distribution. As such, it is possible to directly image salt accumulation due to CP processes during desalination. This was consistent with literature expectations and serves to confirm the suitability of ²³Na MRI as a novel non-invasive technique for CP studies.
... However, FO technology has some shortcomings that limit its potential, such as reverse solute diffusion (RSD), internal concentration polarization (ICP), and lower flux compared to pressuredriven membranes (Grylewicz & Mozia, 2020;Rezaei-DashtArzhandi, Sarrafzadeh et al., 2018). Many solutions have been proposed to mitigate the impact of these problems, including operational strategies in the form of low hydraulic pressure (,10 bar), electrolysis, or ultrasound and membrane structure modification (Zou, Qin, & He, 2019). AU:5 The latter method captured the interest of many studies due to its effects on water flux, membrane fouling, and selectivity. ...
Article
Forward osmosis (FO) technology has gained tremendous attention in recent years in desalination and wastewater treatment. Developing a new state of the art forward osmosis membranes is vital for advancing the FO technology to achieve commercialization status in the near future. Polymeric membranes such as cellulose triacetate and thin-film composite (TFC) membranes are the only available commercial membranes. Besides being expensive compared to the reverse osmosis membranes, these membranes exhibit lower water flux, high reverse salt flux, prone to irreversible fouling and have a limited lifetime. The emergence of nanotechnology has enabled researchers to design new membranes with superior performance compared to the commercially available membranes. One promising field is the incorporation of nanomaterials into polymeric membranes to enhance their performance. Researching in this space has resulted in the emergence of a new class of membranes discussed in this chapter. The study covered the synthesis process of flat sheet and hollow fibre membranes modified by incorporation of nanoparticles and discussed stimuli-responsive membranes such as pH-responsive, electric field responsive and salt responsive membranes for water purification. The main challenges associated with the commercialization and future research perspectives are also discussed to identify future research aspects.
... Therefore, reducing RSF is critically important to FO operations, and mitigation tactics such as membrane fabrication/modification and selection of a suitable DS have been discussed in a recent review paper. 16 Besides direct effects, RSF can also lead to unfavorable consequences such as the accumulation of DS in the feed solution (i.e., the solute buildup). Note that solute buildup or DS buildup from RSF is a part of salinity buildup in an FO operation, as the latter also includes the concentrating effect (CE) of other substances in the feed solution caused by membrane rejection (Fig. 1). ...
Article
Forward osmosis (FO) has shown advancement towards recovery of useful water from various waste streams. A major issue that arises is the accumulation of salts due to reverse solute flux (RSF) from a draw solution into a feed solution that can result in several negative effects such as decreased water flux and inhibiting biological activities. This paper aims to provide a concise discussion and analysis of methods that can help to alleviate the effects of solute build up. New parameters, solute removal/recovery rate (SRR) and removal/recovery ratio (ReR), are proposed to help better define the performance of reducing solute buildup and employed in case studies to evaluate the selected reduction methods. Solute removal can be accomplished by physical separation, chemical precipitation, and biological removal. Recovery of solutes, one step beyond removal, is discussed and demonstrated by using bioelectrochemical systems and electrodialysis as examples. This work has highlighted the concerns associated with solute buildup and encouraged further exploration of effective tools to mitigate solute buildup for improved performance of FO-based water/wastewater systems.
Article
A series of cellulose triacetate/Ludox‐silica nancomposite pervaporation membranes was successfully prepared via solution casting, aiming to improve the performance of cellulose triacetate membranes for desalination. The fabricated nanocomposite membranes were characterized to study the membrane morphology, chemical composition, mechanical properties, and surface hydrophilicity. Furthermore, the desalination performance was investigated as a function of silica (SiO2) loading (ranging from 1 to 4 wt%) and feed concentration at 30 and 60 g/L of sodium chloride (NaCl). Pervaporation experiments showed that incorporating 4 wt% SiO2 into a cellulose triacetate (CTA) membrane increased the water flux by a factor 2.5 compared with pristine CTA (from 2.2 to 6.1 kg m⁻² h⁻¹) for a 30 g/L NaCl feed solution at 70°C, while the salt rejection remained above 99%. The CTA/4 wt% SiO2 membrane was found to have only 21% flux reduction when tested with a 60 g/L NaCl feed solution, without changes in membrane selectivity. This suggests that the developed CTA/Ludox‐SiO2 nanocomposite pervaporation membrane is suitable for desalination.
Article
The forward osmotic membrane bioreactor (FOMBR) is an emerging innovative technology with broad application prospects in the field of wastewater treatment. Its application is severely limited by concentration polarization, salinity accumulation, and evident water flux decline. Gradual salinity accumulation to a maximum conductivity of 19.7 mS cm⁻¹ under continuous flow operation suppressed the activities of sludge and biodegradation efficiencies. The employment of the regulation of intermittent supernatant discharge was first investigated to alleviate inhibition caused via accumulated salinity in the bioreactor, and bilateral influent was examined with respect to the performance of the FOMBR. The preferable condition to be applied was FO orientation mode (i.e., active layer facing feed) with spacers added to the surface. Given the decreased salt concentration with 2 liters of the supernatant removed per day, the water flux declined more slowly and sludge activities were recovered. When compared to the performance without discharging supernatant, the strategy of controlling salinity could improve the removal efficiencies of NH4⁺-N, PO43–P, and total organic carbon (TOC) by 15.1, 14.3, and 2.3%, respectively. Additionally, the sludge in the intermittent supernatant discharge bioreactor exhibited better sludge property, larger sludge particle size, and recovered sludge activities with the mixed liquid suspended solids (MLSS) stable at around 4.90 g L⁻¹. Therefore, regulation of intermittent salt discharge and controlling the salinity concentration in bioreactor can be employed as an effective method to deal with concentration polarization and salinity accumulation in the FOMBR.
Article
A highly-efficient, autonomous electrochemical-osmotic system (EOS) is developed for simultaneous recovery of electric energy, water, and metals from wastewater. We demonstrate that the system can generate a maximum electric power density of 10.5 W m2 by a spontaneous Fe/Cu2+ galvanic cell, while simultaneously achieving copper recovery from wastewater. With an osmotic pressure difference generated by the deployed electrochemical reactions, water is osmotically extracted from the feed solution by the EOS at a water flux of 5.1 L m2 h1. A scaled-up EOS realizes a power density of 105.8 W per m3 of treated water to light an LED over 24 hours, while also enhancing water extraction and metal recovery. The modularized EOS obtains ultra-high (>97.5%) Faradaic efficiencies at variable operating conditions, showing excellent system stability. EOS is also versatile: it can recover Au, Ag, and Hg from wastewaters with simultaneous electricity and water co-production. Our study demonstrates a promising pathway for realizing multi-resource recycling from wastewater by coupling electrochemical and osmotic-driven processes.
Article
Forward osmosis (FO) has great potential for low energy consumption wastewater reuse provided there is no requirement for draw solutes (DS) regeneration. Reverse solute flux (RSF) can lead to DS build-up in the feed solution. This remains a key challenge because it can cause significant water flux reduction and lead to additional water quality problems. Herein, an osmotic photobioreactor (OsPBR) system was developed to employ fast-growing microalgae to consume the RSF nutrients. Diammonium phosphate (DAP) was used as a fertilizer DS, and algal biomass was a byproduct. The addition of microalgae into the OsPBR proved to maintain water flux while reducing the concentrations of NH4⁺-N, PO4³⁻-P and chemical oxygen demand (COD) in the OsPBR feed solution by 44.4%, 85.6%, and 77.5%. Due to the forward cation flux and precipitation, intermittent supplements of K⁺, Mg²⁺, Ca²⁺, and SO4²⁻ salts further stimulated algal growth and culture densities by 58.7%. With an optimal hydraulic retention time (HRT) of 3.33 d, the OsPBR overcame NH4⁺-N overloading and stabilized key nutrients NH4⁺-N at ∼ 2.0 mg L⁻¹, PO4³⁻-P < 0.6 mg L⁻¹, and COD < 30 mg L⁻¹. A moderate nitrogen reduction stress resulted in a high carbohydrate content (51.3 ± 0.1%) among microalgal cells. A solids retention time (SRT) of 17.82 d was found to increase high-density microalgae by 3-fold with a high yield of both lipids (9.07 g m⁻³ d⁻¹) and carbohydrates (16.66 g m⁻³ d⁻¹). This study encourages further exploration of the OsPBR technology for simultaneous recovery of high-quality water and production of algal biomass for value-added products.
Article
The rejection of disinfection byproducts (DBPs) is an important consideration for the application of forward osmosis (FO) in wastewater recycling. However, the transport of organic compounds in FO is not well predicted by existing models, partially because these models have not incorporated the effect of reverse salt flux, a phenomenon previously shown to influence the transport of pharmaceutical compounds. In this study, we investigated the effects of reverse salt flux on DBP transport in FO and the corresponding mechanisms. We used a commercial Aquaporin membrane and tested sixteen DBPs relevant to wastewater recycling. Using draw solutions constituted by NaCl, MgSO4, or glucose in a bench-scale FO system, we first confirmed that higher reverse salt flux resulted in lower DBP permeance. By integrating results from the bench-scale FO system and those from diffusion cell tests, we showed that two mechanisms contributed to the hindered DBP transport: the steric hindrance in the active layer caused by the presence of the draw solute and the retarded diffusion of DBPs in the support layer via a “salting-out” effect. Lastly, we developed a modified solution-diffusion model incorporating these two mechanisms by accounting for the free volume occupied by draw solute molecules in the active layer and by introducing the Setschenow constant, respectively. The modified model significantly improved the prediction of permeance for halogenated DBPs, and revealed the relative importance of steric hindrance (dominant for large DBPs) and retarded diffusion (dominant for hydrophobic DBPs). The modified model did not accurately predict the permeance of nitrosamines, attributable to their extremely high hydrophilicity or large size.
Article
Recently, thermo-responsive nonionic amphiphilic copolymers have shown great potential as forward osmosis (FO) draw solute for high-salinity water desalination and zero-liquid discharge (ZLD). However, the relationship between the copolymer structural properties and key characteristics as draw solutes, as well as copolymer's chemical stability after regeneration have not been much studied. In this work, we systematically investigated poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide) (PEO-PPO-PEO) copolymers as draw solute. The results showed that the PEO segments significantly influenced the viscosity, osmotic pressure and lowest phase separation temperature of the copolymer aqueous solutions. Among four commercial copolymers studied, Pluronic® L35 with moderate molecular weight (Mn 1,900 Da), 50% PEO, and relatively high hydrophilic-lipophilic balance (HLB) showed the best draw solution (DS) performance. It also showed great stability in physiochemical properties and draw capacity after more than ten cycles of regeneration. On the other hand, despite the fact that membrane fouling was observed due to the use of copolymer DS, the FO flux (∼1.2 L m‒2 h‒1, as similar with the virgin membrane) was not affected when high-salinity feedwater such as seawater RO brine was applied. Overall, our study has provided a more comprehensive understanding on the characteristics of nonionic amphiphilic copolymer DS and showcased the promise of copolymer-driven FO process in high-salinity water desalination and ZLD.
Article
A suitable draw solute (DS) concentration in bioelectrochemically assisted osmotic membrane bioreactor (BEA-OMBR) can convert the “negative effect” of salinity accumulation into a “beneficial effect” by using the reverse-fluxed DS as a buffer agent or a carbon source supplement. Herein, the effect of DS concentration from acid buffer solution (i.e., ammonium chloride, NH4Cl), alkaline buffer solution (i.e., sodium bicarbonate, NaHCO3), and organic solution (i.e., sodium acetate, NaOAc) on salinity accumulation was systematically investigated. Salinity accumulation with NaHCO3 DS mainly derived from reversal fluxed sodium ion (Na⁺, major contributor with DS concentration ≤0.25 M) and bicarbonate ion (main contributor with DS concentration ≥0.50 M): Na⁺ accumulation could be mitigated by Na⁺ transport dominant by electrically driven migration (i.e., 21.3∼62.1% of reverse-fluxed Na⁺), and bicarbonate accumulation could be reduced by buffer system. A medium-low concentration of 0.25 M NH4Cl DS had a better performance on current density of 165.0±23.0 A m⁻³ and COD removal efficiency of 91.5±3.4 % by taking advantage that 77.7±1.3% of reverse-fluxed ammonium could be removed by biological treatment and ammonium transport. A high NaOAc DS concentration (i.e., ≥0.05 M) exhibited a higher current density of 145.3∼146.0 A m⁻³ but a lower COD removal efficiency due to the limited carbon source utilization capacity of anaerobic bacteria. Both concentration diffusion (20.9∼28.3%) and electrically driven migration (29.5∼39.4%) promote reverse-fluxed Na⁺ transport to catholyte and thus mitigated Na⁺ accumulation in the feed/anolyte. These findings have provided an optimal DS concentration for BEA-OMBR operation and thus encourage its further development.
Article
This study investigated the chemical stability of various forward osmosis (FO) after static exposure to multi-effect distillation (MED) brine. The water flux, forward salt flux (FSF), and specific reverse salt flux (SRSF) were evaluated to evaluate the membrane performance degradation. The changes in the physicochemical properties of FO membranes were elucidated via characterization techniques including Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), goniometer, and zeta potential analyzer. Moreover, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach was used to predict the changes in the membrane fouling propensity. The results showed that the cellulose triacetate (CTA) membrane suffered deacetylation and chain cleavage due to hydrolysis, whereas the thin-film composite (TFC) membrane experienced degrafting due to oxidation. The selectivity reductions of both membranes were observed according to the increase in FSF and SRSF. Furthermore, the decreasing attractive XDLVO interaction energies of the degraded CTA membrane indicated the improvement of anti-fouling properties. In contrast, the anti-fouling properties of the TFC membrane were severely reduced since the attractive XDLVO interaction energies increased.
Article
Reverse solute flux (RSF) is a key issue for operating forward osmosis (FO) systems and can cause the loss of draw solute (DS) and salt accumulation in the feed. Herein, an electrolysis-assisted FO (e-FO) system was developed for simultaneous RSF reduction and recovery of the reverse-fluxed DS. Applying a voltage of 1.5 V led to RSF of 3.34 ± 0.01 mmol m⁻² h⁻¹ (0.47 g m⁻² h⁻¹) in the e-FO system, 67.5 ± 0.5% lower than that of the control system; in addition, the e-FO system recovered ~0.32 g L⁻¹ of the reverse-fluxed DS and this could not be realized in the control. When the e-FO system was examined with three types of the mimicked fertilizer, RSF reduction and DS recovery were largely affected by the individual components of a fertilizer DS. The energy consumption of the e-FO system was reduced by ~90%, from 0.38 ± 0.01 to 0.04 ± 0.01 kWh m⁻³ when the recirculation rate decreased from 60 to 15 mL min⁻¹. Those results have demonstrated the technical feasibility of an e-FO system that is capable of reducing RSF and recovering the lost DS and will encourage further investigation by addressing several identified challenges.
Article
Responsive hydrogels have long been researched for their ability to change their conformation and properties when stimulated at different conditions. Their ability to imbibe and expel substantial amount of water without rupturing its structure led to their prominent usage in wastewater treatment. Recently, increasing studies were focus on coupling hydrogels with non-pressure driven membrane technology such as membrane distillation (MD) or forward osmosis (FO) for wastewater treatment. Membrane fouling or reduced water flux had always been a major challenge in MD processes that hindered its full efficiency in recovering purified water. Hydrogel was found to be able to improve water flux by increasing hydrophilicity of the membrane that enables the repulsion of foulants that interact with the membrane via hydrophobic interactions. As with the case of MD, FO process also faced membrane fouling besides requiring energy and cost-intensive secondary processes to recover draw solutions. Hence, using stimuli responsive hydrogels as draw solutions to reduce the energy requirement in draw solution recovery has been extensively studied. This review aims to discuss various types of stimuli responsive hydrogels in mitigating problems faced by MD and FO and its associated problems such as flux hindering, wetting and limiting osmotic pressure. The research gap was identified and further research that require attention such as flux enhancement, fouling mitigation as well as gel layer resistance problems were outlined. Concerted efforts were also reported on the state-of-art multi-responsive hydrogel copolymerized with more hydrophilic functional groups or electrolytes to solve the above-mentioned problems.
Article
Forward osmosis (FO) membrane fouling is a big obstacle in real textile wastewater treatment. Herein, a series of pretreatments include coagulation (C), microbubbles (Mbs) and their combination process (Mbs + C) were used to alleviate membrane fouling. Their different effects on flux and rejection rate of FO membrane were also investigated. Satisfactory removal efficiencies for UV254, dissolved organic carbon (DOC), chemical oxygen demand (COD) and antimony (Sb) of 48.27, 47.80, 40.70 and 41.87% were obtained at the optimum polyaluminum chloride (PAC) dosage of 300 mg L⁻¹ and combined treatment time of 15 min. Compared with C alone, combined Mbs + C resulted in smaller flux decrease (~40%) and higher rejection rate (>98%) of FO membrane. This result confirmed the positive effect of Mbs on the combined processes. Fluorescence excitation-emission matrices coupled with parallel factor (EEM-PARAFAC), gel permeation chromatography (GPC) and gas chromatography mass spectrometry (GC–MS) measurements were further carried out to investigate the mitigation effect of pretreatments on membrane fouling. Results exhibited Mbs + C can significantly remove tryptophan-like substance and aliphatic alcohols due to enhanced coagulation-floatation property and oxidation of hydroxyl radicals. This study provides useful insights for fouling mitigation through Mbs and coagulation in actual FO process when dealing with textile wastewater.
Article
Recent years, the separation of organic liquid mixtures achieved by organic solvent nanofiltration (OSN), organic solvent reverse osmosis (OSRO), and organic solvent forward osmosis (OSFO) has gained a great momentum. In the methods, it is of particular importance to know the osmotic pressure of liquid mixtures for the correct process design. Although the Van’t Hoff law is frequently employed to estimate the osmotic pressure of such mixtures, unprecedented serious errors might be added to the results. In this study, the osmotic pressure of numerous liquid mixtures is predicted using the original definition of osmotic pressure along with the cubic plus association (CPA) equation of state (EoS) and the Van’t Hoff equation at various temperatures and compositions. CPA EoS considers hydrogen bonding effects in associating compounds (those with hydrogen bonds such as water and alcohols). The obtained results reveal that unlike the Van’t Hoff equation (the average deviation = 19.95 bar), the original definition of osmotic pressure with the aid of CPA EoS (the average deviation = 3.86 bar) can properly predict the osmotic pressure of the studied mixtures. Our findings are beneficial for various techniques utilized in the separation of organic liquid mixtures.
Article
Forward osmosis (FO) has attracted research attention as the energy-effective water separation process. For a FO process, it is important to prevent leakage of a solute of the DS. As a low-leakage solute, a branched thermo-responsive oligomer, pentaerythritol-oligo(ethylene oxide)m-b-(butylene oxide)n oligomers (PEBs), had been reported. In this study, the relationship between the chemical structure and the permeability of the PEBs through a FO membrane had been investigated in detail. For the detailed investigation, the mole fraction of each component having different absolute molecular weights in the PEBs was determined by the MALDI/TOF-MS, then the permeabilities of the components through the FO membrane were independently quantified. As the result, for the PEBs with low absolute molecular weight, the permeability of the PEBs was strongly affected by the molecular weight of the PEBs. On the other hand, for the PEBs with high absolute molecular weight, it was confirmed that the permeability of the PEBs was affected by the hydrophobicity of the PEBs. Conclusively, it was indicated that not only the molecular weight but also the affinity between the PEBs and the FO membrane is important for the reverse solute flux.
Article
Development of stable membranes with high permeability and high separation performance are highly desirable but challenging for polyamide-based forward osmosis (FO) membrane. Herein, a novel FO membrane is prepared through the formation of polyamide (PA) selective layer on Cu-alginate hydrogel intermediate layer-modified polyethersulfone (PES) support. The formed dense, uniform, and crumbled PA selective layer is firmly “hooked” on the Cu-alginate intermediate due to the strong chelation crosslinking between the Cu²⁺ in the intermediate layer and –NH2 groups of MPD. Meanwhile, the hydrophilic tri-functional Cu-Alginate intermediate layer promotes the enhancement of the water flux and acted as an effective barrier for high heavy metal ions (Cd²⁺, Cu²⁺, Pb²⁺) rejection (>96%) owing to the additional charge repulsion effect by the Cu²⁺ in the membrane matrix. The water flux of the resultant composite FO membrane (PES/Cu-SA/PA) was doubled that of the membrane without modification. Moreover, the membrane exhibited a steady water flux decline during a continuous 24 h sludge thickening process, as compared with the 10 h fast decline of the water flux of with the pristine FO membrane. This work underscores the progress of intermediate layer-assisted formation of the polyamide films as a promising strategy for the design of FO membranes with good stability for efficient removal of heavy metal ions as well as extended applications like sludge thickening.
Article
Regeneration and reuse of draw solute (DS) is a key challenge in the application of forward osmosis (FO) technology. Herein, EDTA-Na2 was studied as a recoverable DS for water extraction by taking advantages of its pH-responsive property. The FO system using EDTA DS achieved a higher water flux of 2.22 ± 0.06 L m⁻² h⁻¹ and a significantly lower reverse salt flux (RSF) of 0.06 ± 0.01 g m⁻² h⁻¹, compared to that with NaCl DS having either the same DS concentration or the same Na⁺ concentration. The suitable pH range for the application of EDTA DS was between 4.0 and 10.5. A simple recovery method via combined pH adjustment and microfiltration was employed to recover EDTA DS and could achieve the recovery efficiency (at pH 2) of 96.26 ± 0.48%, 97.13 ± 1.03% and 98.56 ± 1.40% by using H2SO4, H3PO4 and HCl, respectively. The lowest acid cost for DS recovery was estimated from 0.0012 ± 0.0001 to 0.0162 ± 0.0003 $ g⁻¹ by using H2SO4. The recovered EDTA DS could be reused in the subsequent FO operation and the overall recovery efficiency was 94.4% for four reuse cycles. These results have demonstrated the feasible of EDTA-Na2 DS and a potentially cost-effective recovery approach, and encouraged further exploration of using EDTA-based compounds as a draw solute for FO applications.
Article
The forward osmosis (FO) process was suggested as a pretreatment to a multi-stage flashing (MSF) plant to reduce the environmental impact of brine discharge and the chemicals used. Yet, there is no study investigating the performance of the FO process pretreatment to the MSF plant using tertiary sewage effluent (TSE) as a feed solution. Combining MSF brine with the TSE generates a considerable permeation flux, reducing the membrane area and capital cost. This study evaluated the performance of the FO process for indirect desalination of the MSF brine, considering membrane fouling, cleaning, required membrane area and the specific power consumption. The FO process used a thin-film composite (TFC) membrane to dilute the brine reject from the MSF plant by the TSE and hence converting waste solutions into a feasible water resource. A considerable high water flux (±35 L/m2h) was generated and slightly decreased throughout each experiment's 4 cycles. An enhancement in the water permeability was observed in the FO tests with a prefiltration of the brine reject and the wastewater with 20 μm and an osmotic backwash cleaning of the used membrane. The prefiltration of the draw and feed solutions was effective in minimizing the impact of fouling. Maximum power consumption of 0.007 kWh/m³ was consumed in the forward osmosis process without prefiltration and decreased to 0.006 kWh/m³ in the FO process. The proposed FO system successfully diluted the brine reject’ divalent ions, reducing their concentration to 43% in some cases. Depending on the FO membrane orientation, the TSE feed solution resulted in a 276%–473% reduction in the number of FO elements required in the FO process compared to the seawater feed solution.
Article
Forward osmosis is an emerging osmosis-driven membrane process, which has benefits of low energy consumption, low operational pressure, easy equipment, and low fouling. This review paper summarized the recent advances of forward osmosis technology based on the publications collected from Science Direct since 1996. Through the statistical analysis of 9345 articles, it was concluded that the research of forward osmosis mainly focused on the draw solution, membrane development, membrane fouling, and energy consumption. In this review, the most significant influencing factors of forward osmosis technology were analyzed, including membrane development, draw solution, and the operating conditions; then the existing problems were discussed in detail, including concentration polarization, membrane fouling, and reverse solute diffusion, which are closely related to each other; finally, the innovations and bottlenecks of forward osmosis technology were summarized, and the future perspectives were discussed. More attention should be paid to developing new membrane materials, designing effective draw solutions, minimizing the energy consumption, and creating energy-efficient recovery processes, to expand its commercial application. This review will deepen the understanding to forward osmosis technology, and provide comprehensive information for the scientific researcher and application engineers to facilitate the research and development of forward osmosis technology.
Article
The water content in the recycled alginate solutions from aerobic granular sludge was nearly 100%. Forward osmosis (FO) has become an innovative dewatering technology. In this study, the FO concentration of sodium alginate (SA) was investigated using calcium chloride as a draw solute. The reverse solute flux (RSF) of calcium ions in FO had a beneficial effect, contrary to the findings of previous literature. The properties of the concentrated substances formed on the FO membrane on the feed side were analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, verifying that calcium alginate (Ca-Alg), which can be used as a recycled material, was formed on the FO membrane on the feed side owing to the interaction between SA and permeable calcium ions. Water flux increased significantly with the increase in calcium chloride concentration, while the concentration of SA had little influence on the water flux in FO. Based on this discovery, we propose a novel method for the concentration and recovery of alginate, in which the RSF of calcium ions is utilized for recovering Ca-Alg by FO, with calcium chloride as a draw solute.
Article
Ion exchange membranes (IEMs) are undergoing prosperous development in recent years. More than 30000 papers which are indexed by Science Citation Index Expanded (SCIE) have been published on IEMs during the past twenty years (2001-2020). Especially, more than 3000 papers are published in the year of 2020, revealing researchers’ great interest in this area. This paper firstly reviews the different types (e.g., cation exchange membrane, anion exchange membrane, proton exchange membrane, bipolar membrane) and electrochemical properties (e.g., permselectivity, electrical resistance/ionic conductivity) of IEMs and the corresponding working principles, followed by membrane synthesis methods, including the common solution casting method. Especially, as a promising future direction, green synthesis is critically discussed. IEMs are extensively applied in various applications, which can be generalized into two big categories, where the water-based category mainly includes electrodialysis, diffusion dialysis and membrane capacitive deionization, while the energy-based category mainly includes reverse electrodialysis, fuel cells, redox flow battery and electrolysis for hydrogen production. These applications are comprehensively discussed in this paper. This review may open new possibilities for the future development of IEMs.
Article
Synergistic fouling effects between proteins and polysaccharides in forward osmosis (FO) and the related thermodynamic mechanisms were studied at the molecular level. Two noteworthy fouling phenomena were found after filtering same amount of foulants: 1) the flux reduction of bovine serum albumin (BSA)‑sodium alginate (SA) combined foulants (67.2%) was much higher than that of individual foulants (14.8% for BSA and 31.8% for SA); 2) the flux reduction of combined foulants showed a “logarithmic” trend, while that of individual foulants showed a “linear” trend. Density functional theory calculation and experimental characterization revealed that the electrostatic association between BSA and SA induced the formation of stable gel network. Based on Flory-Huggins theory, the high chemical potential gap caused by this gel network is responsible for the significant flux reduction of combined foulants in initial fouling stage. However, the reverse NaCl diffusion non-linearly reduced the electrostatic repulsion between BSA-SA chains, triggering the dynamic transition of combined foulants from gel to flocs. As a result, newly adhered foulants formed a cake layer, causing only a slight flux loss in later fouling stage. This study clearly revealed the crucial role of reverse solute diffusion in dynamically governing the synergistic fouling effects between proteins and polysaccharides.
Article
The discharge of reject brine from seawater desalination processes is a threat to marine ecosystems. This study investigated the feasibility of forward osmosis (FO) for the treatment of reject brine from multi‐effect distillation (MED) systems. The performances of two commercial FO membranes (ie, cellulose triacetate (CTA) and polyamide thin film composite (TFC) membranes) were compared. The effects of operating conditions, such as draw solution concentration, cross‐flow velocity, and temperature, on concentration polarization and consequently on the water flux, were quantitatively analyzed using a mathematical model. Results showed that the batch FO process could effectively reduce the volume of MED brine to 54.9% using 3 mol/L NaCl. As the draw solution concentration increased from 1 mol/L‐5 mol/L, a significant increase in the initial water flux from 3.23 L·m⁻²·h⁻¹‐17.88 L·m⁻²·h⁻¹ and from 3.55 L·m⁻²·h⁻¹‐24.04 L·m⁻²·h⁻¹ was observed for the CTA and TFC membranes, respectively. However, the proportions of the effective osmotic pressure differences decreased from 20.7% to 11.9% and from 23.5% to 6.2% for the CTA and TFC membranes, respectively, indicating the concentration polarization (CP) was severe for high‐salinity brine treatment. The positive effects of increasing cross‐flow velocity on CP were limited. Moreover, the high temperature of the MED brine effectively mitigated the internal concentration polarization (ICP), thereby enhancing the water flux. Overall, this study provides valuable guidance for the application and optimization of FO in MED brine treatment. This article is protected by copyright. All rights reserved.
Article
This work discusses the preparation, characterization, and feasibility test of composite zeolite hollow fiber membranes, with UV-curable resin as a secondary coating material, in removing Ni (II) using FO process. The preparation of the membrane started by depositing zeolite membrane onto alumina hollow fiber, followed by photopolymerization process once the outer layer was fully covered. Various characterization techniques were used on the composite membrane, namely field emission-scanning electron microscopy (FESEM), X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) analysis, contact angle measurement, and performance tests using FO. The results show that the membranes enabled a reduction of reverse solute once incorporated with UV-curable resin. The lowest reverse solute flux obtained was 0.008 kg m⁻² h⁻¹, when pure water was flowed in the outer surface and 100,000 mg L⁻¹ sodium chloride (NaCl) was used in the lumen. The UV-curable resin was unstable in the presence of Ni (II), which later formed complex ions. Adsorption of Ni (II) ions caused agglomeration of zeolite particles, causing membrane defects.
Article
Socioeconomic development and new technological advancements have greatly increased the demand for metals, minerals and nutrients. Thus, substantial interest in developing technologies to recover these commodities from seawater, various brines and wastewater streams (industrial and domestic) has emerged. Less explored and innovative membrane processes including membrane crystallization (MCr), forward osmosis (FO) and membrane capacitive deionization (MCDI) are gaining interest in this regard. The current study provides a critical review of the current trends in applying MCr, FO and MCDI for recovery of metals, minerals and nutrients from various streams. The processes are compared in terms of types of fouling, energy consumption, overall composition of suitable feed solutions, feasible concentration ranges and potential to recover the targeted metal from a multi-component solution. The ultimate objective is to establish future research directions for further improvement of each process and to identify which of the processes is more suitable under a given scenario.
Article
Salinity accumulation in osmotic membrane bioreactors (OMBRs) is one of the key challenges, which can be mitigated in situ by reverse-fluxed solute transport through integration of bioelectrochemical systems (BES). The effects of several key operating parameters on salinity accumulation were investigated. Salinity accumulation depended on balance between reversal solute flux (RSF) and reverse-fluxed ammonium (RFA) transport, which was driven by electrical migration and concentration diffusion. DS concentration was the primary factor influencing RSF, and the lowest DS concentration exhibited the minimum solute leakage. Aeration played a vital role in RFA transport, and a higher aeration helped to enhance RFA transport. Increased current generation (i.e., influent flow rate of 0.5 mL min-1 and external resistance of 5.0 Ω) contributed to RFA migration. The lack of electrolyte addition in catholyte contributed to RFA diffusion. These optimal parameters encourage the further development of an effective strategy for salinity mitigation in BES-based OMBR technology.
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Forward osmosis (FO) has recently emerged as a new separation platform for a range of applications that are currently not possible for other membrane processes. This review paper covers key aspects of FO development with a specific emphasis on current technical challenges for practical applications. Main hurdles in the transition of FO from a lab-scale process to large scale applications include low-performance membranes, development of suitable draw solute, inherent transport phenomena (e.g. concentration polarization and reverse solute flux), membrane fouling and subsequent membrane cleaning. Several new FO membranes have been developed with some improved performances but no membrane has yet been found convincing in all of the key performance indicators. Draw solutes have been broadly investigated but mainly at the lab-scale. There have only been very few pilot-scale studies, most of them using inorganic salts as draw solutes. Development of thermo-responsive draw solutes and TFC membranes have been reported to be most effective in reducing reverse solute flux while altering the hydrodynamic conditions and the use of ultrasonication along with exploring other viable options have been suggested to tackle external and internal concentration polarization respectively. Although membrane fouling types and mitigation strategies have been extensively explored, this review also highlights the need for further research in biofouling for long-term FO operation.
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Water scarcity, expected to become more widespread in the coming years, demands renewed attention to freshwater protection and management. Critical to this effort is the minimization of freshwater withdrawals and elimination of wastewater discharge, both which can be achieved via zero liquid discharge (ZLD), an aggressive wastewater management approach. Because of the high energetic cost of thermal desalination, ZLD is particularly challenging for high-salinity wastewaters. In this review, we discuss the potential of high pressure reverse osmosis (HPRO) (i.e., reverse osmosis operated at hydraulic pressure greater than ~100 bar) to efficiently desalinate hypersaline brines. We first discuss the inherent energy-efficiency of membrane processes as compared to conventional thermal processes for brine desalination. We then highlight the opportunity of HPRO to reduce energy requirements for desalination of key high-salinity industrial wastewaters. The current state of membrane materials and processes for hypersaline brine desalination is also discussed, emphasizing several process-design considerations unique to HPRO. Lastly, we discuss the most pressing research needs for the development of HPRO, notably the development of membranes and modules suitable for high pressures as well as fundamental studies of compaction and transport at HPRO conditions.
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Endocrine disrupting compounds (EDCs), an important class of micropollutants with potent adverse health effects, are generally poorly rejected by traditional thin film composite polyamide membranes and thus pose significant risks in membrane-based water reclamation. We hypothesize that membrane rejection of hydrophobic EDCs can be enhanced by a hydrophilic surface coating. Using polydoamine (PDA) as a model hydrophilic coating layer, the PDA-coated NF90 membrane experienced up to 75% reduction in the passage of bisphenol A compared to the control (NF90 without coating). Meanwhile, we also observed systematic increase in the rejection of three hydrophobic parabens upon increased PDA coating time. In contrast, there were no systematic changes in the rejection of neutral hydrophilic polyethylene glycol, which suggests that the enhanced EDCs rejection was due to weakened EDCs-membrane hydrophobic interaction. Further sorption tests revealed that the hydrophilic PDA coating could effectively decrease EDCs sorption by the membrane, which is responsible for the improved rejection as predicted by the solution-diffusion theory. The current study reveals an exciting opportunity of engineering membrane surface properties to enhance the rejection of targeted micropollutants, which has important implications in membrane-based water reclamation.
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Desalination membranes are essential for the treatment of unconventional water sources, such as seawater and wastewater, to alleviate water scarcity. Promising research efforts on novel membrane materials may yield significant performance gains over state-of-the-art thin-film composite (TFC) membranes, which are constrained by the permeability–selectivity tradeoff. However, little guidance currently exists on the practical impact of such performance gains, namely enhanced water permeability or enhanced water–solute selectivity. In this critical review, we first discuss the water permeabilities and water–solute selectivities of current TFC membranes and the effect that these active-layer properties have on the performance of desalination processes. We then highlight and provide context for recent module-scale modeling studies that have found limited impact of increased water permeability on the efficiency of desalination processes. Next we cover several important examples of water-treatment processes where inadequate membrane selectivity hinders process efficacy due to permeation of undesired feed solutes and process efficiency due to the need for additional process steps. We conclude with a brief discussion of how the need for enhanced selectivity may influence the design strategies of future membranes.
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The enormous potential of harvesting energy from salinity gradients has been discussed for decades, and pressure-retarded osmosis (PRO) is being increasingly investigated as a method to extract this energy. Despite advancements in membranes and system components, questions still remain regarding the overall viability of the PRO process. Here, we review PRO focusing on the net energy extractable and the ultimate feasibility of the most widely explored configurations. We define the maximum energy that can be obtained from the process, quantify losses and energetic costs that will reduce the net extractable energy, and explain how membrane modules can be improved. We then explore the potential of three configurations of PRO: systems designed to control mixing where rivers meet the sea, power plants that utilize the high concentration gradients available from hypersaline solutions, and PRO systems incorporated into reverse osmosis desalination plants to reduce electricity requirements. We conclude by considering the overall outlook of the process and identifying the most pressing challenges for future research.
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Forward osmosis (FO), as an emerging technology for seawater desalination and wastewater reuse, has been attracting significant interest because of its energy efficiency. However, membrane fouling represents one of the major limitations for this technology, notably for thin film composite (TFC) polyamide (PA) membranes, which are prone to chlorine attack. In this study, silver nanoparticle (AgNPs)-decorated graphene oxide (GO) nanosheets (as an effective biocidal material) were covalently bonded to the PA surface to impart improved hydrophilicity and antibacterial properties to the membrane. AgNPs were synthesized in situ by the wet chemical reduction of silver nitrate onto the surface of GO nanosheets. The formation of the composite was verified by UV-vis spectroscopy, X-ray diffraction, and transmission electron microscopy techniques. The synthesized GO/Ag nanocomposites were then covalently bonded onto the TFC PA membrane surface using cysteamine through an amide forming condensation reaction. ATR-FTIR and XPS results confirmed the covalent bonding of the nanocomposite onto the TFC PA surface. Overall, the GO/Ag nanocomposite functionalized membranes exhibited super-hydrophilic properties (contact angles below 25°) and significant bacterial (E. coli) inactivation (over 95% in static bacterial inactivation tests) without adversely affecting the membrane transport properties.
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Forward osmosis (FO) is one of the evolving membrane technologies in desalination with recent expanded new interest as a low energy process. The most significant parts of FO process are the membrane and draw solution since both play a substantial role in its performance. Hence, the selection of an appropriate membrane and draw solution is crucial for the process efficiency. Improvements in the development of membranes and draw solutes have been recorded recently. However, limitations such as fouling of FO membranes, reverse solute flux, concentration polarization, and low permeate flux in standalone FO systems. This work targets the review of recent progress in FO, aiming on the prospects and challenges. It starts with addressing the advantages of the FO process. The crucial part of this review is a thorough discussion of hybrid FO systems, different FO membranes, and draw solutes available coupled with their effects on FO performance. Finally, the future of FO for sustainable desalination is also discussed.
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Poly (aspartic acid sodium salt) (PAspNa) was evaluated for its potential as a novel draw solute in forward osmosis (FO). The inherent advantages of PAspNa, such as good water solubility, high osmotic pressure, and nontoxicity, were first examined through a series of physicochemical analyses and atomic-scale molecular dynamics simulations. Then, lab-scale FO tests were performed to evaluate its suitability in practical processes. Compared to other conventional inorganic solutes, PAspNa showed comparable water flux but significantly lower reverse solute flux, demonstrating its suitability as a draw solute. Moreover, fouling experiments using synthetic wastewater as a feed solution demonstrated that PAspNa reversely flowed to the feed side reduced inorganic scaling on the membrane active layer. The recyclability of PAspNa was studied using both nanofiltration (NF) and membrane distillation (MD) processes, and the results exhibited its ease of recovery. This research reported the feasibility and applicability of FO-NF or FO-MD processes using PAspNa for wastewater reclamation and brackish water desalination. Copyright © 2015 Elsevier Ltd. All rights reserved.
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The reverse salt flux phenomenon of forward osmosis affects the quality of the feed water, reduces water flux, and increases the cost for replenishing lost draw solute. In this study, a novel draw solution comprising a mixture of Triton X100 and Na3PO4 for minimizing the reverse salt flux during forward osmosis (FO) was explored. The results indicated that the reverse salt flux caused by coupling 0.5 mM Triton X100 to 0.55 M Na3PO4 draw solution was only 0.13 g/m2 h, and the specific reverse salt flux was 0.03 g/L using DI water as the feed solution, which are the lowest recorded values among all forward osmosis studies. Hydrophobic attractive interactions between tail groups of Triton X100 with the FO membrane are believed to be the main mechanism for minimizing salt leakage. Results from desalination experiments demonstrated that using 0.55 M Na3PO4 coupled with 0.5 mM Triton X100 as the draw solution and brackish water and seawater as the feed solution with total dissolved solids of 4090 and 36,800 ppm achieved water fluxes of 4.89 L/m2 h and 1.15 L/m2 h, respectively. Furthermore, using a two-stage ultrafiltration–nanofiltration system for the draw solution recovery enabled 98% recovery of solutes.
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The aim of the studies was to analyze the effect of ultrasounds action on osmotic pretreatment and then on drying kinetics in continuous and intermittent drying conditions, and on the final product quality. This paper presents the results of intermittent-convective drying of carrot preceded by ultrasonic assisted osmotic dehydration in fructose aqueous solutions. The theoretical drying kinetics developed from the numerical solution of mathematical model is validated using the experimental data. It has been shown that combination of ultrasonic assisted osmosis with intermittent-convective drying accelerates the drying process and improves the quality of dried biomaterial. A good adherence of the numerically determined kinetic curves confirms the usefulness of the presented model and its possible application to construction of controlled and optimized drying processes.
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This study investigates the performance of an integrated osmotic and microfiltration membrane bioreactor (O/MF-MBR) system for wastewater treatment and reclamation. The O/MF-MBR system simultaneously used microfiltration (MF) and forward osmosis (FO) membranes to extract water from the mixed liquor of an aerobic bioreactor. The MF membrane facilitated the bleeding of dissolved inorganic salts and thus prevented the build-up of salinity in the bioreactor. As a result, sludge production and microbial activity were relatively stable over 60days of operation. Compared to MF, the FO process produced a better permeate quality in terms of nutrients, total organic carbon, as well as hydrophilic and biologically persistent trace organic chemicals (TrOCs). The high rejection by the FO membrane also led to accumulation of hydrophilic and biologically persistent TrOCs in the bioreactor, consequently increasing their concentration in the MF permeate. On the other hand, hydrophobic and readily biodegradable TrOCs were minimally detected in both MF and FO permeates, with no clear difference in the removal efficiencies between two processes. Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.
Article
Solutions to mitigate the reverse diffusion of solutes are critical to the successful commercialisation of the fertiliser drawn forward osmosis process. In this study, we proposed to combine a high performance fertiliser (i.e., ammonium sulfate or SOA) with surfactants as additives as an approach to reduce the reverse diffusion of ammonium ions. Results showed that combining SOA with both anionic and non-ionic surfactants can help in reducing the reverse salt diffusion by up to 67%. We hypothesised that, hydrophobic interactions between the surfactant tails and the membrane surface likely constricted membrane pores resulting in increased rejection of ions with large hydrated radii such as SO4 2−. By electroneutrality, the rejection of the counter ions (i.e., NH4+) also therefore subsequently improved. Anionic surfactant was found to further decrease the reverse salt diffusion due to electrostatic repulsions between the surfactant negatively-charged heads and SO42−. However, when the feed solution contains cations with small hydrated radii (e.g., Na+); it was found that NH4+ ions can be substituted in the DS to maintain its electroneutrality and thus the diffusion of NH4+ to the feed solution was increased.
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Wastewater contains significant amounts of nitrogen that can be recovered and valorized as fertilizers and chemicals. This study presents a new membrane electrode coupled with microbial electrolysis that demonstrates very efficient ammonia recovery from synthetic centrate. The process utilizes the electrical potential across electrodes to drive NH4+ ions towards the hydrophilic nickel top layer on a gas-stripping membrane cathode, which takes advantage of surface pH increase to realize spontaneous NH3 separation and recovery using the membrane electrode structure. Compared with a control configuration with conventionally separated electrode and hydrophobic membrane, the integrated membrane electrode showed 40% higher in NH3-N recovery rate (36.2 ± 1.2 gNH3-N/m2/d) and 11% higher in current density. The energy consumption was 1.61 ± 0.03 kWh/kgNH3-N, which was 20% lower than the control and 70-90% more efficient than competing electrochemical nitrogen recovery processes (5-12 kWh/kgNH3-N). Besides, the negative potential on membrane electrode repelled negatively charged organics and microbes thus reduced fouling. In addition to describing the system’s performance, we explored the underlying mechanisms governing the reactions, which confirmed the viability of this process for efficient wastewater ammonia recovery. Furthermore, the nickel-based membrane electrode showed excellent water entry pressure (∼41 kPa) without leakage, which was much higher than PTFE/PDMS based cathodes (~1.8 kPa). The membrane electrode also showed superb flexibility (180o bend) and can be easily fabricated at low cost (<20 $/m2).
Article
Hollow fiber membranes have shown great promise as a platform for osmotic processes such as forward osmosis (FO) and pressure retarded osmosis (PRO). Numerous hollow fiber FO membranes have been designed by academic researchers around the world. However, few of these designs have made it to full scale production. In this study, we report on the newly launched Aquaporin Inside™ hollow fiber FO membrane from Aquaporin A/S, Denmark. These membranes were tested in miniature modules under various osmotic testing conditions. With incorporating biomimetic aquaporin proteins as “water channel” in the selective layer, these membranes exhibited excellent FO performance with water flux of 21 LMH, reverse salt flux of 3.6 gMH and specific reverse salt flux of 0.18 g/L in PRO mode with 1 M NaCl and deionized water as draw and feed solutions, respectively. The structure parameter was determined to be 210.5 ± 55.5 μm, which is one of the lowest S values reported for thin film composite hollow fiber membranes.
Article
Osmotic microbial fuel cells (OsMFCs) combine the merits of microbial fuel cell (MFC) and forward osmosis (FO) for simultaneous contaminant removal, electricity generation, and high-quality water extraction. As an FO based technology, reverse solute flux (RSF) is one of the key challenges for its operation. Herein, RSF was converted into a positive effect on the system performance by using NaHCO3 solution as a draw solution (DS)/catholyte. It was found that reverse-fluxed NaHCO3 helped buffer the anolyte pH and thus enhance electricity generation, compared to the OsMFC using the NaCl DS/catholyte. At the same concentration, the NaHCO3 DS/catholyte achieved a higher Coulomb production of 1349.2 ± 80.3 C and higher anolyte pH of 6.48 ± 0.19 than those of the NaCl DS/catholyte. At the same conductivity, the NaHCO3 DS/catholyte exhibited better electricity generation performance with a comparable recovered water volume of 417.7 ± 13.7 mL to that of the NaCl DS/catholyte. As the NaHCO3 concentration increased from 0.1 M to 0.75 M, the OsMFC electricity generation was enhanced due to the increased RSF from 19.2 ± 2.3 to 210.8 ± 17.5 mmol m⁻²h⁻¹. In the anode, 92.0 ± 0.8% to 97.1 ± 0.9% of reverse-fluxed NaHCO3 was used to neutralize protons. These results have demonstrated a new strategy that uses the bicarbonate migration driven by both a concentration gradient and electricity generation to successfully raise the alkalinity of the anolyte towards enhancing electricity generation.
Article
Forward osmosis (FO) technology has long been constrained by the slow development of appropriate draw solutes (DS) and the relatively high cost associated with DS recovery. In this study, a series of polyelectrolytes, polyacrylic acid sodium salts (PAA-Na) with different molecular weights, were explored as DS for FO applications with a focus on the recovery using combined pH and microfiltration (MF). The FO system achieved a high water flux of 18.02 ± 0.51 LMH, low reverse salt flux (RSF) of 0.110 ± 0.004 gMH, and the JS/JW of 6.1 ± 0.3 mg L− 1 with 25 wt% PAA-Na (2000 Da) as the DS and DI water as the feed. The DS recovery efficiency by the combined pH + MF approach was 99.68% at pH of 4.35, and the operation cost was estimated at 0.037 $ m− 3. Dynamic light scattering revealed that the hydrodynamic diameter of PAA increased with decreasing pH, resulting in PAA polymers precipitated as aggregates at the pH response point. The 25 wt% 2000 PAA-Na achieved the water flux of 11.56 ± 0.32 LMH from synthetic seawater and 17.19 ± 0.52 LMH from the treated wastewater. These results have demonstrated efficient and cost-effective recovery of PAA DS for FO-based applications.
Article
Recovering valuable resources from wastewater will transform wastewater management from a treatment focused to sustainability focused strategy, and creates the need for new technology development. An innovative treatment concept - osmotic bioelectrochemical system (OsBES), which is based on cooperation between bioelectrochemical systems (BES) and forward osmosis (FO), has been introduced and studied in the past few years. An OsBES can accomplish simultaneous treatment of wastewater and recovery of resources such as nutrient, energy, and water (NEW). The cooperation can be accomplished in either an internal (integrated OsBES) or external (coupled OsBES) configuration, through a strong synergy between BES and FO. BES can provide draw solute, perform pre-treatment, or reduce reverse salt flux to help with FO operation; while FO can achieve water recovery, enhance current generation, and supply energy sources to BES operation. Given much progress and interest in the OsBES, this paper has reviewed the past studies, described the current status, presented qualitative and quantitative analyses, and discussed the perspectives of the OsBES technology with a focus on NEW recovery from wastewater. The challenges for further researching and developing OsBES have also been identified.
Article
The pressure assisted osmosis (PAO) process has been recently considered as a new strategy to enhance water flux and to limit reverse salt transport (RST), hereby overcoming two critical limitations of forward osmosis (FO) operation through the use of additional pressure on the feed side. With the aim to achieve higher (economically sustainable) fluxes, the use of commercially available nanofiltration (NF) membranes under PAO operating conditions is considered for the first time in this study. When operated under PAO mode, the tested commercial NF membranes clearly outperform the state of the art FO membrane with fluxes up to 36 L m⁻² h⁻¹ and RST below 0.01 g L⁻¹, demonstrating the relative potential of PAO-NF. For flat sheet NF membrane osmotic contribution was minimal due to intense internal concentration polarisation. However, the tested hollow fiber NF membrane allowed for low internal concentration polarisation and exhibited significant flux even in FO operation. However, transmission of salts from feed to draw solutions (forward salt transport, FST) also occurred and was observed to be linearly proportional with the NF top layer rejection. Therefore, it is an important parameter to consider in the membrane selection in addition to the trade-off between large flux and low RST. The PAO-NF concept also proved to be more efficient in terms of water flux than direct NF operation, owing to a small but significant contribution of osmotic pressure. A modelling study demonstrated that further flux enhancement could be obtained through modification of NF membranes support layer to improve the osmotic contribution. These encouraging initial results warrant the need for a more detailed assessment of the long-term operation and energy requirement of the PAO-NF concept for a range of industrial applications.
Article
Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell - forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9% of water (70.4 ± 2.4 mL), 99.7 ± 13.0% of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N2 stripping), and 79.5 ± 0.5% of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5% of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m−3 treated centrate, 0.57 ± 0.04 kWh kg−1 COD, 1.10 ± 0.05 kWh kg−1 removed NH4+-N, 1.17 ± 0.06 kWh kg−1 recovered NH4+-N, or 5.75 ± 0.54 kWh kg−1 struvite. Recycling of excess Mg2+ reduced its dosage to 0.08 kg Mg2+/kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.
Article
Abstract Forward osmosis (FO) is an alternative approach for treating landfill leachate with potential advantages of reducing leachate volume and recovering high quality water for direct discharge or reuse. However, energy consumption by FO treatment of leachate has not been examined before. Herein, the operational factors such as recirculation rates and draw concentrations were studied for their effects on the quantified energy consumption by an FO system treating actual leachate collected from two different landfills. It was found that the energy consumption increased with a higher recirculation rate and decreased with a higher draw concentration, and higher water recovery tended to reduce energy consumption. The highest energy consumption was 0.276 ± 0.033 kW h m−3 with the recirculation rate of 110 mL min−1 and 1-M draw concentration, while the lowest of 0.005 ± 0.000 kW h m−3 was obtained with 30 mL min−1 recirculation and 3-M draw concentration. The leachate with lower concentrations of the contaminants had a much lower requirement for energy, benefited from its higher water recovery. Osmotic backwashing appeared to be more effective for removing foulants, but precise understanding of membrane fouling and its controlling methods will need a long-term study. The results of this work have implied that FO treatment of leachate could be energy efficient, especially with the use of a suitable draw solute that can be regenerated in an energy efficient way and/or through combination with other treatment technologies that can reduce contaminant concentrations before FO treatment, which warrants further investigation.
Article
Forward osmosis (FO) has been widely studied for desalination or water recovery from wastewater, and one of its key challenges for practical applications is reverse solute flux (RSF). RSF can cause loss of draw solutes, salinity build-up and undesired contamination at the feed side. In this study, in-situ electrolysis was employed to mitigate RSF in a three-chamber FO system (“e-FO”) with Na2SO4 as a draw solute and deionized (DI) water as a feed. Operation parameters including applied voltage, membrane orientation and initial draw concentrations were systematically investigated to optimize the e-FO performance and reduce RSF. Applying a voltage of 1.5 V achieved a RSF of 6.78 ± 0.55 mmol m−2 h−1 and a specific RSF of 0.138 ± 0.011 g L−1 in the FO mode and with 1 M Na2SO4 as the draw, rendering ∼57% reduction of solute leakage compared to the control without the applied voltage. The reduced RSF should be attributed to constrained ion migration induced by the coactions of electric dragging force (≥1.5 V) and high solute rejection of the FO membrane. Reducing the intensity of the solution recirculation from 60 to 10 mL min−1 significantly reduced specific energy consumption of the e-FO system from 0.693 ± 0.127 to 0.022 ± 0.004 kWh m−3 extracted water or from 1.103 ± 0.059 to 0.044 ± 0.002 kWh kg−1 reduced reversed solute. These results have demonstrated that the electrolysis-assisted RSF mitigation could be an energy-efficient method for controlling RSF towards sustainable FO applications.
Article
We investigated the possible underlying mechanism of the low fouling potential in the forward osmosis (FO) process during the osmotic dilution of seawater as part of the simultaneous desalination and wastewater reuse by FO and reverse osmosis hybrid system. Long-term experiments revealed an interesting water flux pattern highly dependent on the different operating parameters. The most interesting observation made was the spontaneous increase in the FO permeate flux at regular time interval during the FO operation using synthetic wastewater as feed and seawater. This sinusoidal FO flux pattern related well with the build-up of loose fouling layer and their natural peel-off from the membrane surface upon reaching certain layer thickness due to crossflow velocity shear. This flux pattern was more prominent at higher cross-flow velocity rates, lower feed water pH, for a smoother membrane surface and at lower operating pressure during pressure assisted osmosis (PAO) mode. Based on these results, membrane cleaning strategies were proposed by targeting a higher cross-flow velocity shear at a time when the permeate flux started to just increase. The approach of physical membrane cleaning was observed efficient and was able to almost fully restore the initial flux even under the PAO operation at 4 bar.
Article
We explored the specific role of reverse solute diffusion (RSD) on the scaling in osmotically-driven membrane processes (particularly forward osmosis (FO)). Both scaling precursors (e.g., Ca2 + and phosphate) and anti-scaling precursors (e.g., H⁺ and a chelating agent ethylenediamine tetraacetic acid (EDTA)) were used to investigate the effect of RSD and draw solution chemistry on calcium phosphate scaling. While draw solutions containing Ca2 + tend to promote calcium phosphate scaling, this effect was noticeable only if the specific RSD of Ca2 + (i.e., the ratio of Ca2 + flux to water flux) was greater than the original Ca2 + concentration in the feed water. The RSD of H⁺ and EDTA effectively suppressed scaling. For the first time, we demonstrated a new scaling control strategy for FO by the inclusion of anti-scaling functions in the draw solution chemistry. Our work has important implications for the design and operation of FO processes.