Spiral Wound Forward Osmosis Research Articles

The influence of engineering factors on the efficiency of a spiral wound forward osmosis system: Performance and economic evaluation

Three different scale commercialized spiral wound (SW) type forward osmosis (FO) elements were evaluated. Each element has a unique optimum operating condition, because operating conditions depend on the dimension, performance and element design factor. These factors determine the operating conditions and plant capacity of the SWRO process. This study evaluates the effect of the size in SWFO element via performance evaluation and economic analysis. Moreover, investigation of engineering factors for possible commercialization of SWFO-RO hybrid system was also carried out. Investigation of engineering effect and process economic impact is essential stage for system implication and technology step up. For each element size, maximum FS recovery, DS dilution rates and water flux were highly dependent on the varying design factors. The maximum FS recovery rate were 37.2 and 62.6%; the DS dilution rates were 62.6% for 2540 and 8040 SW, respectively. The water flux for 2540 and 8040 SW elements were 27.6 and 21.1 LMH, respectively Nevertheless, 8040 is 24% more economically than 2540 because of the 8040 can satisfy the minimum requirement of capital cost factors. Nevertheless, 8040 is 24% more economical than 2540 because 8040 can satisfy the minimum requirement of the capital cost factors.

Performance Comparison of Spiral-Wound and Plate-and-Frame Forward Osmosis Membrane Module.

We compared two representative forward osmosis (FO) modules—spiral-wound (SW) and plate-and-frame (PF)—to provide practical information for the selection of FO element for a large-scale FO process. The FO operating performance of commercially available SW FO and PF FO was explored under different membrane area and flow rate conditions. The performance trend as a function of the membrane was obtained by adjusting the number of serially connected elements. Although SW FO and PF FO elements exhibited comparable feed pressure drops, SW FO demonstrated a significantly higher draw channel pressure drop than PF FO. Furthermore, the significant draw pressure drop in SW FO increased the draw inlet pressure, consequently limiting the number of serially connected elements. For example, the maximum number of serially connected elements for the normal operation was three elements for SW FO (45.9 m2) but nine elements for PF FO (63 m2) when the flow rate of 10 LMP was applied for feed and draw streams. Additionally, a footprint analysis indicated that SW FO module exhibited a slightly larger footprint than PF FO. Under investigated conditions, PF FO exhibited relatively better performance than SW FO. Therefore, this pilot-scale FO study highlighted the need to reduce the flow resistance of SW FO draw channel to take advantage of the high packing density of the SW element.

Influence of hydrodynamic operating conditions on organic fouling of spiral-wound forward osmosis membranes: Fouling-induced performance deterioration in FO-RO hybrid system

The forward osmosis-reverse osmosis (FO-RO) hybrid process has been extensively researched as part of attempts to reduce the high energy consumption of conventional seawater reverse osmosis in recent years. FO operating conditions play a substantial role in the hybrid process, dictating not only the performance of the entire system but also the propensity for fouling, which deteriorates performance in long-term field operations. Therefore, determining the optimal FO operating conditions with regard to membrane fouling may promote sustainable operation through efficient fouling control. This study thus evaluated the influence of each hydrodynamic operating condition (feed flowrate, draw flowrate, and hydraulic pressure difference) and their synergistic effects on fouling propensity in a pilot-scale FO operation under seawater and municipal wastewater conditions. Fouling-induced variation in water flux, channel pressure drop, diluted concentration, and the resulting specific energy consumption (SEC) were comparatively analyzed and utilized to project performance variation in a full-scale FO-RO system. Fouling-induced performance reduction significantly varied depending on hydrodynamic operating conditions and the resultant fouling propensity during 15 days of continuous operation. A high feed flowrate demonstrated a clear ability to mitigate fouling-induced performance deterioration in all conditions. A high draw flowrate turned out to be detrimental for fouling propensity since its high reverse solute flux accelerated fouling growth. Applying additional hydraulic pressure during FO operation caused a faster reduction of water flux, and thus feed recovery and water production; however, these drawbacks could be compensated for by a 10% reduction in the required FO membrane area and an additional reduction in RO SEC.

Exploring the Operation Factors that Influence Performance of a Spiral-Wound Forward Osmosis Membrane Process for Scale-up Design.

Forward osmosis (FO) technology has increasingly attracted attention owing to its low operational energy and low fouling propensity. Despite extensive investigations on FO, very few module-scale FO studies on the operation and design of the FO process have been conducted. In this paper, a simple and practical FO process design parameter called normalized membrane area is suggested based on a performance analysis of spiral-wound FO elements. The influence of operation factors on operating pressures and water recovery was investigated using 8-inch spiral wound elements in the continuous operation mode. The membrane area was adjusted by series connection of FO elements to a maximum value of 46 m2 (three elements). The feed and draw flow rates were varied between 5 and 15 LPM under various feed (10, 20, and 30 g/L) and draw (58.4 and 233.8 g/L) concentration combinations. The analysis of flow rates (feed, draw, and permeate flow rates) indicated not only high flow channel resistance on the draw side but also high permeate flow rates can induce higher operating pressures owing to strong mutual interaction of the feed and the draw streams. Feed water recovery was focused on as a key performance index, and the experimental recovery (RExp) and theoretical maximum recovery (RTh) values were compared. The results revealed the significance of the feed flow rate and the membrane area in terms of enhancing the water recovery performance. In addition, a clear relationship was observed between the membrane area normalized by the initial feed flow rates and the water recovery ratio (RExp/RTh), even though the applied operation conditions were different. Finally, an empirical equation to estimate the required membrane area of spiral-wound FO was proposed for the FO process design. The equation can be used to predict water recovery of FO systems as well, for example, if an FO system is operated at 0.08 m2L−1h of the normalized membrane area, the system is expected to offer 78% of the RTh value.

Techno-economic evaluation of an element-scale forward osmosis-reverse osmosis hybrid process for seawater desalination

The forward osmosis (FO)-reverse osmosis (RO) hybrid process is gaining attention in the desalination market because it can purify diluted seawater and the RO unit functions at low pressure conditions, resulting in a reduced total operational cost. However, FO element configuration affects the process performance, minimum flow rate, inlet pressure, product capacity, and draw solution (DS) dilution rate. Moreover, economic evaluation of the FO-RO hybrid process in the Middle East, which is the largest seawater desalination market, is required to obtain representative results. Realistic economic evaluation can be achieved with a real-performance database (DB) and specific assumptions. In this study, a techno-economic evaluation of the FO-RO hybrid process was conducted using real element-scale FO DB and simulation DB, and the results were compared with those of a stand-alone two stage RO process. Spiral wound FO (SWFO) and plate and frame (PFFO)-RO hybrid processes were more economical by 8.84% and 3.73%, respectively, when compared to two-stage RO. In the Middle East, the total cost of SWFO-RO was 45.1 M$ lesser than that of PFFO-RO due to its higher water flux and DS dilution rate. Therefore, the FO-RO hybrid process has high economic potential in the Middle East and elsewhere.

Fouling and transport of organic matter in cellulose triacetate forward-osmosis membrane for wastewater reuse and seawater desalination

Forward osmosis (FO) can extract water from a solution with a low chemical potential (feed solution, FS) and transport it to a solution with a high chemical potential (draw solution, DS) through natural osmotic pressure. For wastewater reuse via FO, an identifying the foulants and understanding the fouling and transport mechanisms are important. An element-scale spiral-wound FO (SWFO) system and a laboratory-scale FO module tests were conducted with a cellulose triacetate-based FO membrane. Secondary wastewater effluent was used as the FS. To determine the main foulants in FO, the element-scale SWFO was operated at a wastewater plant for 36 d, and a detailed characterization of the foulants (particularly organic matters; OMs) and a membrane autopsy were conducted. The results were verified via a laboratory-scale demonstration. Hydrophilic and large-molecular-weight OMs was the main foulant. It was transported to the DS from the FS through the membrane. The water flux, reverse solute flux, and related parameters (type, concentration, and valence of the draw solute) affected the transport of OMs through the FO membrane. Therefore, further study is needed to develop strategies for reducing the transportation of OMs through the membrane in the wastewater reuse by selecting a suitable draw solute or properly arranging the elements.

A simple modeling approach for a forward osmosis system with a spiral wound module

A simple but accurate prediction method for the performance of a commercial spiral wound forward osmosis (FO) module was developed. The method includes a fundamental model based on the internal and external concentration polarization (ICP and ECP) in the FO process, the module experiments with sodium chloride, and a fitting process to increase the accuracy of the model. Comparison between the ICP/ECP modeling results and the experimental data reveals that trans-membrane pressure is a key parameter to explain the difference between the modeling and experimental results. The draw solution (DS) channel heights in the module could be shrunk by trans-membrane pressure, and this hypothesis is strongly supported by a statistical analysis for the differential pressure and the accuracy of a modified model accounting for the effect of trans-membrane pressure. The modified model with trans-membrane pressure and other hydrodynamic factors as fitting variables predicts the performance of the spiral wound FO module accurately. The number of experimental data for the fitting process (i.e., trained data) to obtain a reliable prediction model was found to be around 30, and the modified model turns out to work reasonably well to predict not only the trained data but also the untrained data.

Draw channel contraction of an 8040 spiral-wound forward osmosis membrane element in pressure-assisted forward osmosis (PAFO)

Draw channel contraction of an 8040 spiral-wound forward osmosis membrane element in pressure-assisted forward osmosis (PAFO)

Feasibility evaluation of element scale forward osmosis for direct connection with reverse osmosis

Forward osmosis (FO) and reverse osmosis (RO) hybrid process is taking center stage under the international spotlight in water treatment and desalination industries. Nevertheless, most existing researches are on the lab-scale and only few researches have been done on the element-scale. Currently, two types of elements are available, spiral wound FO (SWFO) and flat sheet FO (FSFO). However their performances have not yet been clearly addressed or compared. In addition, there is no research of which type of FO element is suitable for FO-RO hybrid process for wastewater treatment and desalination. Therefore, this paper investigated to find the main factors that need to be considered for scale-up with lab-scale and element-scale experiments under different operational conditions (draw solution (DS) concentration, and flow rates of feed and draw side). For SWFO, it is limited in the changing operating conditions due to its structural characteristic. However, FSFO is relatively free to change operating conditions and the flow rate difference also show a positive effect on the FO performance (water fluxes at 20 and 30L/min with 0.5M of DS were around 6.0 and 13.7L/m2h, respectively). Through the scenario of serial stage for scale-up, the volume of DS, it was found that the final concentration of DS, and the inlet pressure are the important factors for determining the suitability of FO element.

Organic fouling characterization of a CTA-based spiral-wound forward osmosis (SWFO) membrane used in wastewater reuse and seawater desalination

This research explores initial organic membrane fouling of element-scale spiral-wound forward osmosis (SWFO) operated at a wastewater plant using real secondary wastewater effluent (SWWE) as feed solution (FS) and synthetic seawater as draw solution (DS). The SWFO was operated long-term and the average water flux reduced from 6.0 to 3.2 L/m2·h. After the operation, membrane samples were taken from three locations in the SWFO element (i.e., inlet, middle, and outlet) to study the structural effects of organic membrane fouling. The membrane foulants were extracted in sodium hydroxide and deionized water to characterize irreversible and reversible organic foulants, respectively. Organic matter (OM) contained in the FS was dominated by hydrophilic (HPI) aromatic proteins (molecular weights (MWs) of 30,000 Da) and soluble microbial byproducts (which are associated with humic substances and have MWs of 920–2000 Da). The highest organic content (2.67 mg-C/cm2) was found in the inlet of the SWFO element and, interestingly, was mostly irreversible. In the inlet, humic- or fulvic-like organics and aromatic proteins were dominant, while higher protein-like organics were detected in the middle and the outlet of the element. The organic fouling behavior of the SWFO membrane can be explained as follows: HPI OM formed the initial, irreversible fouling on the membrane surface, after which the hydrophobic (HPO) OM, which is reversible, attached to the initially formed HPI fouling layer by electric interaction dominantly. Therefore, HPI organic foulants should be controlled to reduce irreversible fouling and subsequently guarantee the sustainable operation of SWFO in the SWWE treatment.

Effect of transmembrane pressure on draw solution channel height and water flux in spiral wound forward osmosis module

Effect of transmembrane pressure on draw solution channel height and water flux in spiral wound forward osmosis module

Experimental study of a cellulose triacetate spiral wound forward osmosis membrane for desalination process integration

Experimental study of a cellulose triacetate spiral wound forward osmosis membrane for desalination process integration

Effect of initial feed and draw flowrates on performance of an 8040 spiral-wound forward osmosis membrane element

Effect of initial feed and draw flowrates on performance of an 8040 spiral-wound forward osmosis membrane element

Practical considerations for operability of an 8″ spiral wound forward osmosis module: Hydrodynamics, fouling behaviour and cleaning strategy

A better understanding of large spiral wound forward osmosis (SW FO) module operation is needed to provide practical insight for a full-scale FO practical implementation desalination plant. Therefore, this study investigated two different 8″ SW FO modules (i.e. cellulose tri acetate, CTA and thin film composite, TFC) in terms of hydrodynamics, operating pressure, water and solute fluxes, fouling behaviour and cleaning strategy. For both modules, a significantly lower flow rate was required in the draw channel than in the feed channel due to important pressure-drop in the draw channel and was a particularly critical operating challenge in the CTA module when permeate spacers are used. Under FO and pressure assisted osmosis (PAO, up to 2.5bar) operations, the TFC module featured higher water flux and lower reverse salt flux than the CTA module. For both modules, fouling tests demonstrated that feed inlet pressure was more sensitive to foulant deposition than the flux, thus confirming that FO fouling deposition occurs in the feed channel rather than on the membrane surface. Osmotic backwash combined with physical cleaning used in this study confirmed to be effective and adapted to large-scale FO module operation.

Performance evaluation of two-stage spiral wound forward osmosis elements at various operation conditions

AbstractForward osmosis (FO) is an emerging process in water industry for wastewater treatment, water reuse, and desalination. Although many lab-scale studies have been done, the data generated cannot be directly applied to a real pilot plant due to different membrane configuration and operating conditions. In this study, we evaluated commercial spiral wound forward osmosis (SWFO) elements in various operating conditions (draw solution concentration, flow rate, and element array type). First, we investigated the SWFO special structure (winding configuration of the draw flow path). Due to the structural characteristics of SWFO, the draw flow rate showed a high-pressure drop effect because of feed flow rate. Second, we studied the performance of different element array types. Both sides of flow rate change influenced the performance of pilot-scale SWFO by reducing concentration polarization and dilution effect. In addition, according to the type of SWFO element array, the flow rate had different role in wat...

Investigation of pilot-scale 8040 FO membrane module under different operating conditions for brackish water desalination

Two spiral wound forward osmosis membrane modules with different spacer designs (corrugated spacer [CS] and medium spacer [MS]) were investigated for the fertilizer-drawn forward osmosis (FO) desalination of brackish groundwater (BGW) at a pilot-scale level. This study mainly focused on examining the influence of various operating conditions such as feed flow rate, total dissolved solids (TDS) concentration of the BGW feed, and draw solution (DS) concentrations using ammonium sulfate ((NH4)2SO4, SOA) on the performance of two membrane modules. The feed flow rate played a positive role in the average water flux of the pilot-scale FO membrane module due to enhanced mass transfer coefficient across the membrane surface. Feed TDS and DS concentrations also played a significant role in both FO membrane modules because they are directly related to the osmotic driving force and membrane fouling tendency. CS module performed slightly better than MS module during all experiments due to probably enhanced mass transfer and lower fouling propensity associated with the CS. Besides, CS spacer provides larger channel space that can accommodate larger volumes of DS, and hence, could maintain higher DS concentration. However, the extent of dilution for the CS module is slightly lower.

Towards direct potable reuse with forward osmosis: Technical assessment of long-term process performance at the pilot scale

In this study we evaluated the performance of forward osmosis (FO) at the pilot scale to achieve simultaneous seawater desalination and wastewater reclamation. The investigation was performed with a commercial spiral wound FO membrane element for approximately 1300h of continuous operation, processing 900,000L of wastewater effluent and producing 10,000L of purified water through a hybrid FO-RO process. Water and solute fluxes were monitored during the study. Reversible and irreversible membrane fouling was observed; however, water flux was maintained at a relatively constant rate of 5.7±0.2Lm−2h−1 with MBR permeate feed and seawater draw solution. Subsequent increase of total suspended solids (TSS) concentration in the FO feed (secondary treated effluent with 5 to 16mgL−1 TSS) resulted in incremental flux decline; however, the membrane typically achieved stable water flux after the initial exposure to foulants. Additional analysis focused on bi-directional transport of inorganic species and a detailed evaluation of dissolved organic matter permeation through the membranes in the hybrid process. Evaluation of sample fluorescence revealed that the FO membrane and the hybrid process provide a strong barrier to protein-like fluorophores associated with wastewater effluent. Results also demonstrated the robust nature of dual barrier membrane systems to achieve greater than 99.9% removal of orthophosphate and dissolved organic carbon and more than 96% rejection of nitrate. Upon completion of the study a comprehensive membrane autopsy was performed on the FO and RO membranes. Organic fouling on the FO membrane was observed to have low adhesion to the membrane surface, but did result in some modification to membrane active layer properties.

Effect of draw solution type and operational mode of forward osmosis with laboratory-scale membranes and a spiral wound membrane module

Forward osmosis (FO) is a concentration driven membrane process which recently gained an increase in attention due to the development of improved FO membranes. Most of the currently available data on FO research is obtained on small laboratory-scale set-ups, thereby overlooking the effects of scaling-up to pilot or full-scale size. In this paper, FO experiments are carried out with a 10.16 cm (4-in) spiral wound FO (SWFO) Hydration Technologies Innovations (HTI) module. The performance of the SWFO module was investigated during daily experiments and the influence of two types of draw solutions (NaCl and MgCl2) was evaluated and compared to data from lab-scale FO research. Furthermore, the difference between fixed draw solution concentration and draw solution dilution was studied for both draw solutions. Salt flux was determined from the increase in: (i) conductivity; and (ii) individual ion concentration in the feed vessel. Water and salt flux values from laboratory-scale membrane FO experiments were similar but slightly lower than that of the SWFO module in the fixed draw solution concentration experiments (respectively 5 L/m2h and 3 g/m2h for 0.5 M NaCl). Salt flux values obtained from individual ion measurements were lower and more accurate compared to that determined by conductivity measurements.

Experimental Study of a 4040 Spiral-Wound Forward-Osmosis Membrane Module

This paper analyzes the structural features of a spiral-wound forward-osmosis (SW FO) membrane module via an experimental approach and presents the relationships between the water flux and operating conditions for design and operation of a large-scale FO process. The SW FO module has four ports: an inlet/outlet for the draw solution and an inlet/outlet for the feed solution. Accordingly, two strongly interacting flow streams existed on either side of the membrane with spatially variable properties. Unlike the operation of a membrane cell device loaded with a small membrane coupon, it was appropriate to operate a housing-type FO unit loaded with a 4040 SW FO module with a lower draw flow rate than feed flow rate. Because of the structural features of the SW FO module, the draw solution flowed inside of the membrane envelope under a considerable pressure in order to overcome the flow resistance. The effect of operating conditions on the water flux in a 4040 SW FO module was investigated. A water flux equation based on a temperature-correction factor (TCF) was proposed to predict the water flux at a given temperature. Our study is a good reference point for designing the FO process and FO membrane module.

Effect of draw solution concentration and operating conditions on forward osmosis and pressure retarded osmosis performance in a spiral wound module

Forward osmosis (FO) and pressure retarded osmosis (PRO) are concentration-driven membrane processes. While they can be potentially used in water, wastewater, and energy applications, these processes suffer from the concentration polarization inside the porous membrane support resulting in severe flux decrease, a phenomenon known as internal concentration polarization (ICP). Researchers have investigated the effect of ICP both in theoretical and experimental studies. The current study extends the existing ICP model to include the effect of draw solution dilution by membrane permeate flow in a spiral wound FO module (SWFO). FO and PRO experiments were performed using a Hydrowell ® SWFO under both submerged and cross-flow conditions. The effect of draw solution concentration, draw solution flow rate, feed water flow rate, and membrane orientation on FO and PRO water flux performance was systematically investigated. Permeate flow increased with greater draw solution concentration in both FO and PRO modes. ICP was found to drastically limit the available membrane flux in the concentration-driven membrane processes, and its adverse effect was more severe at greater draw solution concentration. Membrane flux was also affected by the dilution of draw solution when the permeate flow rate was comparable or greater than the draw solution flow rate. The submerged FO configuration performed nearly as good as the cross-flow configuration with feed water circulating outside of the membrane envelope (shorter flow path). In this case, the feed water flow rate only had limited effect on membrane flux likely due to its low mass transfer resistance. In contrary, the membrane flux can be adversely affected at low feed water flow rate when it was circulated inside of the membrane envelope (longer flow path).