Pollutants removal from wastewaters through membrane distillation

doi:10.1016/j.desal.2005.03.041

Desalination

Volume 183, Issues 1–3, 1 November 2005, Pages 383-394

Presented at the Conference on Desalination and the Environment, Santa Margherita, Italy, 22–26 May 2005. European Desalination Society.

https://doi.org/10.1016/j.desal.2005.03.041 Get rights and content

Abstract

The Sweeping Gas Membrane Distillation process is considered for the treatment of wastewaters containing volatile organic compounds such as acetone and ethanol. The separation technique is based on the use of microporous hydrophobic membranes under conditions of non wettability, in which the membrane separates an aqueous phase from a stripping gas.

A wide experimental investigation is performed to study the role of temperature, composition and flow rate of the liquid phase and the influence of the sweeping gas flow rate. Performances of flat PTFE membranes are studied in the case in which dry nitrogen is used as stripping agent. Liquid feed flow rate as well as nitrogen flow rate are identified as the major design quantities since they greatly affect the separation efficiency.

A simplified mathematical model is developed to describe multicomponent mass transfer in the gas phases, in which a pseudo-binary diffusion approach is assumed; molecular diffusion is considered as the prevailing transport mechanism through the membrane. The results obtained are compared with the experiments and the validity range of the model is defined.

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Wastewater treatment is essential as freshwater becomes scarce due to increasing industrialization. However, the current centralized wastewater treatment technologies are suitable for large-scale applications. There is a pressing need to develop small-scale decentralized wastewater treatment techniques. Towards this goal, a new sweeping gas membrane distillation system (SGMD) integrated with a multistage bubble column dehumidifier (BCD) was designed, built and tested to treat metalworking fluid (MWF)-contaminated wastewater. The performance of the SGMD-BCD system was first optimized using deionized water experiments. The results showed that feed water temperature significantly affected permeate flux, while air and feed water mass flow rates of 10kg/hr and 90kg/hr were identified as optimum since permeate flux and gain output ratio were insignificant above these flow rates. The simulation results of the developed system-scale mathematical model revealed that multi-staging is a more preferable option for improving effectiveness compared to increasing the condensing area in a single-stage BCD. Additionally, in long-term experiments, about 35.5% and 47.7% drops in permeate flux were observed when the MWF concentration in wastewater increased from 5 to 25 wt% at feed water temperatures of 70°C and 80°C, respectively.
Photothermal Sweeping Gas Membrane Distillation and Reverse Electrodialysis for light-to-heat-to-power conversion
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Water and energy are two intimately interconnected issues of strategic relevance for a sustainable industrial development. Herein, we integrated light-harvesting/self-heating membranes and salinity gradient technology with the aim to implement the innovative concept of light-to-heat-to-power conversion.
Novel photothermal membranes, prepared by immobilizing silver nanoparticles (AgNPs) on the top layer of microporous polyvinylidene fluoride (PVDF) matrix, were tested – for the first time – in a Sweep Gas Membrane Distillation (SGMD) unit applied to the desalination of synthetic seawater solution (0.5M NaCl). As a result of the ability of noble metal nanofillers to act as localized thermoplasmonic nano-heaters at membrane-feed interface for efficient water evaporation, an increase of transmembrane flux under UV radiation by about 10-fold with respect to unloaded PVDF membrane was observed.
The SGMD retentate, consisting in hypersaline brine (progressively concentrated up to 4M NaCl and rejected at about 40°C) was fed to a Reverse Electrodialysis unit with the aim to harvest electrochemical energy. The maximum power density, measured for a retentate concentration increasing from 1M to 4M, raised from 0.13 to 0.9 W/m²_MP (MP: RED membrane pair). Overall, the proposed integrated membrane system allowed to extract about 10% of the energy not employed for water evaporation.
Sweeping gas membrane distillation (SGMD) for wastewater treatment, concentration, and desalination: A comprehensive review
2020, Chemical Engineering and Processing - Process Intensification
Citation Excerpt :
The same study also went on to show that their module design did not promote enough turbulence in the feed channel, which did not reduce the effects of concentration polarization. Similar studies in industrial settings have also targeted the separation of volatile organic compounds from aqueous solutions [18,22,25,32] and the breaking of azeotropic mixtures [20]. In these cases, where the concentration of a solute(s) in the permeate is targeted, the selectivity coefficient (β) is commonly used.
This study provides a state-of-the-art review of the advantages and disadvantages of Sweeping Gas Membrane Distillation (SGMD), particularly in the separation and purification processes. The origin of SGMD and comparison of SGMD to other membrane distillation methods are provided. Results from experimental and modeling studies of SGMD from 2000 to 2020 are tabulated and discussed. The mechanisms of heat and mass transport, as well as the modeling and simulation studies, are systematically reviewed. The impact of major operating parameters (feed temperature, feed flow rate, gas temperature, and gas flow rate) and implemented membranes on SGMD performance are discussed and highlighted. Potential applications and areas where SGMD could excel are pointed out. Finally, future research opportunities in the SGMD are identified.
A general predictive model for sweeping gas membrane distillation
2018, Desalination
Among the configurations of membrane distillation processes, sweeping gas membrane distillation (SGMD) remains one of the less studied. In spite of an increasing number of publications, generally the modeling of SGMD has been carried out by fitting heat and mass transfer coefficients and with the use of empirical correlations. In this work, a general predictive model based on computational fluid dynamics (CFD) is presented. This model allows simulating hollow fiber and flat sheet configurations under wide range of process conditions; with a minimum number of input data and without requiring empirical parameters or laboratory experiments. For this purpose, the momentum, mass and heat balances of the process are described by partial differential equations, algebraic and ordinary differential equations. The model has been validated with experimental results available in the literature. Indeed, the influence of operating conditions and membrane geometric characteristics on the process performance was investigated. The conducted studies prove that the proposed model would be potentially applied for the optimization of process conditions, design of membrane modules as well as for the further cost estimation of the process.
Membrane-assisted crystallization: Membrane characterization, modelling and experiments
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Citation Excerpt :
With the help of this model the fluid and the total heat transfer coefficients, hfluid and htot, are calculated (Khayet et al., 2000b; Alkhudhiri et al., 2012). Combined Knudsen/ordinary molecular diffusion can be introduced as Dmem (m2/s) with the help of resistance-in-series model (Khayet et al., 2003, 2000a, 2000b; Schofield et al., 1987; Khayet et al., 2002; Lawson and Lloyd, 1997; Phattaranawik et al., 2003; Rivier et al., 2002; Zheng et al., 2005; Karanikola et al., 2015; Martı́nez-Dı́ez and Vazquez-Gonzalez, 1999; El-Bourawi et al., 2006; Basini et al., 1987; Mahmud et al., 2000; Boi et al., 2005; Sherwood and Pigford, 1952; El Diasty et al., 1993; Zhang and Huang, 2011). Nusselt number, Nu, for both the shell and the lumen side can be calculated using the Chilton-Colburn analogy to couple mass and heat transfer in gas liquid systems (Zhang, 2011).
A hollow fiber membrane module was assessed for its potential in assisting crystallization processes. The membrane module was characterized in the sweeping gas membrane distillation configuration considering various solution and sweeping gas flow rates, temperatures and solution concentrations. A model, coupling mass and heat transfer, was developed to predict the membrane flux. The effect of the process conditions on the membrane flux was experimentally determined and the results were used to validate the model. Feed temperature and air flow rate were found to have a significant effect on the membrane flux. Having found the optimal process conditions for membrane distillation process, batch seeded crystallization experiment were performed to confirm the potential of membrane distillation in the generation of adequate rate and level of supersaturation. Since the desired supersaturation level could be maintained in the crystallizer while seeds were growing, it is confirmed that membrane distillation can be an efficient alternative to conventional supersaturation generation processes. Finally, comparing the modelling results with experiments confirms the acceptable accuracy and predictability capability of the developed model.
Experimental study of hollow fiber AGMD modules with energy recovery for high saline water desalination
2014, Desalination
Citation Excerpt :
Compared with the conventional desalination technologies such as multi-stage flash distillation (MSF), multi-effect distillation (MED) and reverse osmosis (RO), the MD process has several technical advantages such as low operating temperature and pressure, high salt rejection (around 100%), no other chemicals required, large evaporation area, avoiding corrosion problem and no salt concentration limit [7,8]. MD can be developed for seawater and brackish water desalination [9–13], waste water treatment and pure water purification [14–17]. The MD process has been widely studied in laboratory-scale and made a great achievement especially in the mass and heat transfer processes [4].
Hollow fiber AGMD modules with energy recovery for high saline water desalination were successfully developed by using parallel hollow fiber membranes and heat-exchange hollow fibers. Latent heat of distillate water vapor was recovered by heat-exchange hollow fibers directly to heat the cold feed within the AGMD module. Water permeate flux (J_D) and gained-output ratio (GOR) parameters were used to characterize the operation performance of the AGMD process. GOR obtained in the AGMD process was higher than that obtained in traditional membrane distillation processes. The maximum value of J_D and GOR could reach 6.98 kg/m²h and 6.44 respectively. The effects of various operation parameters including feed temperatures and feed flow rate on the performance of the AGMD process had been investigated. The effects of various membrane module parameters such as membrane porosity (ε), membrane pore size (d_r), the rate of hollow fibers and membranes (N_d/N_m), the thermal conductivity coefficient of heat-exchange hollow fibers (k_d), the thickness of hollow fibers (d_d) and the air gap width (d_a) were experimentally studied. The high saline water of 70 g/L was concentrated to about 308 g/L in the deep-concentration experiment. In the long-term stability test lasting for 45 days, the maximum value of the electrical conductivity of the distillate was always less than 200 μS/cm.

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Pollutants removal from wastewaters through membrane distillation

Abstract

Desalination

J. Membr. Sci.

J. Membr. Sci.

Desalination

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.

J. Membr. Sci.