Air Gap Membrane Distillation Process Research Articles

Experimental Study on the Removal of Toluene from Water by PTFE Hydrophobic Microporous Membrane Using Air Gap Membrane Distillation Process

Toluene is used for various purposes such as a cleansing agent, paint thinner, lacquers, printing, and leather tanning process. However, it has an adverse effect on human bodies, such as skin irritation, leukemia, respiratory issues, mutagenicity, etc, when the chemical gets mixed in drinking and rainwater by the above routes. Therefore, there is a threat to the environment and society because of the presence of toluene in water bodies through industrial effluent. Henceforth, in this study, toluene is separated from water using the air gap membrane distillation (AGMD) process. The hydrophobic microporous poly-tetra- fluoro-ethylene has been employed for this purpose. Primarily, this work focussed on the study of operating parameters such as feed solution temperature and coolant temperature on the AGMD performance namely permeate flux and toluene selectivity. It was observed that the permeate flux increased exponentially from 2.07 kg/m2h to 9.23 kg/m2h, and 0.94 kg/m2h to 3.53 kg/m2h. However, it was found that the permeate flux decreased from 9.48 kg/m2h to 8.12 kg/m2h, and 3.78 kg/m2h to 2.42 kg/m2h on increasing the coolant temperature from 5°C to 25°C at 3 mm and 11 mm air gap, respectively. The membrane selectivity was found to be less than 1, which signifies the efficient toluene-water separation. In order to study the membrane performance in the long run, the permeate flux was estimated continuously till 60 h wherein the estimated flux was found to be almost constant. The membrane morphology before and after the 60 h experimental run was analysed using capture FE-SEM micrographs. The toluene concentration was estimated using a spectrophotometer at a wavelength of 264 nm.

Performance assessment and optimization of adsorption-assisted air gap membrane distillation process for remediation of chromium-contaminated groundwater

Chromium contamination in groundwater is becoming a significant concern due to its potential contribution to the global cancer burden. Membrane distillation (MD) is a promising method known for producing high-quality water, yet issues namely temperature and concentration polarizations should be addressed. To overcome these issues, adsorption (ADS) is proposed to reduce Chromium concentration in the concentrated feed and enhance water production and resource recovery. This study assesses the performance optimization considered parameter effects of the process individually and subsequently executes it into a combined process. Slow sand filtration (SSF) is performed to eliminate particles and thus mitigate fouling. A novel Fe3O4@C-SiO2 is introduced in the ADS process. The technical and economic performances of single MD, hybrid systems (ADS-MD and SSF-MD), and an integrated SSF-ADS-MD system are compared. The results showed the integrated process outperformed various scenarios, achieving significant water recovery almost a 2-fold increase in a single process, and notable reductions in Chromium mass (485.3 gr) and abatement (31.4 mg/h). The economic analysis indicated that the benefit-cost ratio of the integrated process is slightly higher compared to hybrid ADS-MD primarily because of the lower costs in SSF. Ultimately, the results underscored the process of SSF and ADS in boosting MD performance, particularly in water production and Chromium reduction, with prudent economic considerations.

An Effective Standalone Solar Air Gap Membrane Distillation Plant for Saline Water Desalination: Mathematical Model, Optimization

Several drinking water production techniques are being established to respond immediately to the growing needs of the population. The system of air gap membrane distillation (AGMD) is the best attractive option for the process of water desalination. This thermal process is characterized by its potential to provide drinking water at low energy costs when combined with solar energy. In this paper, the AGMD brackish water desalination unit potentialities coupled with solar energy were investigated. Ghardaïa of the south region has been considered as the field of our study. Mathematical modeling is investigated by employing MATLAB software to develop the prediction of the permeate flux related to the phenomena of heat and mass transfer. Herein, flat plate solar collectors (SFPC) were exploited as a source for heating saline water through free solar energy conversion. The further model validation of a flat solar collector made it possible for following the instantaneous evolution of the collector outlet temperature depending on the feed water temperature and the flow rate. Furthermore, it is interesting to note that the results prove the possibility to produce water by the solar AGMD process with a maximum permeate flux of 8 kg·m−2·h−1 achieved at 68 °C, a feed temperature. Moreover, gained output ratio (GOR) of the unit of thermal solar desalination was estimated to be about 4.6, which decreases with increasing hot water flow and temperature.

Detailed numerical analysis of air gap membrane distillation performance using different membrane materials and porosity

The motivation of this computational research is to comprehensively analyze the performance of the air gap membrane distillation (AGMD) process by varying the membrane porosity at different inlet feed temperatures (Tfeed) in counter-current and co-current flow regimes. This computational study also includes the comparative study of different membrane materials with different porosities. In this research work, a detailed theoretical model for porous medium with phase change is formulated and presented to evaluate the permeate mass flux, heat flux, and evaporation efficiency of the AGMD technique. Additionally, a CFD numerical model is successfully developed and validated with the previously published data.The results reveal that high evaporation efficiency is achieved at about 90 %, 92 %, and 94 % with 90 % membrane porosity at different inlet feed temperatures of 50 °C, 60 °C, and 75 °C, respectively, in both flow regimes. Also, transported mass flux was enhanced by 43 % at Tfeed, 50 °C with high porosity, while it increased by 65 % at Tfeed, 75 °C. The AGMD thermal performance using PVDF and PTFE flat sheet membranes is comparable with the same membrane thickness and at the same porosity; however, PTFE offers relatively high evaporation efficiency and mass flux, especially at low inlet feed temperature (50 °C).

Surface modification of porous polyvinylidene fluoride hollow fiber membrane by sulfonated poly(ether ether ketone) coating for membrane distillation of oily wastewater

AbstractHighly porous polyvinylidene fluoride hollow fiber membranes were fabricated by a non‐solvent induced phase separation process. The membranes were modified by coating an ultra‐thin hydrophilic layer of sulfonated poly(ether ether ketone) (sPEEK) onto the inner surface. An industrial oily wastewater treatment was performed through an air gap membrane distillation (AGMD) process. From field emission scanning electron microscopy, the modified membrane showed an open structure with a large finger‐like outer layer and sponge‐like inner layer. The thickness of the coated sPEEK layer on the inner surface was about 0.5 μm. The coated membrane presented mean pore size of 36 nm and overall porosity of 73%. The inner surface water contact angle decreased from about 82° to 57°. Using Langmuir adsorption experiment, minor oil adsorption on the modified membrane surface was confirmed. A stable water flux of about 12 kg m−2 h−1 and oil rejection of 99% were found during 72 h of the AGMD process for treating the oily wastewater of NGL‐900 (Gachsaran, Iran) plant. The high flux recovery ratio of about 98% was related to the improved anti‐oil‐fouling property. The modified membrane can be a potential candidate for oily wastewater treatment through the MD processes.

Air gap membrane distillation applied to olive mill wastewater

In Mediterranean countries, the olive industry is a major economic sector. During the production of olive oil, a wastewater is generated namely, olive mill wastewater (OMW). This OMW needs to be treated otherwise it pollutes the environment. To lower the pollutants load air gap membrane distillation (AGMD) process is investigated. This study is focusing on investigating the effect of OMW feed temperature and flow rate in addition to membrane pore size on the performance of AGMD. Three different feed temperatures (50, 60, and 70 °C) along with three different feed flow rates (2, 3, and 4 ml/s) were employed. The utilized membranes were made of polytetrafluoroethylene (PTFE) having pore sizes of 0.2 and 0.45 µm. The major conclusion of this work is that all AGMD permeate samples have zero total phenols (TPh) and zero total solids (TS), however, their chemical oxygen demand (COD) values were around 17,700 and 20,400 mg/L for 0.2 and 0.45 µm membranes respectively. These results are considered low enough for the permeate to be allowed to be sent to centralized domestic wastewater treatment plants. In addition, a mathematical model was developed to calculate COD, TPh, TS and TSS (total suspended solids). The calculated values of these parameters were in good agreement with their measured counterparts. The activation energies of utilized membranes (0.2 and 0.45 µm) were calculated from experimental results and were found to be 50.7 and 49.1 kJ/mol respectively, whereas the mass transfer coefficients were 28.1 and 32.1 kg/m2.h.bar respectively.

Activated carbon as a photothermal absorber in PVDF membranes for solar driven air-gap membrane distillation

Renewable energy-enabled desalination systems are crucial for solving the global water scarcity challenges in an environmentally friendly manner. In this work, we report an air gap membrane distillation (AGMD) process that utilizes polyvinylidene fluoride (PVDF) membranes blended with a photothermally active and relatively inexpensive activated carbon (AC). The composite membrane absorbed the solar radiation and generated local heat at the membrane surface, providing the driving force required in the AGMD process. This strategy overcame one of the key limitations of traditional MD—temperature polarization, and increased the energy efficiency significantly. We show that the blending of 5 to 9 %AC into the PVDF matrix can significantly boost the solar-energy-driven flux of AGMD by 281–1400 %, compared to the pristine membrane. PVDF membrane blended with 9 %AC exhibited an average AGMD permeate flux of 0.31 kg.m−2.h−1, with a GOR of 0.29 and a photothermal efficiency of 17.64 %. All PVDF-AC membranes showed excellent salt rejection, reaching 99.9 % for PVDF-9%AC. Finally, the AGMD performance of the fabricated membranes was compared by estimating their normalized MD coefficients (B/δ). PVDF-9%AC exhibited a B/δ value of 18.8E-5 kg s−1 m−3 Pa−1, as opposed to a meager 0.89E-5 kg s−1 m−3 Pa−1 exhibited by its pristine counterpart.

Membrane Distillation Technology Using for Desalination of Associated Oil Water Production and Study Efficiency of Feed Water Operation Parameter on Air Gap Membrane Distillation Process Production

In this study; membrane distillation technology using to associated oil water production desalination by air gap membrane distillation unit to removed salt from the water after separating oil product, via PTEF commercial hydrophobic membrane distillation with 0.22 µm porous and 0.011 m contact surface area, evaluated the desalination system and operation parameter for feed water effected on process production by employment the distillation under boiling point temperature that getting commercial increments and study the energy gain by calculating the GOR of the desalination process.
 The study focusing on the air gap membrane distillation desalination process by a range of temperature after primary simple sedimentation and filtration it's obtained salt rejection up to 98.9% that proves process separation efficiency. Evaluated the mean operation parameters of feed water affected on permeate water production when selected the feed temperature and flow rate with fixed coolant temperature, coolant flow rate, and air gap width to get an optimum range for feed water operation parameter to obtain optimum value to permeate water production and saving energy.

Performance improvement of an air gap membrane distillation process with rotating fan

The current paper presents an experimental study on the performance of a novel air gap membrane distillation (AGMD) desalination system where a fan blade is installed within the air gap to improve the system’s productivity and energy utilization. The installed blade creates suction inside the air gap behind the membrane and increases the air turbulence, thereby reducing the vapor mass transfer resistance across the membrane and improving the productivity and energy efficiency of the system. Results revealed that the proposed design and process improve the vapor permeate flux by about 250% when compared to the conventional AGMD module. Furthermore, the average improvement in the gained output ratio of the system is about 67%, with a corresponding 77% reduction in the specific thermal energy consumption. Influences of the feed temperature and the motor speed are dominating the performance of the new system.

Thermo-economic and design analysis of a solar thermal power combined with anaerobic biogas for the air gap membrane distillation process

In this paper, a novel layout of concentrating solar power linked in series with anaerobic digestion is presented to power an Organic Rankine cycle (ORC-Toluene) and Air Gap Membrane Distillation (AGMD) for desalination and electric power generation. The novelty emerges from some facts which are centralized around the use of a hybrid electric generation via Concentrated Solar Power (CSP) and anaerobic digestion biogas to achieve higher stability and profitability. Meanwhile, the cogeneration through the waste heat of the ORC drives the AGMD, which benefits as well from the higher stability due to hybridization. The proposed system has been designed through advanced modeling in the MATLAB/ Simulink® that facilitates the interaction of the individual energy technologies efficiently.To ensure reliability, the anaerobic digestion process has been used as a backup unit to compensate for the absence of solar energy and for the disposal of organic waste. A technical sensitivity analysis has been conducted for all the system units in order to reduce the respective design limits and identify optimum operational windows. The investigations are preformed based on energy, exergy, and cost analyses to produce 100–1500 m3/day of freshwater. The results reveal that the total hourly costs are found within the range of 30–70$/h which are considered to be remarkable results when comparisons are made with the conventional desalination processes. The range of total water price, $/m3 was found to fluctuate between 0.5 and 1.45$/m3. The performance of the model has been tested in a rural area in Oman, and a thorough thermo-economic analysis of the integrated system has been conducted.

Downstream variations of air-gap membrane distillation and comparative study with direct contact membrane distillation: A modelling approach

Air-Gap Membrane Distillation (AGMD) promises to reduce heat loss in membrane distillation. Most AGMD models are one-dimensional and do not consider the downstream variations. In addition, a linear function of vapour pressure is used, which either relies on experimentally determined parameters or a simplified mass transfer resistance to model the water permeate flux. This study introduces a new, improved model that simultaneously considers both heat and mass transfer in the AGMD process by coupling the continuity, momentum, and energy equations. A novel precise logarithmic function of vapour pressure was derived to model the water permeate flux, independent of experimentally determined parameters. By varying the inlet temperature, Reynolds number, inlet concentration, and air-gap thickness, the performance of AGMD was evaluated. The results revealed that our model improved the water flux prediction from more than 10% to less than 4% deviation from experimental results. Among the operating conditions, only increasing the Reynolds number improved all the system performance metrics, including higher water flux and lower temperature and concentration polarisation effects. Results were compared with Direct Contact Membrane Distillation (DCMD) outcomes and showed that unlike AGMD, DCMD suffers from a substantial decrease in water flux along the module. For DCMD, the exit water flux value decreased by 50% in comparison with the inlet value, while the water flux decreased by only 2% for AGMD, using a 1 mm air gap thickness.

Surfaces with Adjustable Features-Effective and Durable Materials for Water Desalination.

Materials based on PVDF with desirable and controllable features were successfully developed. The chemistry and roughness were adjusted to produce membranes with improved transport and separation properties. Membranes were activated using the novel piranha approach to generate OH-rich surfaces, and finally furnished with epoxy and long-alkyl moieties via stable covalent attachment. The comprehensive materials characterization provided a broad spectrum of data, including morphology, textural, thermal properties, and wettability features. The defined materials were tested in the air-gap membrane distillation process for desalination, and improvement compared with pristine PVDF was observed. An outstanding behavior was found for the PVDF sample equipped with long-alkyl chains. The generated membrane showed an enhancement in the transport of 58–62% compared to pristine. A relatively high contact angle of 148° was achieved with a 560 nm roughness, producing a highly hydrophobic material. On the other hand, it was possible to tone the hydrophobicity and significantly reduce adhesion work. All materials were highly stable during the long-lasting separation process and were characterized by excellent effectiveness in water desalination.

Experimental and simulation study of multichannel air gap membrane distillation process with two types of solar collectors

Solar thermal energy for membrane distillation desalination is a green and safe way for areas where water scarcity and solar irradiance are strongly correlated. In this paper, a commercial-scale of desalination plant was installed and tested to study the performance of a multichannel spiral-wound air gap membrane distillation module with an area of 14.4 m2. Air gap membrane distillation desalination plant at Port Said university was powered by solar energy using flat plate and evacuated tube collectors. The model validation was carried out. The solar desalination systems were numerically simulated using the program TRNSYS under different weather conditions throughout the year. The influence of the main operating parameters (feed flow rate and inlet temperatures of evaporator and condenser) was investigated. Regression analysis agreed with experimental data fitting using a quadratic polynomial model with coefficients of determination (R2) values of 0.997, 0.972, and 0.999 for permeate flux, outlet feed temperature, and outlet coolant temperature, respectively. The results showed that the permeate flux of the air gap membrane distillation with the evacuated tube collectors was 18.81%–30.44% higher than flat plate collector, and its cost was 22.48% lower. The specific thermal energy consumption of the air gap membrane distillation system ranged from 158.83 kWh/m3 to 346.55 kWh/m3. The maximum gain output ratio reaches 4.4 at 52 °C, depending on the feed inlet temperature. The thermal efficiency of the air gap membrane distillation system is 72%. The proposed air gap membrane distillation system produced 28.78 m3/year of fresh drinking water at a cost of USD 14.73/m3 with remarkable reducing in carbon dioxide emissions by 7,274.45 kg/year.

Modification of porous polyetherimide hollow fiber membrane by dip-coating of Zonyl® BA for membrane distillation of dyeing wastewater.

Wetting and fouling have significantly affected the application of membrane distillation (MD). In this work, a dip-coating method was used for improving surface hydrophobicity of the polyetherimide (PEI) hollow fiber membrane. An air gap membrane distillation (AGMD) process was applied for treatment of the methylene blue (MB) solution. The porous PEI membrane was fabricated by a dry-wet spinning process and the hydrophobic 2-(Perfluoroalkyl) ethanol (Zonyl® BA) was used as the coating material. From FESEM, the modified PEI-Zonyl membrane showed an open structure with large finger-like cavities. The modified membrane displayed a narrow pore size distribution with mean pore size of 0.028 μm. The outer surface contact angle of the PEI-Zonyl membrane increased from 81.3° to 100.4° due to the formation of an ultra-thin coated layer. The pure water flux of the PEI-Zonyl membrane was slightly reduced compared to the pristine PEI membrane. A permeate flux of 6.5 kg/m2 h and MB rejection of 98% were found for the PEI-Zonyl membrane during 76 h of the AGMD operation. Adsorption of MB on the membrane surface was confirmed based on the Langmuir isotherm evaluation, AFM and FESEM analysis. The modified PEI-Zonyl membrane can be a favorable alternative for AGMD of dyeing wastewaters.

Carbon nanohorn improved durable PVDF membranes - The future of membrane distillation and desalination

Novel durable, hybrid separation materials based on the PVDF support and single walled nanohorn (SWCNH) were generated by a facile and efficient method. Three types of SWCNH, pristine, treated with ultrasounds, and oxidized, were applied to cover the PVDF-material. The extended characterization of the produced materials provided a broad spectrum of data including morphology, textural properties, surface ζ potential and wettability features. For the first time, the defined materials were finally tested in the air gap membrane distillation process for desalination, and the improvement was observed comparing to the PVDF. It was revealed that via the simple pretreatment method of SWCNH, it was possible to control wettability and material performance. Very important finding was that the hybrid membranes exhibited the improved permeate flux for hybrids. The enhancement was in the range of 14–27% for materials with pristine and ultrasound treated SWCNH. However, for hybrids with oxidized SWCNH 23%-improvement in transport was observed. Owing to the significantly differentiated character of pristine and oxidized SWCNH and the presence of hydrophobic support inside the structure of hybrids, separation materials with the external layer ranging from hydrophilic (contact angle 6°) to superhydrophobic (contact angle 165°) features were created.

Influence of Module Length on Water Desalination Using Air Gap Membrane Distillation Process: An Experimental Comparative Study

The impact of the membrane module length on the air gap membrane distillation (AGMD) process performance was investigated experimentally under various operating parameters. In this work, two different lengths of the AGMD module (i.e., 0.59 m and 0.28 m) were tested separately to get the optimum in terms of lower energy consumption and higher water output. The mechanism of mass and heat transfer in the AGMD process is considered as well. The experimental results were subjected to the two-way analysis of variance (ANOVA) to examine the significant influence of operating parameters and modules at p 0.05) on the gained output ratio (GOR), energy consumption (STEC), and heat input (QH.I). Under optimal operating parameters of a flow rate of 18 L/h, feed temperature of 60 °C, coolant temperature of 20 °C, and feed salinity of 5000 mg/L, the Pw and GOR were increased by 64.50% and 50.00%; the STEC and QH.I were reduced by 57.78% and 34.09%, respectively, from the long module to the short one. Thence, changing the length of the membrane module from 0.59 to 0.28 m promoted remarkably the performance of the AGMD process.

Separation of HCl/water mixture using air gap membrane distillation, Taguchi optimization and artificial neural network

Abstract The aim of this paper is to analyze the performance of the air gap membrane distillation (AGMD) process for the separation of HCl/Water mixture first by applying Taguchi optimization approach and second by developing an artificial neural network (ANN) model. The experimental data which are fed as input to the above approaches are collected from the fabricated AGMD lab-scale setup using poly-tetra-fluoro-ethylene membrane of 0.22 µm pore size. The process input variables considered are bulk feed temperature, feed flow rate, air gap thickness, cooling water temperature and cooing water flow rate and AGMD performance index is the total permeate flux. The optimum operating condition is found to be at feed temperature 50 °C, air gap thickness 7 mm, cooling water temperature 5 °C and feed flow rate 10 lpm. Analysis of variance test is carried out for both Taguchi and ANN models. Regression model has also been developed for the comparison between experimental and model predicted data. The developed ANN model has been found well fitted with experimental data having R 2 value of 0.998. Based on the calculated percentage of contribution of each input parameter on the AGMD permeate flux, it can be concluded that feed temperature and air gap thickness have highest weightage whereas feed flow rate and cooling water temperature have moderate effects. Predictive ability of the developed ANN model is further checked with 2D contour plot. The distinctive feature of the paper is the development of the Taguchi experimental design and ANN model and then consequently integration of both Taguchi and ANN has been carried out to optimized the developed ANN model parameters.

Modeling of Air-Gap Membrane Distillation and Comparative Study with Direct Contact Membrane Distillation

Most of the developed models for the air-gap membrane distillation (AGMD) process are one-dimensional and rely on experimentally determined parameters. Herein, inspired by the effectiveness-number ...

Step-by-step improvement of mixed-matrix nanofiber membrane with functionalized graphene oxide for desalination via air-gap membrane distillation

A straightforward three-stage method was applied to fabricate a super-hydrophobic mixed-matrix nanofiber membrane using the electrospinning method for desalination purpose. First, a hydrothermal technique was applied to synthesize a super-hydrophobic nano-sheet, called octadecylamine-reduced graphene oxide (ODA-rGO) with a water contact angle of 162°, which was then added to PVDF-HFP dope solution. After, 0.005 wt% LiCl was added to the dope solution to decrease the mean pore size by increasing solution conductivity. Moreover, some membranes were hot-pressed to improve liquid entry pressure (LEP). Eventually, a top-quality nanofiber membrane was synthesized using 0.1 wt% ODA-rGO and 0.005 wt% LiCl, and hot-pressed, named by MLH-0.1. By applying these stepwise improvements, the mean pore size reduced from 1.30 to 0.24 µm and LEP significantly increased from 30.4 to 127.6 kPa, compared to a neat electrospun nanofiber membrane. Finally, MLH-0.1 was tested in the air gap membrane distillation process for desalination of an aqueous solution containing 3.5 wt% NaCl. MLH-0.1 demonstrated the maximum flux of 21.1 kg/m2.h at temperatures of 70℃ and 20℃ for the feed and the permeation sides, respectively, as well as a remarkable and stable salt rejection of 99.99% for 4 days.

FABRICATION OF COMPOSITE MEMBRANES FOR WATER DESALINATION BY ELECTRON-BEAM DEPOSITION OF A POLYTETRAFLUOROETHYLENE-LIKE COATING ON THE SURFACE OF TRACK-ETCHED MEMBRANE

The present paper describes the method for the formation of polymer coatings on the poly(ethylene terephthalate) track-etched membrane surface by electron-beam deposition of polytetrafluoroethylene-like in a vacuum. It is found that the usage of this method leads to substantial hydrophobization of the membrane surface layer. The water contact angle of the deposited coatings changes from 130° to 155°, depending on the coating thickness. This change is due to the development of roughness of the deposited layer having hydrophobic properties. It is shown that the membranes of the developed sample provide a high selectivity of separation and water production rate during desalination of an aqueous salt solution of by air gap membrane distillation process and can be used for desalination of seawater.