A statistics-based forward osmosis membrane characterization method without pressurized reverse osmosis experiment (original) (raw)
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DESALINATION AND WATER TREATMENT, 2018
Generally, forward osmosis (FO) membrane performance is defined based on its intrinsic parameters, namely the water permeability (A), solute permeability (B), and structural parameter (S). This study was conducted to examine the performance of the commercial membrane NF2 in an FO system and to validate and compare the intrinsic value of A, B, and S obtained by single stage-stage and two-stage methods. The NF2 membrane was unable to demonstrate a good configuration for an FO membrane due to its membrane structure. Comparing the two different orientations in the single-stage method, it appears that both orientations display distinct sets of intrinsic values for the same membrane type. A comparison on the two-stage methods between the pressure-retarded osmosis-FO and reverse osmosis (RO)-FO methods reveals a new standard for the two-stage methods where higher fluxes must be produced from the first stage in order to attain an accurate value of S at the second stage. Additionally, the RO-FO methods were found to be not relevant for testing the ability of a membrane for FO application due to the hydraulic pressure involved during the compaction procedure. The two-stage method with proposed new standards can be the ideal testing procedure for the membrane in FO applications. This is because all the intrinsic values can be separately determined considering all the possible concentration polarization that might occur with both orientations compared with the attempts of fitting all possible values in the generated equations, as in single-stage methods.
Osmotically Driven Membrane Processes - Approach, Development and Current Status
Forward osmosis (FO) as an osmotically driven membrane process is severely affected by the concentration polarization phenomenon on both sides of the membrane as well as inside the support layer. Though the effect of internal concentration polarization (ICP) in the porous support on the draw solution side is far more pronounced than that of the external concentration polarization (ECP), still the importance of ECP cannot be neglected. The ECP becomes particularly important when the feed flow rate is enhanced to increase the permeation flux by increasing the agitation and turbulence on the membrane surface. To capture the effect of ECP a suitable value of mass transfer coefficient must be determined. In this chapter, an FO mass transport model that accounts for the presence of both ICP and ECP phenomena is first presented on the basis of solution-diffusion model coupled with diffusion-convection. Then, three methods for the estimation of mass transfer coefficient based on empirical Sherwood (Sh) number correlations, pressure-driven reverse osmosis (RO), and osmosis-driven pressure retarded osmosis (PRO) are proposed. Finally, a methodology for the prediction of water flux through FO membranes using the theoretical model and calculated/measured parameters (hydraulic permeability, salt resistivity of the support layer, and mass transfer coefficient) is presented.
Desalination, 2020
The main reason for the lower water flux, than expected, in the forward osmosis (FO) process, is the internal concentration polarization (DICP). Usually, the structural parameter (S) is used as an indicator of the intensity of DICP. Small S value is desirable for the FO membrane due to the low DICP. However, due to design and construction problems, structural parameter reduction has some drawbacks. In this work, DICP reduction in FO membranes will be investigated using an approach other than structural parameter reduction. Accordingly, during the FO process, the feed solution (FS) valve is opened and closed at a constant period of time (feed valve timing (FVT)). Four types of FO membranes with different S parameters were used. The effects of the implementation of the proposed protocol on the water flux (J w), reverse salt flux (J s), specific reverse solute flux (J s /J w) and effective driving force were investigated. The effects of the S parameter and draw solution (DS) concentration also investigated separately. The results showed that the proposed protocol significantly increased J w. Also, the values of J s /J w decreased with increasing the FVT values and reached the lowest level in the practical recovery time (PRT).
Desalination, 2020
Concentration polarization is one of the inherent problems in forward osmosis membrane process. A quantitative evaluation of concentration polarization is therefore vital to understand its impact on the performance of the forward osmosis. Limited data in the literature exists for the diffusion coefficient of mixed electrolyte or multicomponent solutions, which makes the calculation of mass transfer coefficient and solute resistance to diffusion in forward osmosis complicated. Therefore, an empirical method based on a limited set of well-defined experiments for evaluating and predicting the concentration polarisation, water flux, and reverse solute flux is presented for single and mixed, or multi-ions draw solutions. The proposed method does not rely on the hydrodynamic conditions and flow regime in the system and provides an approach to measure and predict concentration polarisation, water flux, and reverse salt flux when the diffusion coefficient of a feed solution (FS) or draw solution (DS) is challenging to determine. The developed numerical method is two steps method to measure internal and external concentration polarisation using different concentrations of the draw and feed solutions. Experimental work was carried out with a single, and highly soluble sodium chloride (NaCl) DS and a mixture of NaCl and magnesium sulphate (MgSO4) were used as a selected multicomponent DS. The results showed a 95% to 99% agreement with the experimental data.
Journal of Membrane Science, 2013
We present a simple and rapid methodology to characterize the water and solute permeability coefficients (A and B, respectively) and structural parameter (S) of forward osmosis (FO) membranes. The methodology comprises a single FO experiment divided into four stages, each using a different concentration of draw solution. The experimental water and reverse salt fluxes measured in each stage are fitted to the corresponding FO transport equations by performing a least-squares non-linear regression, using A, B, and S as regression parameters. Hand-cast thin-film composite (TFC) FO membranes and commercial TFC FO, TFC reverse osmosis (RO), and cellulose acetate-based asymmetric FO membranes are evaluated following this protocol. We compare the membrane properties obtained with our FO-based methodology with those derived from existing protocols based on an RO experiment followed by an FO experiment. For all membranes, the FO-based protocol gives more accurate predictions of the water and salt fluxes than the existing method. The numerical robustness of the method and the sensitivity of the regression parameters to random errors in the measured quantities are thoroughly analyzed. The assessment shows that confidence in the accuracy of the determined membrane parameters can be enhanced by simultaneously achieving close fitting of the predicted fluxes to experimental measurements (i.e., high R 2 values) and constant water to salt flux ratios in each stage. Additionally, the existing and proposed approaches yield consistently dissimilar results for some of the analyzed membranes, indicating a discrepancy that might be attributed to the different driving forces utilized in RO and in FO that should be further investigated.
Membranes
Water is a necessary resource for life development. Its excessive consumption has a negative impact, generating scarcity problems worldwide. Desalination is an alternative to solve these problems; its objective is to reduce the concentration of total dissolved solids to levels suitable for consumption. The most widely used desalination technology is reverse osmosis, which works by means of semipermeable membranes; however, lack of knowledge or wrong operation cause phenomena such as concentration polarization, which reduces the effective area for mass transfer in the membrane, increasing the energy consumption of the process. The objective of the present study is to evaluate the concentration polarization (β) of the concentration in reverse osmosis membranes by varying the temperature in the feed water (23, 25.5, 28, and 35 °C) for different concentrations (5000 and 10,000 mg L−1) in order to reduce its impact on energy consumption (kWh m−3). The results show that as the temperature...
Study of the prediction model of water flux through a forward osmosis membrane
DESALINATION AND WATER TREATMENT, 2021
This work aims at evaluating the accuracy of Tiraferri's model introduced in 2013 for predicting water flux through the forward osmosis (FO) membrane. To this end, a database of FO membranes with their intrinsic parameters and experimental water fluxes was thus constituted. The model was solved numerically in Python Software, first by considering the contribution of external concentration polarization (ECP), and by neglecting it. Using the pressure retarded osmosis mode model, the mass transfer coefficient was adjusted to fit the experimental data to the transport equation. The predicted water fluxes are mostly in agreement with the experimental data, with a resulting mean absolute error (MAE) of 9.18%. This study also shows that the error caused by ECP is less than 1% when deionized water is used as feed solution in FO mode. Because of the reverse salt flux, the ECP was found higher when membranes with high water or salt permeability are tested. The error in van't Hoff prediction, from which the model is based, was found to be low when the draw solution has a concentration in the range of 1 to 2.3 M.
DESALINATION AND WATER TREATMENT, 2018
A chemical cleaning process is widely used to restore flux decline and solute rejection in membrane-based water treatment processes such as reverse osmosis (RO) process. In this study, the protocols for the chemical cleaning conditions in the RO process were optimized using a response surface methodology (RSM) for minimizing the experiment time and forward osmosis testing setup , which can be operated with low or no hydraulic pressure, for reducing the usage of high hydraulic pressure pump. Fouled membranes were cleaned in accordance with the statistically designed conditions of various acid and alkaline agents with concentration, pH, and temperature as variables. Based on response surface plots, the chemical agent concentration was found to be the most influential factor to the membrane permeability. The optimum cleaning conditions obtained from RSM were 3% of the acid agent concentration at pH of 2.2 followed by 3% of the alkaline agent concentration at pH lower than 13. At these optimum conditions, the water flux was recovered about 86.1% with the salt rejection of 83.6%, compared with those of virgin membrane in RO process. Furthermore, this method could provide better understanding of the relationship among chemical cleaning agent concentration, pH, and temperature.
DESALINATION AND WATER TREATMENT, 2017
Forward osmosis (FO) is a membrane process that makes use of the osmosis phenomenon for the transport of water from a feed solution to a draw solution across a highly selective membrane under a driving force provided by the osmotic pressure difference between the two solutions. Based on energy consumption, this technology has got an edge over others. However, limited advancement on theoretical modeling for prediction of performance, lack of an ideal FO draw solution, concentration polarization and lack of economic feasibility have made this technology to proceed through further research with an objective of commercialization from 1970 to 2016. Although the technology has many potential applications, like wastewater treatment, membrane bioreactor, oil and gas, pharmaceutical, food and beverage etc., it still faces considerable limitations, including concentration polarization, membrane development and characterization, reverse solute diffusion, development of draw solution and their recovery. In order to address these issues more research is required. This paper presents a state-of-art review on FO technology covering types of membrane, draw solute, their characteristics, concentration polarization, identification of parameters, dynamic modeling of separation, novel membrane and hybrid systems from 103 literatures.