Pressure-assisted Forward Osmosis Research Articles

Evaluation of pressure-assisted forward osmosis for concentrating desalination brine: a feasibility study

Evaluation of pressure-assisted forward osmosis for concentrating desalination brine: a feasibility study

Forward osmosis (FO)-reverse osmosis (RO) hybrid process incorporated with hollow fiber FO

Currently, desalination is limited by high energy consumption and high operational and maintenance costs. In this study, a new concept of a hollow fiber forward osmosis (HFFO)-based infinity desalination process with minor environmental impacts (free-energy intake and no pretreatment or brine discharge) is suggested. To evaluate the concept, an element-scale HFFO was conducted in both conventional FO and pressure-assisted FO modes, simulating a submerged HFFO operation. In the HFFO test, the impacts of several operating conditions on the performance of the HFFO were investigated to select the best case. Based on these results, the energy costs were calculated and compared with those of a hybrid FO–seawater reverse osmosis (SWRO) process. The HFFO showed a high dilution rate of the draw solution (up to approximately 400%), allowing the downstream SWRO process to operate at 25 bar with the same permeate volume production (recovery rate of 60%). Consequently, the HFFO-based infinity desalination process has an annual energy revenue of 183.83 million USD, compared with a stand-alone two-stage RO process based on a 100,000 m3/day plant.

Performance of the Pressure Assisted Forward Osmosis-MSF Hybrid Desalination Plant

An osmotically driven membrane process was proposed for seawater pretreatment in a multi-stage flashing (MSF) thermal plant. Brine reject from the MSF plant was the draw solution (DS) in the forward osmosis (FO) process in order to reduce chemical use. The purpose of FO is the removal of divalent ions from seawater prior the thermal desalination. In this study, seawater at 80 g/L and 45 g/L concentrations were used as the brine reject and seawater, respectively. The temperature of the brine reject was 40 °C and of seawater was 25 °C. Commercial thin-film composite (TFC) and cellulose triacetate (CTA) membranes were evaluated for the pretreatment of seawater in the FO and the pressure-assisted FO (PAFO) processes. Experimental results showed 50% more permeation flux by increasing the feed pressure from 1 to 4 bar, and permeation flux reached 16.7 L/m2h in the PAFO process with a TFC membrane compared to 8.3 L/m2h in the PAFO process with CTA membrane. TFC membrane experienced up to 15% reduction in permeation flux after cleaning with DI water while permeation flux reduction in the CTA membrane was >6%. The maximum recovery rate was 11.5% and 8.8% in the PAFO process with TFC and CTA membrane, respectively. The maximum power consumption for the pretreatment of seawater was 0.06 kWh/m3 and 0.1 kWh/m3 for the PAFO process with a TFC and CTA membrane, respectively.

Insight into fouling potential analysis of a pilot-scale pressure-assisted forward osmosis plant for diluted seawater reverse osmosis desalination

In recent years, pressure-assisted forward osmosis (PAFO) process has been studied to overcome the low water productivity in FO-RO hybrid seawater desalination. Our research group demonstrated a pilot-scale PAFO-RO plant for seawater desalination operations using secondary treated wastewater and natural seawater. A pretreatment stage of mesh tube filter media (MTF) and cartridge filter (CF) was implemented for a pilot-scale PAFO. In this study, the water quality and fouling index (SDI15 and MFI0.45) of the influent and treated water at each process stage of the plant were measured. For the influent of both wastewater and seawater feature, it showed linear correlations between the concentration of microbial ATP (i.e., an indicator of microbial activity) and MFI0.45. After the PAFO was operated for 76 days, the fouling of the filtration media and the FO membrane was also analyzed. The observation of the fouled membranes by SEM showed that fouling was hardly observed on the side contacting with seawater, but severe bacterial biofilms were observed on the side contacting with wastewater. FT-IR results also confirmed protein-like substances on the membrane surface contacting with wastewater, indicating irreversible fouling. This study suggests that an advanced pretreatment process to remove bacteria and organic matter is essential for the protection of the FO membranes.

Performance Evaluation and Fouling Propensity of Forward Osmosis (FO) Membrane for Reuse of Spent Dialysate.

The number of chronic renal disease patients has shown a significant increase in recent decades over the globe. Hemodialysis is the most commonly used treatment for renal replacement therapy (RRT) and dominates the global dialysis market. As one of the most water-consuming treatments in medical procedures, hemodialysis has room for improvement in reducing wastewater effluent. In this study, we investigated the technological feasibility of introducing the forward osmosis (FO) process for spent dialysate reuse. A 30 LMH of average water flux has been achieved using a commercial TFC membrane with high water permeability and salt removal. The water flux increased up to 23% with increasing flowrate from 100 mL/min to 500 mL/min. During 1 h spent dialysate treatment, the active layer facing feed solution (AL-FS) mode showed relatively higher flux stability with a 4–6 LMH of water flux reduction while the water flux decreased significantly at the active layer facing draw solution (AL-DS) mode with a 10–12 LMH reduction. In the pressure-assisted forward osmosis (PAFO) condition, high reverse salt flux was observed due to membrane deformation. During the membrane filtration process, scaling occurred due to the influence of polyvalent ions remaining on the membrane surface. Membrane fouling exacerbated the flux and was mainly caused by organic substances such as urea and creatinine. The results of this experiment provide an important basis for future research as a preliminary experiment for the introduction of the FO technique to hemodialysis.

Membrane transport behavior characterization method with constant water flux in pressure-assisted forward osmosis

In this study, a new membrane transport behavior characterization method using constant water flux in a pressure-assisted forward osmosis (PAFO) was developed. The constant water flux was realized by superimposing a hydraulic pressure on the concentration gradient to follow the target water flux. The pump adjusts its hydraulic pressure automatically to compensate for the target flow rate (water flux) which is insufficient by the concentration gradient itself. The constant water flux makes the method relieve the complex correlation between the water flux and the concentration gradient in theoretical models. Using the developed method, we characterized various properties that correlate with membrane transport behavior, such as mass transfer coefficient, structure parameter, diffusion coefficient, and reverse salt flux. The biggest advantage of the method is the continuous measurement of various membrane transport behavior properties by changing solution concentration with acceptable accuracy. In most cases, validation experiments showed that the proposed method can estimate the various membrane transport behavior properties under ±10% error (<5% in case of diffusion coefficient) in a wide range of concentrations. In conclusion, the proposed method can be utilized as a continuous, multifunctional, and less laborious method for membrane transport behavior characterization.

The relevance of critical flux concept in the concentration of skim milk using forward osmosis and reverse osmosis

Skim milk was concentrated at 10 °C using forward osmosis (FO), reverse osmosis (RO) and pressure-assisted forward osmosis (PAFO). A pressure of 40 bar, in the form of draw solution osmotic pressure (FO and PAFO modes) or transmembrane hydraulic pressure (RO mode) was applied; an additional hydraulic pressure of 2 bar was applied in the PAFO mode. More severe protein fouling was observed in RO, followed by PAFO and then FO. This was credited to the difference in the initial permeate flux, induced by the different effective driving pressures, with RO having a greater deviation of the initial flux from the critical flux value. The critical flux was determined for the FO and RO modes using a step-wise increase of draw solution osmotic pressure or hydraulic pressure, at a constant milk solids content. The critical flux was between 5.4 L/m2h (1.5 × 10−6 m3/m2s) and 7.2 L/m2h (2 × 10−6 m3/m2s) for both the FO and RO modes at a cross flow velocity of 0.2 m/s. The similarities in the critical flux for FO and RO suggests that the critical flux does not depend on the nature of pressure applied on the system (hydraulic or osmotic). Therefore, when operated at the same flux and crossflow velocity, FO would not fundamentally provide a lower fouling environment compared to RO. An increase of the solids content from 8.7% to 17.3% caused a reduction in the critical flux from 5.4 L/m2h to 3.1 L/m2h (8.5 × 10−7 m3/m2s).

Performance analysis of serially-connected membrane element for pressure-assisted forward osmosis: wastewater reuse and seawater desalination

Performance analysis of serially-connected membrane element for pressure-assisted forward osmosis: wastewater reuse and seawater desalination

Corrigendum to "Performance analysis of serially-connected membrane element for pressure-assisted forward osmosis: wastewater reuse and seawater desalination" published in vol. 183, April 2020, pp. 104-113 (doi:10.5004/dwt.2020.25260)

Corrigendum to "Performance analysis of serially-connected membrane element for pressure-assisted forward osmosis: wastewater reuse and seawater desalination" published in vol. 183, April 2020, pp. 104-113 (doi:10.5004/dwt.2020.25260)

Cost-oriented optimization of osmotic dilution based on concentration-dependent hydraulic pressure

Osmotic dilution (OD) has been integrated with mainstream seawater reverse osmosis (SWRO) desalination technology to eliminate the worry about the draw solution regeneration and simultaneously lower the desalination cost. In this study, we further optimize the OD design with regard to mitigated water flux decline by introducing the concentration-dependent hydraulic pressure and developing one module-level techno-economic model. Analysis of the module-scale model firstly indicates that simply increasing the flowrate ratio of the feed solution stream to the draw solution stream is not economically applicable to mitigate the inherent water flux behavior in OD, potentially highlighting the significance of concentration-dependent hydraulic pressure. Accordingly, one-stage or multi-stage pressure-assisted forward osmosis (PAFO) followed by OD is evaluated its techno-economic advantage compared to the original OD process, respectively. Simulation results show that, for applied commercial FO membrane, OD combined with one-stage PAFO is the optimal design that balances the mitigated water flux decline with maximum saving and strongly depends on the permeate flow. But, future improved FO membranes necessitate the systematic exploration due to the fact that the optimal OD design is also affected by the membrane transport parameters. Therefore, this work can provide a protocol to optimize the OD design in seawater desalination.

Serially connected forward osmosis membrane elements of pressure-assisted forward osmosis-reverse osmosis hybrid system: Process performance and economic analysis

Due to the improved dilution of draw streams, employing pressure-assisted forward osmosis (PAFO) to the hybrid system of forward osmosis (FO) followed by reverse osmosis (RO) for seawater desalination has been expected to reduce the overall economics. However, replacing FO with PAFO causes an additional energy cost in the seawater dilution step which inevitably leads to a question that PAFO-RO hybrid is truly an economically beneficial option. More importantly, though serial connection of FO elements improves the dilution of initial draw water, this economic benefit is also compensated with the additional membrane. To rationalize its overall performance and economic benefit, thorough performance and economic evaluations were conducted based on actual pilot-scale PAFO operations for serial connection of up to three 8040 FO elements. The results showed the FO-RO hybrid is not an economically feasible option unless a significant unit FO element cost cut-down is guaranteed. Meanwhile, PAFO-RO showed benefits with regards to target RO recovery and unit FO element cost, particularly when two FO elements are serially connected (SE2). It was found that PAFO-RO, indeed, has higher economic potential than FO-RO. A graphical overlapping method suggested in this work can help determine optimal serial configuration and operating conditions of PAFO-RO.

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)

Evaluation of an element-scale plate-type forward osmosis: Effect of structural parameters and operational conditions

This is the first study investigating a plate-type forward osmosis (FO) element in two different operating modes: FO and pressure assisted FO (PAFO). A baseline test was conducted to assess the FO process under different structural parameters and operating conditions. For the PAFO, both the naturally occurring pressure and artificially applied hydraulic pressure in at the feed solution (FS) were considered. FO water flux increased with an increase in the temperature (from 20 to 30°C) and the draw solution (DS) concentration (0.4 to 0.7M). In addition, when the flow rate of the FS increased, the water flux increased and the inlet pressure at the FS side also increased. In the PAFO mode, the water flux increased with an increase in the hydraulic pressure, but the water flux decreased with a 1.5bar hydraulic pressure. The increase in the water flux became smaller as the flow rate difference between the FS and DS increased, which is not the same as the FO mode. This may due to that as the flow rate increases, and the hydraulic pressure is further increased, the central portion of the membrane comes into contact with the spacer at the DS side (bowing phenomenon).

Porous membranes in pressure-assisted forward osmosis: Flux behavior and potential applications

In this work, pressured-assisted forward osmosis (PAFO) was performed using porous membranes to achieve higher fluxes. The effects of additional pressure and membrane orientation on membrane performance were investigated. When ultralow additional pressure (0.04bar) was applied, the water flux at AL-FS orientation (i.e. active layer facing the feed solution) was observed to double. Reverse solute diffusion was also inhibited dramatically at both membrane orientations in PAFO. Filtration tests revealed that porous membranes with ultralow pressure in FO were more applicable than ultrafiltration (UF) because mild condition (i.e., 0.12bar versus 1.25bar) is conducive to preserving microalgae cell integrity.

Effect of intermittent pressure-assisted forward osmosis (I-PAFO) on organic fouling

This study investigated the feasibility of intermittent pressure-assisted forward osmosis (I-PAFO) operation for organic fouling mitigation, using sodium alginate as the model foulant. FO and PAFO were also operated to compare system performances in terms of water flux behavior, flux recovery by physical cleaning, fouling propensity, energy consumption, and membrane area required. Results showed that I-PAFO obtained higher water flux and flux recovery by physical cleaning than PAFO because of its lower fouling tendency. I-PAFO was able to reduce not only the accumulated foulant mass on the membrane surface, but also fouling layer compaction through the intermittent pressurization. Furthermore, it displayed benefits in terms of reducing membrane area required and operating energy compared to PAFO, due to its higher water productivity and sustainability. Therefore, I-PAFO can be a plausible option for saving membrane costs and operating energy when FO operations are concerned particularly in accordance with hybridization with RO (i.e. I-PAFO-RO hybrid process).

Transport of trace organic contaminants (TrOCs) in pressure-assisted forward osmosis (PAFO)

Transport of trace organic contaminants (TrOCs) in pressure-assisted forward osmosis (PAFO)

Effect of Intermittent Pressure-Assisted Forward Osmosis (I-PAFO) Operation on Colloidal Membrane Fouling and Physical Cleaning Efficiency

Effect of Intermittent Pressure-Assisted Forward Osmosis (I-PAFO) Operation on Colloidal Membrane Fouling and Physical Cleaning Efficiency

Application of pressure assisted forward osmosis for water purification and reuse of reverse osmosis concentrate from a water reclamation plant

Abstract The use of forward osmosis (FO) is growing among the researchers for water desalination and wastewater treatment due to use of natural osmotic pressure of draw solute. In this study pressure assisted forward osmosis (PAFO) was used instead of FO to increase the water production rate. In this study a low concentration of draw solution (0.25 M KCl) was applied so that diluted KCl after PAFO operation can directly be used for fertigation. The performance of PAFO was investigated for the treatment of reverse osmosis concentrate (ROC) from a water reclamation plant. The water production in PAFO was increased by 9% and 29% at applied pressure of 2 and 4 bars, respectively, to feed side based on 90 h of experiments. Granular activated carbon (GAC) pretreatment and HCl softening were used to reduce organic fouling and scaling prior to application of PAFO. It reduced total organic carbon (TOC) and total inorganic carbon (TIC) by around 90% and 85%, respectively from untreated ROC. Subsequently, this led to an increase in permeate flux. In addition, GAC pretreatment adsorbed 12 out of 14 organic micropollutants tested from ROC to below detection limit. This application enabled to minimise the ROC volume with a sustainable operation and produced high quality and safe water for discharge or reuse. The draw solution (0.25 M KCl) used in this study was diluted to 0.14 M KCl, which is a suitable concentration (10 kg/m3) for fertigation, due to water transport from feed solution.

Forward osmosis process for supply of fertilizer solutions from seawater using a mixture of draw solutions

Novel desalination approaches are required to provide both drinking and agricultural water as there is ever increasing stress upon precious freshwater resources. It was our hypothesis that a modified Forward Osmosis (FO) process had the potential for production of irrigation water comprising of appropriate concentrations of fertilizers from a seawater feed. Four agents, KNO3, Na2SO4, CaNO3, and MgCl2, plus 35 g/L seawater were used as the draw and feed solutions of the FO process. Net Driving Pressure (NDP) in the FO process was manipulated either by increasing the concentration of draw solution (FO process) or by increasing feed pressure (Pressure Assisted FO (PAFO) process). A series of nanofiltration (NF) and reverse osmosis (RO) membranes were used for the regeneration of draw solution. The results suggested that a PAFO process was more energy efficient than simple forward osmosis, provided the energy relating to the brine flow from the NF/RO membrane for pressurizing the feed solution of PAFO process was used. Furthermore, this study suggested using a mixture of a primary draw solution, MgCl2, and a secondary draw solution, KNO3, for NO3 supply into the irrigation water was preferable. As such, MgCl2 provided the driving force for fresh water extraction while KNO3 was the source of fertilizer in the irrigation water. Results showed that water quality provided by application of a MgCl2+KNO3 draw solution was better than that from KNO3 or Ca(NO3)2. The concentrations of NO3 and SO4 in irrigation water were within recommended levels when the diluted draw solution was regenerated by a dual stage low pressure RO process.

Role of pressure in organic fouling in forward osmosis and reverse osmosis

Fundamental understanding of membrane fouling in osmosis-driven membrane processes is important for further deployment of this emerging technology in desalination and wastewater reuse. In this study, we investigated the role of pressure in organic fouling and reversibility in forward osmosis (FO) and reverse osmosis (RO) using alginate as a model organic foulant. Varying contributions of pressure (i.e., osmotic versus hydraulic) to the overall driving force were realized in forward osmosis (FO), pressure-assisted FO (PFO), and reverse osmosis (RO) experiments, while the same total driving force for water permeation was applied. Confocal laser scanning microscopy was used to examine alginate fouling layer structure in the hydrated state, which informed two key parameters: fouling layer thickness and foulant volume. We observed that the resulting fouling layer became increasingly more compact in the order of FO, PFO, and RO experiments. Fouling layer reversibility followed the same trend, with the highest and lowest reversibility observed for the FO and RO fouling experiments, respectively. Possible mechanisms for fouling layer compaction in RO were discussed, including permeate drag force and foulant compressibility, as opposed to FO where only permeate drag force applies. Our findings suggest that pressure mechanistically alters the membrane fouling layer structure and fouling reversibility, leading to higher fouling reversibility in FO, where the driving force is osmotic pressure, than RO, where the driving force is hydraulic pressure.