Enhanced performance of PVDF nanocomposite membrane by nanofiber coating: A membrane for sustainable desalination through MD

Evaluation of hollow fiber-based direct contact and vacuum membrane distillation systems using aspen process simulation

Membrane distillation (MD) is a thermally driven separation process. There are four types of MD: direct contact membrane distillation (DCMD), vacuum membrane distillation (VMD), air gap membrane distillation (AGMD) and sweep gas membrane distillation (SGMD). MD process has a number of potential advantages, namely, low operating temperature and hydraulic pressure, very high rejection of nonvolatile solutes, smaller footprint and potentially high water vapor flux for example in DCMD compared to conventional thermal distillation processes. For such reasons, MD has been considered as an emerging new technology in desalination and wastewater treatment. This chapter addresses a variety of applications of MD employing primarily the techniques of DCMD, VMD, and AGMD. State-of-the-art research results in different areas such as, desalination of seawater and brackish water, produced water treatment from oil exploration and coal seam gas production, high temperature DCMD, water treatment in bioreactors and oily wastewaters, treatment of processing streams from dairy, food, beverage industries and animal husbandry, concentration of acids, membrane distillation in biorefineries, mineral recovery and radioactive water treatment, are briefly presented and discussed in this chapter.

An integrated membrane distillation (MD) flowsheet, consisting of direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) units, was proposed and analysed in terms of thermal performance and water recovery factor, for the first time. The same lab-scale membrane module (40 cm2) was used for carrying out experiments of DCMD and VMD at fixed feed operating conditions (deionised water at 230 L/h and ~40 °C) while working at the permeate side with deionised water at 18 °C and with a vacuum of 20 mbar for the DCMD and the VMD configuration, respectively. Based on experimental data obtained on the single modules, calculations of the permeate production, the specific thermal energy consumption (STEC) and the gained output ratio (GOR) were carried out for both single and integrated units. Moreover, the calculations were also made for a flow sheet consisting of two DCMD units in series, representing the “traditional” way in which more units of the same MD configuration are combined to enhance the water recovery factor. A significant improvement of the thermal performance (lower STEC and higher GOR) was obtained with the integrated DCMD–VMD flowsheet with respect to the DCMD units operating in series. The integration of DCMD with VMD also led to a higher permeate production and productivity/size (PS) ratio, a metric defined to compare plants in terms of the process intensification strategy.

A comparison of vacuum and direct contact membrane distillation for phosphorus and ammonia recovery from wastewater

Experimental mass transfer comparison between vacuum and direct contact membrane distillation for the concentration of carbonate solutions

This work investigated the influence of dye class on permeate flux and color rejection by comparing direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) applied to remediation of dyeing wastewater. The same operating system at the feed side was used and the driving force of each configuration was determined. Reactive and disperse dye solutions were considered, and a commercial membrane was employed. Final color rejection > 90.79% was obtained, and water was recovered at the permeate side (final normalized permeate flux up to 38.92 kg m−2day−1kPa−1). VMD showed higher normalized permeate flux when compared to DCMD. However, the performance according to dye class depended on MD configuration. Reactive dye resulted in higher permeate flux than the disperse dye solution in DCMD. Contrarily, disperse dye solution showed higher permeate flux in VMD. The formation of a concentration boundary layer at the permeate membrane interface was suggested with disperse dye solution in DCMD, decreasing thus the driving force. In VMD, the boundary effect is negligible with disperse dye solution. This result implies that the VMD performance in the textile industry may depend more on driving force rather than the dye class of the dyeing bath.

This research is a comparative study between vacuum membrane distillation and direct contact membrane distillation technologies. The first part focuses on an energy and exergy analysis of vacuum membrane distillation and direct contact membrane distillation configurations. The results of the energy analysis show the vacuum membrane distillation has lower energy losses across the membrane compared to direct contact membrane distillation. The results of the exergy analysis show that direct contact membrane distillation requires less work compared to vacuum membrane distillation. The second part of this research focuses on modeling of temperature distribution in feed channel for DCMD and VMD. The results of the numerical solution show that the temperature polarization effort in VMD is smaller than in DCMD. The membrane temperature in VMD approach constant temperature case and this reduces dissipated energy in the membrane distillation process.

Membrane distillation (MD) is an evaporation/condensation process of volatile components through a hydrophobic porous membrane. The maintenance of gas phase inside the membrane pores is a fundamental condition required to carry out the MD process. A hydrophobic nature of the membrane prevents liquid penetration into the pores. Membranes having these properties are prepared from polymers with a low value of the surface energy, such as polypropylene (PP), polytetrafluoroethylene (PTFE) or polyvinilidene fluoride (PVDF) (Alklaibi & Lior, 2005; Bonyadi & Chung, 2009, Gryta & Barancewicz, 2010). Similar to other distillation processes also MD requires energy for water evaporation. The hydrodynamic conditions occurring in the membrane modules influence on the heat and mass transfers, and have a significant effect on the MD process efficiency. The MD separation mechanism is based on vapour/liquid equilibrium of a liquid mixture. For solutions containing non-volatile solutes only the water vapour is transferred through the membrane; hence, the obtained distillate comprises demineralized water (Alklaibi & Lior, 2004; Gryta, 2005a; Schneider et al., 1988). However, when the feed contains various volatile components, they are also transferred through the membranes to the distillate (ElBourawi et al., 2006; Gryta, 2010a; Gryta et al., 2006a). Based on this separation mechanism, the major application areas of MD include water treatment technology, seawater desalination, production of high purity water and the concentration of aqueous solutions (El-Bourawi et al., 2006; Drioli et al., 2004, Gryta, 2006a, 2010b; Karakulski et al., 2006; Martinez-Diez & Vazquez-Gonzalez, 1999; Srisurichan et al., 2005; Teoh et al., 2008). A few modes of MD process are known: direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), sweeping gas membrane distillation (SGMD), vacuum membrane distillation (VMD) and osmotic membrane distillation (OMD). These variants differ in the manner of permeate collection, the mass transfer mechanism through the membrane, and the reason for driving force formation (Alklaibi & Lior, 2005; Gryta, 2005a). The most frequently studied and described mode of MD process is a DCMD variant. In this case the surfaces of the membrane are in a direct contact with the two liquid phases, hot feed and cold distillate (Fig. 1). The DCMD process proceeds at atmospheric pressure and at temperatures that are much lower than the normal boiling point of the feed solutions. This allows the utilization of solar heat or so-called waste heat, e.g. the condensate from turbines or heat exchangers (Banat & Jwaied, 2008; Bui et al., 2010; Li & Sirkar, 2004).

A desalination is a promising approach to addressing the freshwater scarcity caused by limited freshwater resources and salt intrusion (pollution). Membrane distillation (MD) was proposed as a possible technology for desalination. This study review the efficiency of membrane distillation by comparing the permeate flux and thermal energy efficiency of the four configurations, namely, direct contact membrane distillation (DCMD), vacuum membrane distillation (VMD), air gap membrane distillation (AGMD) and sweeping gas membrane distillation (SGMD). It was observed that the sequence of permeate flux and thermal energy efficiency is VMD> DCMD> SGMD>AGMD and VMD> SGMD> AGMD> DCMD, respectively. The results show that the VMD provides the highest permeate flux at 15.2 kg/hm2 with 99.25% of salt rejection rate. Additionally, VMD possess good energy efficiency at 66% relative to other configuration at the recorded permeate flux. Subsequently, the feasibility of MD in desalination is studied using different case studies. Furthermore, the effect of operating parameters (feed temperature, feed concentration, feed flow rate, and long-term operation) on flux is discussed. The results suggested that the flux increases when feed temperature or feed flow is increased. At the same time, the flux will decrease when feed is in high concentration and long-term operation.

Effects of superhydrophobic SiO2 nanoparticles on the performance of PVDF flat sheet membranes for vacuum membrane distillation

Experimental comparison of direct contact membrane distillation (DCMD) with vacuum membrane distillation (VMD)

Novel porous composite hydrophobic/hydrophilic polysulfone membranes for desalination by direct contact membrane distillation

This paper presents a comparative performance study of single-stage desalination processes with major configurations of membrane distillation (MD) modules. MD modules covered in this study are (a) direct contact MD (DCMD), (b) vacuum MD (VMD), (c) sweeping gas MD (SGMD), and (d) air gap MD (AGMD). MD-based desalination processes are simulated with rigorous theoretical MD models supported by molecular thermodynamic property models for the accurate calculation of performance metrics. The performance metrics considered in MD systems are permeate flux and energy efficiency, i.e., gained output ratio (GOR). A general criterion is established to determine the critical length of these four MDs (at fixed width) for the feasible operation of desalination in a wide range of feed salinities. The length of DCMD and VMD is restricted by the feed salinity and permeate flux, respectively, while relatively large AGMD and SGMD are allowed. The sensitivity of GOR flux with respect to permeate conditions is investigated for different MD configurations. AGMD outperforms other configurations in terms of energy efficiency, while VMD reveals the highest permeate production. With larger MD modules, utilization of thermal energy supplied by the hot feed for evaporation is in the order of VMD > AGMD > SGMD > DCMD. Simulation results highlight that energy efficiency of the overall desalination process relies on the efficient recovery of spent for evaporation, suggesting potential improvement in energy efficiency for VMD-based desalination.

Evaluation of energy requirements in membrane distillation

To develop an inexpensive and simple technology and increase anti-oil fouling resistance for membrane distillation applications, a hydrophilic/oleophobic nanocomposite membrane was fabricated by using SiO2/Chitosan (CT) sol solution coating with different volume ratios (0.5 : 1, 1 : 1 and 2 : 1 v/v) on PVDF membrane surface. The formation of SiO2/CT layer on membrane surface was confirmed by Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDX). The influence of hydrophilic nanocomposite layer on the characteristics of membranes, including in-air water contact angle, morphology, porosity, liquid entry pressure of water (LEPw) and direct contact membrane distillation (DCMD) performance, was investigated. The results show that the composite membrane (SiO2/CT (1 : 1 v/v)- PVDF membrane) by adding of 0.5 and 1 g/L gasoline concentrations not only incurred fouling but also a higher flux with respect to the neat membrane in each gasoline concentration. During 8 hours continuous desalination process of saline gasoline emulsion solution (20 gr/L NaCl solution containing 0.5 gr/L gasoline), it was found that all modified membranes had high performance stability in comparison with the neat membrane, the modified membrane showed high performance stability and flux without decreased salt rejection (99.9%). At the end, we conducted performance comparison between the prepared membranes in current work and presser based process.