Draw Solution Flow Rate Research Articles

Performance evaluation of a thermoresponsive polyelectrolyte draw solution in a pilot scale forward osmosis seawater desalination system

The current study assesses the technical feasibility of using a thermoresponsive polyelectrolyte draw solution (DS) in a Forward Osmosis (FO) desalination pilot scale system of 10 m3/day capacity. The FO system utilized a commercial spiral wound hollow fiber FO membrane and ethylene oxide-propylene oxide copolymer as DS. This study evaluated the effect of DS flow rate and feed solution flow rates on the net water recovery and product water flow rates of the system. The osmotic pressure distribution of polyelectrolyte DS at different sections of the HF module was greatly influenced by DS flow rate. The study revealed that the DS had great potential to generate the high osmotic pressure (Δπ) difference in the various compartments of the HF module. The reliability of the FO pilot plant was proved over a long run without any severe FO membrane fouling with total dissolved solids of product water at 143 ppm and water recovery of 30%. The selected DS showed its potentiality towards the installation of commercial-scale FO desalination plant by witnessing its low viscosity and easy phase separation at a moderately lower temperature of 85 °C in the coalesce DS regeneration system.

Synthesis of polybenzimidazole (PBI) forward osmosis (FO) membrane and computational fluid dynamics (CFD) modeling of concentration gradient across membrane surface

This research study aimed to synthesize polybenzimidazole (PBI) FO flat sheet membranes for seawater desalination in high temperature and salinity regions like the UAE. The fabrication conditions that were considered to improve membrane performance included casting thickness, oven temperature and duration. The impact of draw and feed solution flow rates, draw solution type and concentration was also investigated. The ideal fabrication conditions for 15 wt% PBI FO membranes were found to be 150 μm casting thickness, heat treatment for 1.5 min at 165 °C and an immersion duration of 10 min in coagulation bath at 23 °C. Performance results showed that the optimal membrane achieved a water flux and salt rejection of 4.2 LMH and 97.4%, respectively with 2 M MgCl2 draw solution, which increased 21.3 LMH and 98.8%, respectively when the draw solution was allowed to flow in the top compartment of the membrane cell (orientation B). Additionally, computational fluid dynamics (CFD) modeling was used to study the impact of concentration gradient across membrane film on water flux and salt rejection at different FO cell orientation when operated at low cross-flow velocities. CFD modeling results demonstrated that solution density, gravity and diffusion rate affected FO performance at low cross-flow velocity.

Dilution of seawater using dewatered construction water in a hybrid forward osmosis system

Abstract In this study, dewatered construction water was used for the first time as the feed solution in a combined pretreatment-forward osmosis process to dilute seawater (i.e. draw solution) for further desalination. It was found that at a feed solution and a draw solution flow rate of 2.2 L min−1 gave the optimum membrane flux with minimal fouling effects. The addition of a spacer in the membrane feed side was effective at low flow rates (0.8 and 1.5 L min−1). The feed solution was then pretreated using two methods: settling and multimedia filtration and used in the forward osmosis unit at a low flow rate of 0.8 L min−1 using a spacer at the feed side. Results revealed a significant increase in the forward osmosis membrane flux by 64.3% when multimedia filtration was carried out with a flux reduction of 7.7%. While the settling method achieved only 13.5% increase in the permeate flux and 12.5% flux reduction. The multimedia filtration process removed most of the particles that would cause fouling which resulted in an elevated and more consistent membrane flux. Results also showed that the water flux was 1.3 times higher when the membrane's active layer was facing the draw solution than when it was facing the feed solution. Cost analysis showed that forward osmosis treatment of dewatered construction water was 7.88 $.day−1 and it was slightly cheaper when the forward osmosis operates in the pressure retarded osmosis mode.

Experimental study and modeling of forward osmosis process for activated sludge concentration by using residual brine from a stuffed olive factory as draw solution

In the present study, effect of external and internal concentration polarization (ECP and ICP), and reversible fouling on water flux behavior was evaluated for an activated sludge concentration process. A solution of activated sludge from the biological treatment unit of a wastewater treatment plant was used as a feed solution (FS), with an initial total suspended solids (TSS) concentration of 6198 mg/L. Residual brine from a stuffed olive factory was used as a draw solution (DS) because of its osmotic potential (equivalent to 1.2 M NaCl). This resulted in an increase in the initial FS concentration to around 16,850 mg/L. The experimental tests were carried out in a pilot plant with a flat FO membrane cell of 34 cm2, and FS and DS flow rates of 2 L min−1 and 0.5 L min−1, respectively, at 20 ±0.3 °C. An active layer facing the FS orientation was selected because of the high TSS concentration of the feed. Permeate flux showed initial values around 13.5 ± 0.5 L m−2/h for the first two hours of operation, but this gradually decreased to 5.3 ± 0.5 L m−2/h after 24 h. By modeling permeate flux performance, the role that the feed and draw concentrations, membrane orientation, and membrane properties play in water flux were elucidated and linked to the prevalence of external and internal concentration polarization. Internal concentration polarization and fouling on the active layer were found to play a significant role in the reduction in the driving force for the chosen system conditions.

Concentrating molasses distillery wastewater using biomimetic forward osmosis (FO) membranes

Treatment of sugarcane molasses distillery wastewater is challenging due to the presence of complex phenolic compounds (melanoidins and polyphenols) having antioxidant properties. Due to zero liquid discharge regulations, Indian distilleries continue to explore effective treatment options. This work examines the concentration of distillery wastewater by forward osmosis (FO) using aquaporin biomimetic membranes and magnesium chloride hexahydrate (MgCl2.6H2O) as draw solution. The operational parameters viz. feed solution and draw solution flow rate and draw solution concentration were optimized using 10% v/v melanoidins model feed solution. This was followed by trials with distillery wastewater. Under the conditions of this work, feed and draw flow rates of 1 L/min and draw solution concentration of 2M MgCl2.6H2O for melanoidins model solution and 3M MgCl2.6H2O for distillery wastewater were optimal for maximum rejection. Rejection of 90% melanoidins, 96% antioxidant activity and 84% COD was obtained with melanoidins model feed, with a corresponding water flux of 6.3 L/m2h. With as-received distillery wastewater, the rejection was similar (85–90%) to the melanoidins solution, but the water flux was lower (2.8 L/m2h). Water recovery from distillery wastewater over 24 h study period was higher with FO (70%) than reported for RO (35–45%). Repeated use of the FO membrane over five consecutive 24 h cycles with fresh feed and draw solutions and periodic cleaning showed consistent average water flux and rejection of the feed constituents.

Systematic analysis and optimization of power generation in pressure retarded osmosis: Effect of multistage design

This work presents a systematic method for analysis and optimization of specific energy production (SEP) of pressure retarded osmosis (PRO) systems employing single‐stage configuration as well as multistage design with interstage hydro‐turbines. It is shown that the SEP normalized by the draw solution feed osmotic pressure increases with the number of stages as well as a dimensionless parameter . As compared to the single‐stage PRO, the multistage arrangement not only increases flux and volume gain, but also allows a stage‐dependent, progressively decreasing hydraulic pressure, both of which contribute to enhanced SEP and power density. At the thermodynamic limit where γtot goes to infinity, the theoretical maximum SEP by an N‐stage PRO system is , where qtot is the ratio of the draw solution flow rate at the outlet to the inlet on the system level. For single‐stage PRO, it is no more than π0. For infinite number of stages, the theoretical limit becomes . SEP under realistic conditions and practical constraints on multistage design are discussed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 144–152, 2018

Combination and performance of forward osmosis and membrane distillation (FO-MD) for treatment of high salinity landfill leachate

Abstract Forward osmosis (FO) was combined with membrane distillation (MD) to treat high salinity hazardous waste landfill leachate. Response surface methodology (RSM) was used to optimize the operating conditions of the FO process by maximizing water flux and removal efficiency of pollutants and minimizing the salt reverse flux. Flow rate of FS (feed solution), flow rate of DS (draw solution) and the concentration of DS were selected as independent variables for incorporation in the Box-Behnken design. Results showed that optimal FS flow rate, DS flow rate and DS concentration for FO stage were 0.87 L/min, 0.31 L/min and 4.82 M, respectively. The optimal temperatures of inlet solution in MD stage were 72.5 ± 0.5 °C and 62.5 ± 0.5 °C when salt concentrations in FS were 25,000 mg/L and 60,000 mg/L (calculated as NaCl). Salt rejection rates were higher than 96% while rejection rates of TOC and TN were higher than 98%. NH 4 + -N, Hg, As and Sb were completely removed. The results proved optimized FO-MD combined system was a suitable process to treat high salinity hazardous wastewater.

Comparative Study for Organic and Inorganic Draw Solutions in Forward Osmosis

The present work aims to study forward osmosis process using different kinds of draw solutions and membranes. Three types of draw solutions (sodium chloride, sodium formate, and sodium acetate) were used in forward osmosis process to evaluate their effectiveness with respect to water flux and reverse salt flux. Experiments conducted in a laboratory-scale forward osmosis (FO) unit in cross flow flat sheet membrane cell. Three types of membranes (Thin film composite (TFC), Cellulose acetate (CA), and Cellulose triacetate (CTA)) were used to determine the water flux under osmotic pressure as a driving force. The effect of temperature, draw solution concentration, feed and draw solution flow rate, and membrane types, were studied with respect to water flux. The results showed an increase in water flux with increasing feed temperature and draw solution concentrations In addition, the flux increased with increasing feed flow rate while the flux was inversely proportional with the draw solution flow rate. The results showed that reverse osmosis membranes (TFC and CA) are not suitable for using in FO process due to the relatively obtained low water flux when compared with the flux obtained by forward osmosis membrane (CTA). NaCl draw solution gave higher water flux than other draw solutions and at the same time, revealed higher reverse salt flux.

Performance of a Novel Fertilizer-Drawn Forward Osmosis Aerobic Membrane Bioreactor (FDFO-MBR): Mitigating Salinity Build-Up by Integrating Microfiltration

In this paper, three different fertilizer draw solutions were tested in a novel forward osmosis-microfiltration aerobic membrane bioreactor (MF-FDFO-MBR) hybrid system and their performance were evaluated in terms of water flux and reverse salt diffusion. Results were also compared with a standard solution. Results showed that ammonium sulfate is the most suitable fertilizer for this hybrid system since it has a relatively high water flux (6.85 LMH) with a comparatively low reverse salt flux (3.02 gMH). The performance of the process was also studied by investigating different process parameters: draw solution concentration, FO draw solution flow rate and MF imposed flux. It was found that the optimal conditions for this hybrid system were: draw solution concentration of 1 M, FO draw solution flow rate of 200 mL/min and MF imposed flux of 10 LMH. The salt accumulation increased from 834 to 5400 μS/cm during the first four weeks but after integrating MF, the salinity dropped significantly from 5400 to 1100 μS/cm suggesting that MF is efficient in mitigating the salinity build up inside the reactor. This study demonstrated that the integration of the MF membrane could effectively control the salinity and enhance the stable FO flux in the OMBR.

A closed-loop forward osmosis-nanofiltration hybrid system: Understanding process implications through full-scale simulation

This study presents simulation of a closed-loop forward osmosis (FO)-nanofiltration (NF) hybrid system using fertiliser draw solution (DS) based on thermodynamic mass balance in a full-scale system neglecting the non-idealities such as finite membrane area that may exist in a real process. The simulation shows that the DS input parameters such as initial concentrations and its flow rates cannot be arbitrarily selected for a plant with defined volume output. For a fixed FO-NF plant capacity and feed concentration, the required initial DS flow rate varies inversely with the initial DS concentration or vice-versa. The net DS mass flow rate, a parameter constant for a fixed plant capacity but that increases linearly with the plant capacity and feed concentration, is the most important operational parameter of a closed-loop system. Increasing either of them or both increases the mass flow rate to the system directly affecting the final concentration of the diluted DS with direct energy implications to the NF process. Besides, the initial DS concentration and flow rates are also limited by the optimum recovery rates at which NF process can be operated which otherwise also have direct implications to the NF energy. This simulation also presents quantitative analysis of the reverse diffusion of fertiliser nutrients towards feed brine and the gradual accumulation of feed solutes within the closed system.

Modeling and optimization of a solar forward osmosis pilot plant by response surface methodology

Forward osmosis (FO) is a water treatment/separation technology of emerging interest. Due to its complex nature involving various operating parameters, modeling of this separation process is challenging. A solar thermal and photovoltaic-powered FO pilot plant has been optimized by means of a statistical experimental design and response surface methodology. Predictive models were developed for simulation and optimization of different responses such as the water permeate flux, the reverse solute permeate flux and the FO specific performance index that includes the water and reverse solute permeate fluxes together with the energy consumption. The considered input variables of the FO pilot plant were the feed flow rate, the permeate flow rate and the temperature. The developed response models have been tested using the analysis of variance. A Monte Carlo Simulation method has been conducted to determine the optimum operating conditions of the FO pilot plant. The obtained optimum parameters were confirmed experimentally. Regeneration of the draw solution can be performed by means of an optimized solar powered reverse osmosis (RO) pilot plant with an optimum FO specific performance index ranging from 25.79 to 0.62L/gkWh achieved under the FO optimal conditions, 0.83L/min feed flow rate, 0.31L/min draw solution flow rate and 32.65°C temperature. The FO energy consumption is only 14.1% the total energy consumption of the FO/RO hybrid system.

Combined influence of temperature and flow rate of feeds on the performance of forward osmosis

The effect of the membrane orientation, feeds flow rate, feeds temperature, and combining effect of both temperature and flow rate on the membrane flux was investigated in order to enhance the performance of forward osmosis (FO) process. Results from experimental work demonstrated that the concentrative internal concentration polarization (CICP) could be mitigated by increasing the feed solution flow rate and using a spacer. On contrary, the severity of dilutive internal concentration polarization (DICP) phenomena was aggravated by increasing the draw solution flow rate. It was also found that when increasing the draw solution (DS) temperature from 20°C to 26°C the flux increased linearly and then started decreasing when temperature increased over 26°C due to the development of a temperature gradient. The experimental results also showed that the membrane flux increased by 93.3% due to temperature increase from 20 to 26°C and the flow rate from 1.2 to 3.2L/min using a 0.5M NaCl solution as the draw solution and distilled water as the feed solution (FS).

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...

Water recovery and solute rejection in forward osmosis modules: Modeling and bench-scale experiments

Forward osmosis (FO) processes have potential applications in the treatment of complex and highly impaired sources of water. In this study, the performance of a FO module is evaluated in terms of its ability to recover water from a feed solution and its ability to minimize solute leakage. These performance metrics are expressed in terms of the recovery rate and separation factors, respectively. An analytical model that quantifies the effects of membrane properties (e.g., selectivity) and operating conditions (e.g., the ratio of the draw solution flow rate to the feed solution flow rate) on the recovery rate and separation factors is developed. Numerical solutions of the non-linear governing equations and bench-scale experiments with ionic and non-ionic solutes (i.e., NaCl, KCl, MgCl2, CaCl2, and urea) were used to test the validity of the derived model. Both the numerical solutions and experimental results corroborated the ability of the derived model to predict the performance of a FO module. Electrostatic and other multicomponent interactions, which were not included in the model, were observed in some experiments resulting in poor agreement with the predicted performance. Analysis of the model establishes membrane selectivity and draw solute concentration as the dominant factors that determine the extent of water recovery and solute rejection in a FO module. Further analysis of the model suggests that current membranes could achieve acceptable levels of solute rejection for desalination applications (> 99.3%) at relatively high draw solute concentrations (2.5M draw solution for a 0.6M feed solution at 50% recovery), but more selective membranes are necessary to reduce the draw solute concentration closer to the thermodynamic limit established by osmotic equilibrium. Finally, a simple heuristic for selecting the flow ratio based on the entering concentrations of the feed solution and draw solution and the desired recovery rate is identified.

Effect of the feed and draw solution temperatures on PRO performance: Theoretical and experimental study

In this study, a model for the water flux and the salt flux for a flat sheet membrane in pressure retarded osmosis (PRO) is developed and experimentally validated. The model focuses in the effects of operating conditions (feed and draw solution concentrations, flow rate, and temperature) on PRO performance. The validation results show a good predictability of the models under different operating conditions. An improvement of the PRO performance was shown by increasing the bulk solution temperature and the flow rate. The study of the effect of these temperatures on the performance of the PRO revealed that the feed solution temperature has a stronger impact on the membrane parameter of the PRO performance comparing to the draw water temperature. However, the increase of the water flux which resulted from the increase of the feed solution temperature is accompanied by a high salt diffusion inducing a severe internal concentration polarization (ICP). The strong relationship between the water flux and the salt flux is shown to be due to the intrinsic tradeoff between permeability and selectivity.

Numerical study of a hybrid multi-stage vacuum membrane distillation and pressure-retarded osmosis system

In this study, we introduce a hybrid system that integrates a multi-stage vacuum membrane distillation (MVMD) with pressure-retarded osmosis (PRO). The MVMD system employs a recycling flow scheme (MVDM-R) for the continuous production of both distillate water and highly concentrated brine. The concentrated brine that is produced from the MVMD-R system is then used as a draw solution for power generation in the PRO system. We theoretically assessed the distillate and power production of the MVMD-R-PRO system with respect to inlet feed flow rate and recycling flow ratio in the MVMD-R system. When the inlet feed flow rate is constant, the production of distilled water increases slightly, with a decrease in the recycling flow. The maximum possible brine concentration from the MVMD-R system is 1.9M NaCl at an inlet feed flow rate of 3kg/min and a 90% recycling flow. A maximum power density of 9.7W/m2 is achieved when river water is used as a feed solution in the PRO system at feed and draw solution flow rates of 0.5kg/min and a constant hydraulic pressure difference.

Dual stage PRO process: impact of the membrane materials of the process performance

A dual stage pressure retarded osmosis (PRO) process was investigated for power generation using different types of membranes. Polyamide (PA) and cellulose triacetate (CTA) membranes were used in the first and second stage of the PRO process to improve the process performance due to the high water permeability of PA membranes. A comparison between dual stage PA–CTA and CTA–CTA membrane systems were carried out using seawater as a draw solution, while fresh water and wastewater effluent were the feed solution in the first and second stage of the process. The impact of draw solution flow rate on the process performance was evaluated. The performance of first and second stage of the PRO process increased by 11.5 and 28.6%, respectively, when the draw solution flow rate increased by a factor of 2.5. In return, there was a negligible increase in the total specific power consumption of the PRO process. In general, power consumption of the dual stage PRO process was as low as 0.3 kWh/m3. Furthermore, the results showed that the performance of the dual stage PRO process increased with increasing seawater salinity from 32 to 50 g/L due to the higher net driving pressure across the membrane. Finally, power generation in the PA–CTA system was up to 33% higher than that in the CTA–CTA system.

Analysis and optimization of pressure retarded osmosis for power generation

Model‐based analysis and optimization of pressure retarded osmosis (PRO) for power generation is focused. The effects of membrane properties (hydraulic permeability and mass‐transfer characteristics), design conditions (inlet osmotic pressures, inlet flows, and membrane area) and operating condition (applied pressure) on power density and efficiency are systematically investigated. A dimensionless design parameter , originally developed in analysis and optimization of reverse osmosis, is used to quantify the effect of dilution in draw solution (DS) as water permeates through membrane. An optimization method is developed to maximize PRO performance. It is shown that dilution and concentration polarization significantly reduce the maximum power density, and the optimal shifts away from . Moreover, power density and efficiency follow opposite trends when varying process conditions including DS flow rate and membrane area. Enhancing membrane properties is crucial to improve the economic feasibility of PRO. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1233–1241, 2015

Dual-stage forward osmosis/pressure retarded osmosis process for hypersaline solutions and fracking wastewater treatment

Hypersaline solution with high TDS is not suitable for direct treatment by the conventional membrane and thermal processes. The current study proposes a dual-stage FO/PRO process for hypersaline solution treatment and power generation. The treatment process reduces the concentration of saline wastewater and hence renders it suitable for disposal directly to sea or treatment by the conventional membrane and thermal processes. The draw and feed solutions in the FO process were the hypersaline solutions and wastewater effluent, respectively. Five concentrations were evaluated for the process treatment with different concentrations ranging from 53g/L to 157g/L. The performance of FO membrane was estimated using pre-developed computer software. The results showed that a higher power can be generated from the PRO-FO system than from the FO-PRO system without compromising the concentration of hypersaline solution after dilution. The study also showed that although increasing the flow rate of draw solution resulted in an increase in the permeate flow rate, it caused a reduction in the dilution of draw solution. On the other hand, the study showed a negligible improvement in the performance of FO membrane upon increasing the feed solution flow rate. Finally, the simulation results showed that the concentration of diluted draw solution was suitable for the conventional membrane and thermal treatments or discharge to seawater after the dual-stage FO membrane treatment.

Evaluation of FO-RO and PRO-RO designs for power generation and seawater desalination using impaired water feeds

PRO and FO coupling with an RO membrane process is proposed to reduce the cost of seawater desalination and the potential for power generation. Three conceptual design configurations, PRO-RO, FO-RO and RO-PRO were evaluated here using standard seawater concentration and impaired water as the draw and the feed solutions respectively. The PRO-RO and RO-PRO designs were evaluated for power generation and seawater desalination while the FO-RO design was proposed for seawater desalination only. The impact of the draw and feed solutions' flow rate and the impaired water TDS on the performance of each design was estimated using pre-developed software. The simulation results showed that the performance of all designs was more sensitive to the increase in the flow rate of draw solution than to the flow rate of feed solution. Furthermore, all designs showed a decrease in membrane flux and recovery rate with increasing the TDS of feed water from 0.2g/L to 10g/L as a result of decreasing the net driving force across the membrane and the concentration polarization phenomenon. The FO-RO design produced the lowest RO permeate concentration followed by the PRO-RO and RO-PRO designs respectively. In terms of power generation, the RO-PRO design was more efficient than the PRO-RO design. The FO-RO design exhibited the lowest desalination power consumption followed by the PRO-RO and RO-PRO designs respectively. At 10g/L feed concentration, the net power consumption in the FO-RO was 9.4% less than that in the PRO-RO which was in turn 5.3% less than that in the RO-PRO design. The estimated cost of the FO/PRO module in the PRO-RO design was 2.2 and 4.3 times higher than that in the FO-RO and RO-PRO designs respectively.