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Comparative studies of different membrane distillation configurations and membranes for potential use on board cruise vessels
... Thermal desalination processes such as MED and MSF were used for freshwater production on ships. Currently, there is a shift in this trend towards the MD process, as evident from scientific reports in which the input heat to MD is derived from the ship's cooling water [105][106][107][108]. Xu et al. [105] reported a pilot VMD system using waste heat from ships for examining operational conditions of polypropylene (PPE) hollow fibers. ...
... The feed water was heated by heat generated by vessel motor, and 99.99% salt rejection with 5.4 LMH flux was obtained. Comparative studies of various MD structures and membranes to allow possible use of waste heat produced in the engine cooling system have carried out onboard cruise vessels [106]. In any test, the permeate content was good, and virtually all ions were extracted. ...
... © 2018, Elsevier). Reproduced with permission from[106]. ...
Water and energy are critical components for human, and govern the growth and progress of societies. Desalination is an important process to meet ever-increasing water demand, although it is an energy-intensive alternative compared to conventional water treatment techniques. Demand for desalination has been expanded rapidly as traditional water sources are getting overexploited. Membrane distillation (MD) is a promising water treatment process for highly saline water, including reject from the reverse osmosis plants. To compensate for high energy requirement for the MD process, low-grade heat sources (such as waste heat or renewable sources) can be used. Limitations of other desalination processes are discussed in this review to underline evolution and tweaking of alternatives for making them optimal. In this review, we examine the suitability of the MD process for harnessing energy from different types of low-grade heat sources to make it cost-effective. Financial aspects of the MD process for different heat sources are also highlighted. A summary of studies focusing on hybrid MD systems is also provided. Finally, challenges, opportunities and current implementation of the MD process by using low-grade heat-based MD systems are discussed.
... Small-scale seawater MD desalination systems have also been trialled for fresh water supply on ships to exploit the waste heat generated from the ship engines [50,51]. So far, fresh water provision on most cruise ships relies on the mature seawater desalination processes including RO and MSF [51]. ...
... Small-scale seawater MD desalination systems have also been trialled for fresh water supply on ships to exploit the waste heat generated from the ship engines [50,51]. So far, fresh water provision on most cruise ships relies on the mature seawater desalination processes including RO and MSF [51]. As a pressure-driven desalination process, RO requires electricity generated from the ship engines to operate high-pressure pumps, thus increasing the carbon footprint and operational cost of cruise ships. ...
... The product water from the MD process had salt concentration < 3 mg/L and met the drinking water standard. In another study, Amaya-Vías et al. [51] investigated and compared the performance of different MD configurations (e.g. direct contact, water gap, and air gap) on cruise ships, exploiting the residual heat of the ship engine jacket water. ...
Purpose of Review
Membrane distillation (MD) has been known as a promising water treatment process for many years. However, despite its advantages, MD has never been able to compete with other processes for industrial water treatment and supply. Instead, it has been orientated towards several unique strategic water treatment applications. This review aims to uncover the opportunities and technical challenges pertinent to the MD process and the current status of its strategic water treatment applications most notably including decentralised small-scale desalination for fresh water provision in remote areas, hybridisation with forward osmosis (FO) for treatment of challenging polluted waters, regeneration of liquid desiccant solutions for air conditioning, and treatment of acid effluents for beneficial reuse.
Recent Findings
Pilot and small-scale MD systems have been demonstrated for decentralised desalination using various renewable energy sources to supply fresh water in remote, rural areas and on ships where other desalination processes are inefficient or unfeasible. For this strategic desalination application, MD is technically viable, but more works on configuration modification and process optimisation are required to reduce the process energy consumption and water production costs. For the three other strategic applications, the technical viability of the MD process has been proved by extensive lab-scale researches, but its economic feasibility is still questionable due to the lack of large-scale evaluation and the uncertain costs of MD systems.
Summary
The orientation of MD towards strategic water treatment applications is clear. However, huge efforts are required to facilitate these applications at commercial and full scale.
... In this paper, the purpose was to perform a MD cost estimate analysis that allows broad comparisons between different MD configurations and desalination technologies. In order to make the analysis as realistic as possible, boundary conditions were validated through various experiments using a laboratory MD setup ( Figure 2) reported elsewhere [65]. Based on these boundary conditions and the suggested assumptions, simulations were performed using validated cost calculation methods, which are described in the following sections and supported extensively by literature. ...
... This boundary condition must be taken into account for cost estimates as it may affect some elements of an MD process, such as storage tanks. Table 2. MD laboratory system design and main operating conditions for seawater desalination [65]. ...
... Furthermore, thermal pollution of a natural water body is thereby avoided. An example of industrial applications of this MD scenario include water treatment of the petrochemical and gas industry, power plants or desalination related to maritime navigation, as in the case of desalination on board cruise ships, see, for example, [65]. Equally important is the solar heat scenario. ...
Membrane distillation (MD) has a great deal of potential and this is currently being explored by the scientific community. However, this technology has not yet been implemented by industry, and an estimation of final product costs is key to its commercial success. In this study a techno-economic assessment of air gap MD (AGMD) and water gap MD (WGMD) for seawater desalination under different capacities and heat source scenarios was developed. The simplified cost of water (SCOW) method, which estimates investment costs, fixed and variable costs, as well as amortization factors and price influence over time was applied. In addition, experimental data from a laboratory-scale MD desalination plant were also used. The results showed water costs in the range of 1.56 to 7.53 €/m3 for WGMD and 2.38 to 9.60 €/m3 for AGMD. Specifically, the most feasible scenario was obtained for WGMD with a capacity of 1000 m3 daily using waste and solar heat. Finally, the costs obtained for MD were similar to those of conventional desalination technologies at the same scale factor. Therefore, although large-scale pilot studies and optimization of manufacturing processes are needed, MD shows very promising results that should be considered further.
... The configurations that have been developed in MD process are DCMD, VMD, AGMD, SGMD, LGMD, TSGMD, and VA-AGMD Rivier et al., 2002;Ugrozov et al., 2003;Ugrozov and Kataeva, 2004;Khayet and Matsuura, 2011e;Adham et al., 2013;Essalhi and Khayet, 2014;Prince et al., 2015;Ashoor et al., 2016;Deshpande et al., 2017;Liu Z. et al., 2017;Amaya-Vías et al., 2018). The schematic diagrams representing the heat and mass transfer for these configurations using plate and frame module and flat sheet membranes are presented in Figures 1-7. ...
... Liquid or water gap membrane distillation (LGMD/WGMD), which emerged from the combinations of DCMD and AGMD configurations, was proposed by Ugrozov et al. (2003). Unlike AGMD where empty air gap exists between membrane and cooling plate, in LGMD as shown in Figure 5, the gap between membrane and condensing surface in permeate side of the module is filled with distilled water, which acts as stagnant cold liquid solution inside membrane module (Ugrozov and Kataeva, 2004;Amaya-Vías et al., 2018). Water vaporizes on feed side of membrane module, diffuses through membrane pores and condenses in the liquid gap between membrane and cooling plate on permeate side of membrane (Essalhi and Khayet, 2014;Amaya-Vías et al., 2018). ...
... Unlike AGMD where empty air gap exists between membrane and cooling plate, in LGMD as shown in Figure 5, the gap between membrane and condensing surface in permeate side of the module is filled with distilled water, which acts as stagnant cold liquid solution inside membrane module (Ugrozov and Kataeva, 2004;Amaya-Vías et al., 2018). Water vaporizes on feed side of membrane module, diffuses through membrane pores and condenses in the liquid gap between membrane and cooling plate on permeate side of membrane (Essalhi and Khayet, 2014;Amaya-Vías et al., 2018). A comparative study carried out between LGMD and AGMD by Essalhi and Khayet (2014), indicated that specific internal heat loss is lower for LGMD, whereas thermal efficiency is higher for AGMD. ...
Identification and mitigation of challenges associated with membrane distillation (MD) modeling are very crucial to the applicability of MD technology in the industry. Several research studies have been carried out on direct contact membrane distillation (DCMD) modeling because of its simplicity, while other MD configurations have gained little attention. Most studies conducted on MD modeling were achieved based on uniform membrane pore size and pore size distribution assumption. This study exploits the homogeneity of these assumptions to conduct a modeling review for temperature polarization (TP) and concentration polarization (CP), as they apply to MD configurations. TP and CP phenomena have been identified as two of the main challenges to advance MD modeling for further development of MD technology. Their impact are detailed in the heat and mass transfer mechanisms discussed. Thermal conductivity of common hydrophobic commercial membrane materials at different temperatures are presented in this study. The use of optimal operating flow rates, suitable membranes, and proper module design are recommended as viable solutions to reduce the effect of TP and CP on permeate flux decay.
... The authors highlighted the potential of operating process water as cooling water within the MD system, resulting in a substantial reduction in operational costs from US$ 2.62/m 3 -0.23/m 3 . Additionally, the integration of MD with WH from ship engines for onsite water desalination has been extensively documented (Fig. 9c) [147][148][149][150]. ...
... Integration of MD with waste heat: (a) Schematic diagram illustrating an MD system paired with a WH source; (Adapted from[138]) (b) Process flow chart of a power station's WH-driven DCMD pilot plant; (Adapted from[138]) (c) Schematic representation of an MD system harnessing WH from a cruise vessel engine for water desalination; (Adapted from[150]). ...
Feedwater heating represents a pivotal and energy-intensive step in membrane distillation (MD), contributing significantly to the total energy costs. Thus, elevating the thermal efficiency of the MD process is vital for its broader energy optimization. Recent years have witnessed an uptick in research targeting the enhancement of thermal efficiency in MD systems, particularly in the realm of innovative feedwater heating techniques. This comprehensive review delivers an in-depth examination of diverse feedwater heating methods utilized in MD, spanning both bulk and localized heating approaches. Bulk heating methods involve the utilization of solar panels, solar collectors, solar ponds, waste heat, and geothermal energy to heat bulk feedwater. Conversely, localized heating techniques include photothermal heating via direct solar light, joule heating, microwave-assisted heating, and induction heating. This review delves into the techno-economic viability of transitioning from bulk to localized heating in MD and provides a qualitative assessment of the inherent challenges each technology presents. Ultimately, this review is an invaluable reference for the research community, shedding light on recent advancements, developmental phases, operational methodologies, obstacles, and opportunities specific to each water heating technique within MD's framework.
... Table 1 shows schematic diagram of each MD configuration and their advantages and disadvantages. • High flux • Simple design [48] • Cannot use cold feed as coolant • High heat loss through conduction [48] • Cannot obtain pure distillate [49] AGMD [7] • Low operating temperature • Low hydrostatic pressure • Low heat loss [49] • Internal heat recovery [48] • High mass transfer resistance • Low permeate flux [50] SGMD [7] • The flux generated is not influence by inlet gas temperature [41] • Less heat loss [48] • Require a large condenser [7]. • Additional cost for sweep gas [48]. ...
... Table 1 shows schematic diagram of each MD configuration and their advantages and disadvantages. • High flux • Simple design [48] • Cannot use cold feed as coolant • High heat loss through conduction [48] • Cannot obtain pure distillate [49] AGMD [7] • Low operating temperature • Low hydrostatic pressure • Low heat loss [49] • Internal heat recovery [48] • High mass transfer resistance • Low permeate flux [50] SGMD [7] • The flux generated is not influence by inlet gas temperature [41] • Less heat loss [48] • Require a large condenser [7]. • Additional cost for sweep gas [48]. ...
Membrane Distillation (MD) is a promising technology for separation and purification processes. It is a thermally-driven separation process which allow only vapour molecules are to pass through a porous hydrophobic membrane. MD separation is driven by the vapour pressure difference existing between the porous hydrophobic membrane surfaces unlike normal membrane processes which operate on temperature difference. This paper focus on the expectation of MD treatment process primarily for the readers who have no idea about this membrane process A brief overview is given of MD before treatment process which includes membrane materials, membrane preparation techniques, membrane characteristics, module and configuration. Membrane performance during treatment process will be highlighted. Membrane fouling which is one of the major drawback of MD will be also discussed.
... There are four classifications of MD systems: direct contact membrane distillation (DCMD), air gap MD, vacuum membrane distillation (VMD), and sweeping-gas MD [8][9][10]. Owing to the simplicity and low cost of the DCMD technique, it has been investigated extensively [11,12]. ...
... k g = 0.0144 − 2.16 × 10 −5 T m + 1.32 × 10 −7 T m 2 k s = 0.178, (8) where C p is the heat capacity (J/[kg·K]), q is the heat flux (W/m 2 ), Q is the heat source (W/m 3 ), and k m is the thermal conductivity of the membrane (W/[m·K]), respectively. ε is the membrane's porosity. ...
Understanding the energy efficiency of direct contact membrane distillation (DCMD) is important for the widespread application and practical implementation of the process. This study analyzed the available energy, known as exergy, in a DCMD system using computational fluid dynamics (CFD). A CFD model was developed to investigate the hydrodynamic and thermal conditions in a DCMD module. After the CFD model was verified, it was used to calculate the temperature polarization coefficient (TPC) and exergy destruction magnitudes under various operating conditions. The results revealed that slight decreases and increases in the TPC occurred with distance from the inlet in the module. The TPC was found to increase as the feed temperature was reduced and the feed and permeate flow rates were increased. The exergy destruction phenomenon was more significant under higher feed temperatures and higher flux conditions. Although the most significant exergy destruction in the permeate occurred near the feed inlet, the effect became less influential closer to the feed outlet. An analysis of exergy flows revealed that the efficiency loss in the permeate side corresponded to 32.9-45.3% of total exergy destruction.
... These MD advantages make it a promising alternative to conventional desalination and water reuse technologies for many environmental and industrial applications (Amaya-Vías et al., 2018;Cui et al., 2018;Silva et al., 2018). Nevertheless, MD is not fully commercialized and implemented by industry (Khayet, 2011;Qtaishat et al., 2009), since many aspects have still not been studied in detail; for example, the effect of organic matter (OM) and HA in the MD process. ...
... MD testing was conducted in a laboratory system in AGMD and WGMD modes using a similar setup reported elsewhere (Amaya-Vías et al., 2018;Francis et al., 2013;Khalifa, 2015). Briefly, MD system consisted of a co-current flat sheet acrylic membrane module with an effective membrane area of 0.018 m 2 , a feed tank, a cooling tank and two peristaltic pumps (Masterflex ® L/S 77800-62, Cole-Parmer). ...
Desalination and water reuse are important means to resolve local water scarcity and security issues worldwide where membrane distillation (MD) may be part of a solution. Natural organic matter and in particular, humic acids (HA), are widely present in water supplies to be treated but exhibit little understood behavior to diffuse through MD membranes into permeate. In this work, air gap (AGMD) and water gap (WGMD) were utilized to study HA behavior in MD using seawater and synthetic water over a range of typical MD temperatures, flow rates and membrane types. HA diffusion was first shown with seawater feed then on synthetic solutions at all process conditions. While electrical conductivity rejection was always above than 99%, HA rejection showed values of 33% and 90% for AGMD and 68% and 93% for WGMD with seawater and synthetic water, respectively. Analytical techniques were used to perform a preliminary organic matter characterization in permeate, obtaining clear differences between the feed and permeate HA property. Compared to hydrophobic membranes, uniquely oleophobic membranes inhibit HA diffusion suggesting hydrophobic surface diffusion of HA through the membrane. HA flux as well as potential undesirable effects of the organic matter in permeate should be considered for MD applications.
... This DCMD and AGMD hybrid configuration known as permeate gas membrane distillation (PGMD) because in PGMD air gap between the membrane and cold condensing side filled with the permeate liquid or gas [34]. The permeate in the air gap connects directly to the membrane and serve as a stagnant cold liquid solution that allow vapours to condensate in filled permeate [35]. The stagnant cold permeates keep the specific internal heat loss lower when compared to AGMD [36]. ...
Highlights
•The MD process and electrospinning technique have been thoroughly described.
•A discussion on how to improve the anti-fouling/wetting properties of the electrospun MD membrane
•The anti-fouling/wetting advancements of the electrospun MD membrane are summarized year by year.
•Major challenges, limitations, and future suggestions to enhance electrospun MD performance
... Sustainable technologies and best practices: Underrated potential and adoption timing Improvements in propulsion technology and energy efficiency have consistently played a major role in shipbuilding, particularly over the past years, due to stricter regulations and rising energy costs (Amaya-Vías et al., 2018;Eikeland et al., 2020). Technological innovations in shipbuilding, concerning waste-treatment and management also imply cost reductions (Paiano et al., 2020), whilst improving environmental sustainability . ...
Cruise tourism research has developed exponentially during the last decades. Global tourism activity in general and cruises in particular, are concentrated in coastal areas and represent a dominant part of the so-called ‘blue economy’. Within this context, the public debate surrounding the impact of cruise tourism on port communities reflects a narrative of unsustainable growth, environmental pollution and negative globalization-related symbolism. Yet, the relatively small sizeof the cruise sector and the over-focus on emissions arguably misrepresents the overall impact and potential of this tourism domain for portside communities, economies and ecosystems. Cruise-related scientific research, as probably expected,offers a much more refined and holistic picture; transcending the somewhat populist public debate on this matter. Based on a systematic literature review examining cruise-related papers published between 1983 and 2009, Papathanassis and Beckmann (2011) identified 145 papers, which were subsequently subjected to a meta data- and a thematic-analysis. Approximately a quarter of them addressed the environmental-, social- and economic impacts of cruising on coastal regions. A decade later, and following an analogous methodological approach, a total of 305 cruise research papers,published between 2012 and 2022, yielded 161 relevant papers, subjected to the same coding scheme and thematically compared to previous findings. The subsequent thematic analysis, revealed a comprehensive set of issues, opportunities and challenges cruise tourism poses to coastal areas. Following a critical discussion of past developments and their trajectory, a future research and action agenda is proposed.
... MD is far superior as opposed to competing technologies due to the following reasons: (1) MD can achieve theoretically 100 % rejection of all non-volatile components, including inorganic ions, macromolecules etc. (2) can handle feeds at higher temperatures (while operating at lower temperatures as compared to thermal desalination processes like evaporation) (3) lower operating pressures as compared to Reverse Osmosis (RO) (Where applied pressure must be several times greater than osmotic pressure) (4) can handle high salinity feeds, (5) mechanical stability requirement is lower as compared to RO/Nanofiltration (NF) membranes, (6) able to utilize waste-heat and lowgrade energy sources and (7) can be integrated with low-grade energy sources or renewable energy [3]. MD has been widely explored for desalination and brine treatment and is now being investigated for extraction of medicinal extracts and pharmaceutical products, treatment of textile dye effluents, the concentration of fruit juices and dairy streams, etc., [4]. ...
Seawater desalination and water recovery from wastewater are potential solutions to meet the ever-growing water demand. Membrane distillation (MD) is a next-generation membrane technology that can be harnessed for sustainable water production. The advantages of the MD process and the various operating configurations are discussed. The challenges in membrane development are highlighted, and the various state-of-the-art approaches for improving membrane performance, fouling resistance, anti-wetting character, and minimizing concentration/temperature polarisations are included. The process design is another crucial aspect of the successful implementation of the MD. Response surface methodology and Analysis of Variance (ANOVA) have been explored to identify the optimal operating conditions. Machine learning and computational fluid dynamics analysis (CFD) that have been used to predict the performance and influence of the process parameters are discussed. The energetics and economics of the MD process have also been discussed. The MD process could become sustainable if it utilizes renewable energy sources (solar, geothermal) for bulk heating of the feed. This article highlights the various challenges associated with MD technology and provides an overview of the strategies researched to overcome them.
... Although the water flux of the former was high in a laboratory-based test, AGMD was confirmed to have higher water flux and higher energy efficiency in a pilot test. Amaya-Vías et al. [26] investigated the applicability of an MD configuration using waste heat from cruise ships. The removal rate and water flux according to the membrane type and MD configuration were compared, and these configurations were found to be possible alternative processes for water production in the cruise ship industry. ...
Although membrane distillation (MD) is a promising desalination process, its use is limited because it requires a large amount of thermal energy. To reduce the thermal energy consumption during MD, studies combining various renewable energy sources (e.g., solar, geothermal, and waste heat) are currently being conducted. Therefore, pilot plant experiments combining solar energy with an MD system were conducted. In particular, a module that could be changed into different MD configurations, including direct contact MD (DCMD) and air gap MD (AGMD), was reviewed. The performance of the pilot plant was analyzed for each configuration under various operating conditions and according to onsite weather conditions. Because DCMD can obtain a 43% higher water flux than can AGMD, a long-term DCMD test was conducted to achieve a high water flux. The specific energy consumption (SEC) and gained output ratio (GOR) were compared in the presence and absence of solar energy. A 30% decrease in the SEC and 17% increase in the GOR were observed for the sunny days compared with when no solar energy was used. These results indicate that combining the MD with solar energy can improve its performance during long-term operation. In addition, the cost per unit volume of product water was estimated based on the designed solar MD pilot plant.
... MSF dan MED dapat digunakan di atas kapal pesiar hingga 900 m 3 /hari/unit, dimana penggunaan teknologi MSF mendominasi [28]. Dikarenakan besarnya volume yang dibutuhkan dan ruang yang tersedia di kapal sangat terbatas, Tabel maka diperlukan teknologi yang lebih ringkas [30]. ED merupakan teknologi berbasis membran yang beroperasi karena adanya gradien listrik beda potensial listrik [24]. ...
... [88] The liquid/gas in the air gap act as a stagnant cold liquid solution inside the membrane and allow vapors to condensate in filled permeate. [89] The specific internal heat loss is lower for PGMD when compared with AGMD. [90] Therefore, a new MD hybrid configuration was constructed where the gap region of PGMD is filled with additional conductive materials such as metal mesh, metallic wool, or any porous metal medium. ...
Water is essential for the presence of life on this earth. However, water contamination due to the presence of heavy/toxic metals is one of the serious environmental issues for living beings. Several methods have been devoted to separating or removing those heavy metals from wastewater. Among them, membrane distillation (MD) has become one of the most attractive approaches due to its higher rejection rate than processes driven by pressure, lower energy consumption than traditional distillation processes. MD has gained significant attention for removing heavy metals than other techniques like ion exchange and adsorption in the last two decades. This review provides insight knowledge to the reader and focuses on how heavy metals impact humans and the environment, sources of heavy metals, current and especially removal methods using the MD method. Moreover, recent studies, challenges, and opportunities on MD membrane modules and heavy metal removal systems are discussed. More importantly, in this review, we have identified the gaps and opportunities that are required for enhancing the MD approach and its practical suitability for heavy metal removals. MD module and system showed high performance, proving their possible applications to remove heavy metal ions in water/wastewater treatment. Several methods have been devoted to separating or removing heavy metals from wastewater. Among them, membrane distillation (MD) has become one of the most attractive approaches due to its higher rejection rate than processes driven by pressure and lower energy consumption than traditional distillation processes. MD has gained significant attention for removing heavy metals than other techniques like ion exchange and adsorption in the last two decades. This review provides insight knowledge to the reader and focuses on how heavy metals impact humans and the environment, sources of heavy metals, and their removal methods using the MD method.
... After the following conclusion was reached, the differences in the pump of the freshwater generator affected the freshwater production efficiency positively by 39%, and changing the ejector positively affected the efficiency by 43.5%. Amaya-Vias et al. [36] have investigated the design of a simpler and less emissive desalination system. ey have stated that the direct Mathematical Problems in Engineering contact spray assisted evaporation method increased the potable water rate up to 34%, improving the microbubble method in distillation. ...
The process of desalination of seawater on commercial vessels is a vital event in the daily life of the crew. As a result of the rapid developments in ballast water treatment operations, the question of whether ballast water treatment systems can be used as the main desalination system in the daily life of the crew on commercial vessels has been raised. This study introduces the current desalination systems on commercial vessels and their evaluation criteria. According to the literature and our professional industrial research, there are three most suitable alternatives such as “freshwater generator,” “reverse osmosis method,” and “attaching additional membrane filter to mechanical and ultraviolet (UV) ballast water treatment system.” Similarly, the evaluation criteria are determined as “installation cost of the system,” “operational cost of the system,” “risk of the system polluting the environment,” “risk of the system harming the human health,” “ease of repair and maintenance of the system,” “ease of use of the system,” and “ease of installing the system on the ship.” Due to the need for field expertise, we conducted several rounds of expert consultations. The novelty of this study is twofold. First, we improved the intuitionistic fuzzy TOPSIS (IF-TOPSIS) method by extending an expert prioritization technique. We also used an intuitionistic fuzzy scale for the expert weights. Second, as far as we know, this is the first study that employs an improved IF-TOPSIS method for desalination systems on commercial vessels. Moreover, we compared the proposed method and other methods to analyze the results. Results show that “freshwater generator” is more promising than “attaching additional membrane filter to mechanical and UV ballast water treatment system” that is prior to “reverse osmosis method.” This study helps the users and authorities understand the evaluation and select the desalination systems.
... In addition, the possibility of using low-grade waste heat, which is widely abundant onboard ships, makes it a good candidate also for mobile maritime applications [9]. However, also in this field, the majority of studies focus on membrane distillation [10,11] or systems based on water-ammonia solutions [12], whereas AD is still under-exploited. Another significant advantage of AD over the other thermal methods commonly employed for desalination purposes [13], is the possibility of using low-grade heat, i.e. <90 • C and as low as 50 • C [14], which allows to use of waste heat already available in industrial sites or low-cost nonconcentrated solar collectors instead of concentrated solar power plants [15]. ...
Adsorption desalination (AD) is an emerging technology to reduce risk of freshwater scarcity, able to use renewable energy and applicable in decentralized areas. Only limited sorbents have been tested experimentally for AD systems. This study developed two composite sorbents based on LiCl as embedded salt and two matrices, namely, silica gel ([email protected]_30) and expanded vermiculite ([email protected]_45). The performed analysis figured out how the trade-off between high sorption capacity and good mass transfer caused by their different pore structures influences the desalination operations. The results were compared against a standard microporous Siogel. The sorption isobars indicated that the sorption behavior of [email protected]_30 is the combination of silica gel and the embedded LiCl crystals, while for [email protected]_45 is mainly the sorption process of the embedded LiCl crystals. [email protected]_45 reached the highest sorption capacity. The Dubinin-Astakhov equation described the equilibrium capacities of the sorbents. The kinetics coefficient (k) was employed to evaluate the sorption rate. Microporous Siogel showed the highest sorption rate, followed by [email protected]_30 and [email protected]_45. Finally, predicted specific daily water production (SDWP) were calculated, showing promising features for both [email protected]_30 and [email protected]_45, with [email protected]_30 achieving SDWP ranging from 43 to 60 m³/tonne/day) for the selected conditions.
... Due to the low operation temperature, various heat energies could be used in MD. In addition to the most convenient electric power supply, it can also come from renewable resources such as solar energy [233] and geothermal energy [234], as well as low-grade waste heat such as industrial waste heat [178] and ship waste heat [235]. ...
Water serves as an indispensable part of human life and production. On account of the overexploitation of traditional water sources, the demand for wastewater recycling is expanding rapidly. As a promising water treatment process, membrane distillation (MD) has been utilized in various wastewater treatments, such as desalination brine, textile wastewater, radioactive wastewater, and oily wastewater. This review summarized the investigation work applying MD in wastewater treatment, and the performance was comprehensively introduced. Moreover, the obstructions of industrialization, such as membrane fouling, membrane wetting, and high energy consumption, were discussed with the practical investigation. To cope with these problems, various strategies have been adopted to enhance MD performance, including coupling membrane processes and developing membranes with specific surface characteristics. In addition, the significance of nutrient recovery and waste heat utilization was indicated.
... The use of moderate temperatures (40-80°C) enables the use of residual heat sources from other operations or even renewable energy sources such as solar and geothermal energy [14]. This low energetic demand turns the process economically viable for large-scale purification and competitive with other membranebased separation processes like reverse osmosis and nanofiltration [15][16][17][18]. ...
Porous hydrophobic ceramic membranes have been increasingly applied in advanced membrane-based separation processes such as Direct Contact Membrane Distillation (DCMD) due to their higher chemical and mechanical resistances. The development of novel ceramic membranes enhanced with porosity is based on conventional techniques such as extrusion and tape casting, and unique processing such as dry-wet spinning and vacuum filtration. The relationships between shaping and surface hydrophobization related to the membrane structure, properties and performance of the ceramic membrane applied to DCMD are explained in this work. The manufacturing technique influences the membrane characteristics, and consequently the permeability in DCMD. Recent research is focused on manufacturing high porous hollow fibre ceramic membranes by dry-wet spinning. In contrast to the grafting of alkylsilanes, the chemical vapour deposition process has been applied as an effective surface modifying technique to enhance membrane hydrophobicity. Ceramic membranes are mostly applied to desalination in DCMD and have been little researched concerning the unique properties they can offer, such as superhydrophobicity and use in a harsh environment. In addition to the review of manufacturing techniques, polymer-derived ceramic (PDC) is proposed as a one-step ceramic membrane processing route for DCMD. Although only a handful of works addressed the use of PDC membranes applied to DCMD, the great potential of these materials is forecast.
... For large ships, distillation becomes a viable option, because instead of using expensive fuel or even worse, expensive electricity, to desalinate the water, much of the energy can come from recycled heat from the engines [50] [51]. The bigger the ship, the more heat is produced from its engines and the larger space it has to facilitate a small distillation plant onboard. ...
Climate change, urbanization and societal changes increase the prominence of water insecurity and sustainable urban water management is becoming a crucial challenge. In order to monitor and develop efficient policies the quantification of urban water performance is required, and the urban water metabolism approach can serve this goal.
This project examines patterns of water flows and evaluates water management performance by implementing a material flow analysis in Singapore and Hong Kong. Also, the technologies and economics of water reclamation from municipal wastewater focusing on direct use (drinking water) are evaluated. The feasibility of similar projects and comparison to alternatives such as desalination/imports from other regions are discussed as well.
... Thermal-driven desalination plants are the reference technologies to produce high quality freshwater onboard, as reported by Nemati et al. [27]. Among all desalination systems, the thermal desalination process obtained through multi-stage flash (MSF) distillation devices is the most frequently adopted, as reported through a comparative study by Amaya-Vías et al. [28]. They can be activated by engines waste heat with an average amount of thermal energy per unit of desalinized water of about 130 kWh t /m 3 , as demonstrated by Darawsheh et al. [29]. ...
To reduce the environmental impact of cruise ships, a crucial role is played by the
recovery of waste heat from diesel generators used to balance the onboard thermal
energy demand. To maximize the recovered waste heat, this paper proposes a novel
design methodology for ships energy systems based on the dynamic simulation
approach, suitably enhanced to consider moving objects. Through this approach,
partial load regimes due to variable energy requirements and the relative response of
innovative energy saving technologies are dynamically assessed by properly
considering real cruising conditions as a function of the ship position along its route. To
this aim, 3-D ship envelope models, detailed energy ship-plant system layouts, and
algorithms for deriving new customized hourly weather data files are developed in
MatLab and TRNSYS. To show the capability and potentials of the proposed
methodology, a novel case study referred to an LNG-powered cruise ship traveling in
the Norwegian fjords sea is presented. Different thermally and electrically activated
technologies are coupled in 16 energy ship-plant system layouts, implementing novel
controls strategies for optimizing the exploitation of the waste heat recoveries and cold-
ironing. Encouraging results are achieved for the best layout, including primary energy
savings of 18.1%, avoided pollutants emissions of 24.4 kt CO2 /y, 40.0 t NOx /y,
90.0 t SOx /y, 84.0 t PM2.5 /y, and a simple payback of 0.68 years. Finally, the
proposed methodology represents a step forward toward the modern early design of
onboard ship energy systems useful for ship designers, manufacturers, owners and
operators.
... A highly selective separation is observed by all configurations due to the sole presence of non-volatile salts, mainly sodium chloride, and as such each configuration is being considered at commercial scale [17][18][19][20]. Comparative assessments have subsequently centred on identifying the most energy efficient configuration and operating conditions [21][22][23][24]. In contrast, when applied to the recovery of volatile solutes, such as ammonia or volatile organic compounds, it is recognised that the selectivity of different membrane distillation configurations exhibit large variation dependent upon the specific operating conditions arising from the way the vapour pressure gradient is sustained [16,[25][26][27][28][29][30][31][32]. ...
Water recovery from concentrated blackwater has been studied using air gap (AGMD), direct contact (DCMD) and vacuum membrane distillation (VMD) to deliver decentralised sanitation. Whilst good water quality was achieved with each configuration, differences in the rejection of volatile compounds was observed. VMD exhibited the highest rejection of volatiles, specifically ammoniacal nitrogen, of all the configurations but fouling inhibited total flux. DCMD exhibited a temperature dependent volatile rejection which resulted in poor rejection at lower feed temperatures (≤ 40 °C). AGMD was identified as the most promising configuration for application within decentralised sanitation, since the rejection of volatiles was consistent over a range of operating temperatures with ammonia rejection directly related to solution pH. An increase in organic colloids and particles due to faecal contamination reduced COD removal due to the induction of wetting, but was shown to be offset by adoption of a smaller pore size (0.1 μm), and when complemented with upstream solid-liquid separation within a fully integrated system, will provide a robust sanitation solution. Importantly, this work has shown that AGMD can recover water from concentrated blackwater close to international discharge and reuse regulations in a single stage process; this is significant as blackwater consists of only urine and faeces, and is thus 40 times more concentrated than municipal sewage. It is proposed that the water quality produced reflects a step change to delivering safe sanitation, and is complemented by a simple method for heat recovery integration this is similarly advantageous for resource constrained environments common to decentralised sanitation solutions.
... The seawater desalination can be obtained by different technologies [20]: multi-stage flash (MSF) distillation; multi effect distillation (MED); membrane distillation (MD); reverse osmosis, (RO); electrodialysis (ED). Thermal activated desalination units can be a practical solution in large capacity passengers ships [21], and MSF is the most frequently adopted technology among the available ones [22]. MSF units are typically fed by the engines waste heat; the heat demand per unitary freshwater production ranges between 81 and 190 kWh t /m 3 , depending on the occurring number of system effects [23,24]. ...
Modern cruise ships are energivorous systems and their design is challenging due to stringent 11 restrictions on the environmental impact recently imposed by the International Maritime 12 Organization. Nowadays, energy saving technologies and strategies for ships can be selected and 13 analysed by means of system dynamic simulations. In this paper this innovative goal is obtained 14 through TRNSYS where the ship-envelope and the related energy system are modelled and simulated 15 by means of new customized weather data with the aim to optimize the system energy performance 16 by considering different objective function (maximum energy saving, minimum payback, etc.). To 17 show the effectiveness of the proposed approach, a novel case study is presented. It refers to a 18 modern cruise ship fuelled by liquified natural gas cruising in Mediterranean and Caribbean seas. 19 Novel hourly weather files are developed for accounting actual locations and orientations of the 20 moving ship. Low-, medium- and high-temperature engines waste heat recoveries are exploited for 21 supplying different thermally activated energy saving devices. Results of the conducted optimization 22 procedure show significant reductions of fuel consumption (between 0.1 and 1.9 kt/y), operating 23 costs (up to 615 k€/y), and pollutant emissions with respect to traditional systems. Short paybacks 24 are obtained (lower than 5 years), depending on the considered innovative system layouts. Finally, 25 useful design and operating criteria for ship manufacturers and users are provided.
... The advantage of MD is that it can treat huge amounts of oily wastewater generated during gas and oil extraction [19]. The possibility of using MD process under marine conditions was confirmed during studies performed with MD installation assembled on a ship [28]. ...
Oily wastewaters constitute a dangerous pollution to the natural environment; hence, new methods of their treatment are constantly being developed. Bilge water generated on ships is an important pollutant for marine environment. In addition to oil, these wastewaters often contain a variety of harmful constituents, such as surfactants and heavy metals. In this work membrane distillation was used for the treatment of bilge water, resulting in almost the complete separation of pollutants. However, the organic matter present in bilge water can cause the wetting of hydrophobic membranes. Polypropylene membranes were applied and their good resistance for wetting was confirmed during long-term studies of separation of bilge water with different compositions. It was observed that a significant amount of precipitate containing CaCO3 was formed on the membrane surfaces as a result of feed heating, resulting in decline of the permeate flux. The initial module efficiency was restored using a periodic rinsing of the membranes with a diluted HCl solution. Tested bilge water contained a significant amount of SO4⁻² ions (592–1388 mg/L). The formation of precipitate also containing CaSO4 was observed after the feed was concentrated to 2.72 g SO4⁻²/L. As a result of deposit precipitation, the concentration of SO4⁻² ions was decreased to 1.52 g/L, which allowed to continue the bilge water separation process without the permeate flux decline.
Seawater desalination is one of the most widely used technologies for freshwater production; however, its high energy consumption remains a pressing global challenge. Both the development and utilization of sustainable energy sources are anticipated to mitigate the energy shortages associated with seawater desalination while also effectively addressing the environmental issues linked to fossil fuel usage. This study provides a comprehensive overview of the classification and evolution of traditional desalination technologies, emphasizing the advancements, progress, and challenges associated with integrating various sustainable energy sources into the desalination process. Then, the cost, efficiency, and energy consumption of desalination systems driven by sustainable energy are discussed, and it is found that even the most widely used reverse osmosis (RO) technology driven by fossil fuels has CO2 emissions of 0.3–1.7 kgCO2/m3 and the lowest cost of desalinated water as high as 0.01 USD/m3, suggesting the necessity and urgency of applying sustainable energy. A comparison of different seawater desalination systems driven by different sustainable energy sources is also carried out. The results reveal that although the seawater desalination system driven by sustainable energy has a lower efficiency and a higher cost than the traditional system, it has more potential from the perspective of environmental protection and sustainable development. Furthermore, the efficiency and cost of desalination technology driven by a single sustainable energy source is lower than that driven by multi-sustainable energy sources, while the efficiency of desalination systems driven by multi-sustainable energy is lower than that driven by hybrid energy, and its cost is higher than that of desalination systems driven by hybrid energy. Considering factors such as cost, efficiency, consumption, economic scale, and environmental impact, the integration of various seawater desalination technologies and various energy sources is still the most effective strategy to solve water shortage, the energy crisis, and environmental pollution at present and in the future.
There is an urgent need for the development of new water resources in order to solve the problem of the world’s growing demand for clean water. Membrane distillation (MD) is a promising alternative to conventional seawater desalination. Although MD itself is often defined as sustainable desalination technology, there are many aspects within the membrane manufacture and process operation that make it far from being green. For instance, non-biodegradable polymers, toxic solvents and fluoroalkyl silanes are typical chemicals that unfortunately are used in membrane fabrication protocols. Additionally, the huge amount of wastewater generated from membrane fabrication processes makes solvent-free methods more attractive and desirable for extensive investigation. Apart from this, the low energy efficiency of the MD process can be effectively overcome by integrating MD systems with low-grade waste heat. This review critically addresses and discusses the recent advances in methods and strategies to improve the sustainability of MD technology, which is not a common scope of study among the research community. Here, our attention has been devoted to the main aspects of MD membrane fabrication, such as polymers, solvents (and their costs), nonsolvents, additives, solvent-free fabrication procedures, fluoro-free post-modification, and MD operation (energy consumption). This review intends to introduce inspiration for membrane scientists for the development of the next-generation MD process, by promoting the sustainable transformation of today’s approaches into a greener way. In this latter scenario, we provide some timely considerations that could be followed by the researchers in the field.
A comprehensive review of water desalination systems powered by renewable energy. • The importance of combination of solar energy with hybrid desalination systems. • Renewable energy integration with different desalination techniques. • A comparative analysis of integration of renewable energy with hybrid desalination. • Challenges and future recommendations for successful integration of renewable energy with desalination. This paper offers a comprehensive overview of advanced water desalination systems powered by renewable energy sources, specifically focusing on developments in the past decade. Solar energy is particularly emphasized as a pivotal resource for powering diverse desalination methods, including membrane distillation, reverse osmosis, humidification-dehumidification, forward osmosis, and hybrid systems. The primary objectives of this study encompass evaluating current advancements in renewable energy systems, especially solar energy, for driving water desalination processes. Furthermore, the study aims to identify gaps in research, challenges, and recommendations within these processes, and to assess the performance and refinement potential of hybrid desalination systems. Through a comprehensive analysis of various investigations, integrated effectiveness and cost-efficiency are examined, focusing on practical energy utilization. Notably, the analysis reveals the potential of hybrid desalination systems to reduce energy consumption. For instance, the hybridization of forward osmosis with membrane distillation showcases a significant energy ratio decrease from 0.89 to 0.64. Moreover, the combination of humidification-dehumidification with reverse osmosis is shown to reduce energy usage while enhancing freshwater output by up to 38% compared to standalone reverse osmosis. However, challenges persist, such as the need for improved integration of hybrid systems with concentrated solar collectors like photovoltaic thermal and concentrated photovoltaic thermal technologies.
Membrane distillation (MD) is a promising process for high-quality water reclamation mainly due to its high capacity to retain non-volatile components and operate without the need for hydraulic pressure. However, its low energy efficiency limits its widespread use. With that in mind, this paper critically summarizes the different engineered configurations of membrane distillation coupled with renewable energy sources and waste heat, namely: solar, geothermal, and waste heat, to overcome the limitations associated with low energy efficiency commonly reported. From all sources, solar-driven processes are preferred due to the greater technological maturity related to flat plate collectors (FPCs), evacuated tube collectors (ETCs), compound parabolic concen-trators (CPCs), salt-gradient solar ponds (SGSPs), and solar stills. The integration with renewable energy sources represents one of the leading solutions for energy consumption, proving to be a decisive choice for the system's economic viability. The summarized studies suggest membrane distillation's potential to be economically competitive with the classical membrane separation process (ultrafiltration, nanofiltration, and reverse osmosis) when waste heat is considered for wastewater treatment. Even under these conditions, alternative energy sources have a few shortcomings to be investigated in future studies, such as short periods of solar radiation and the intermittence of waste heat sources. These factors still represent obstacles to an uninterrupted and large-scale operation of membrane distillation and must be overcome in a near future. Even so, successful case studies on full-scale systems that integrate membrane distillation and solar energy sources suggest the process's potential for widespread use in the near term.
With growing demand for freshwater resources, membrane distillation (MD) attracts intensive attention owing to the possibility of reclaiming almost 100% freshwater with superhydrophobic membranes as the pivotal separation units. Current superhydrophobic membrane still suffers relatively complex preparation process and limited membrane flux. Herein, we developed a promising route to fabricate a high-flux superhydrophobic poly(vinylidene fluoride) (PVDF) membrane by a simple solute and solvent co-crystallization (SSCC) method, which endowed the membrane ultra-high porosity and flux. We also found that the pore size of superhydrophobic membrane can be adjusted by controlling the crystallization process of DMSO, which gave rise to membrane higher flexibility. The membrane exhibited the outperforming desalination performance even in multiple harsh environments including different temperature, salty concentration, and pH, with/without humic acid. The membrane also displayed distinguished anti-fouling performance and long-term stability, which is quite significant for practical application.
Membrane distillation (MD) is a sustainable approach for the treatment of challenging saline water by effective removal of non-volatile compounds at high water recovery, offering near-to-zero liquid discharge to environment. Progressive efforts have been made in recent literature to mitigate membrane fouling and enhance the wetting resistance of MD for long-term stable operation; however, extensive energy consumption is the key constraint that hinders MD to become an economically sustainable solution for industrialization. This review represents the evaluation of energy consumption in MD in comparison with other existing advanced water treatment technologies (e.g., reverse osmosis). An up-to-date review of low-energy MD utilization to minimize energy consumption is provided in this work. High energy consumption in MD can be compensated by the effective utilization of renewable energy sources such as solar energy, geothermal energy, or waste heat. However, due to the sporadically unequal distribution and unstable availability of these low-grade sources, the dependence on the abundance of these energy sources may limit the flexibility in commercial MD applications. A recent approach to reduce specific thermal energy through direct heating of the membrane or spacer is also discussed in this review. The development of the membrane materials/configurations was highlighted for mitigating the effects of temperature polarization and improving energy efficiency by localized heating at/near the membrane surface by using photothermal, electrothermal, or induction materials.
In the global effort to reduce Green House Gases and carbon emissions, there is great importance for the shipping industry to decarbonise and move forward into a greener future. However, there is a lack of academic commentary on how attempts at various decarbonisation methods reported in research articles have developed over the 21st century, particularly in line with the relevant policy and regulatory developments. This paper analyses how the shipping industry has decarbonised by utilising 294 papers from 2000 to 2020. By analysing 20 years’ worth of research, this paper delivers a comprehensive review of shipping decarbonisation research and analyses the evolution of its themes as a function of time. It therefore aids to develop a greater understanding and comparison of governmental, economic and academic perspectives (and their potential alignment) for the industry to decarbonise. For 2017–20 the key shipping decarbonisation technologies were summarised and their advantages, disadvantages and current academic literature applications are revealed. Furthermore, the analysis of the evolution of shipping decarbonisation research themes reveals clear research gaps in the current literature and guides the development of a future research agenda with the prediction of future opportunities and potential for shipping decarbonisation research developments for the shipping industry.
Due to the laminar structure constructed by two-dimensional nanosheets, nanochannels are formed in the graphene oxide membrane (GOM), including capillaries formed by two closely spaced graphene sheets and nanopores in the nanosheets. These nanochannels have strong molecular sieving properties that can be tuned by various methods and applied in molecules separation. Such membranes are often used for the separation of different molecules or ions, but are rarely used for the isotope separation. In this work, superhydrophobic modification of the GOM was achieved by introducing layers of fluorinated silica nanoparticles on the membrane surface, combining the fluoro-containing resin to enhance the adhesion and decrease the surface energy. Using light/heavy water as a model, the hydrogen isotopic separating performance of this composite membrane was evaluated in an air gap membrane distillation (AGMD) apparatus. It was shown that the superhydrophobic coating of the membrane can effectively prevent the liquid water penetrating into the membrane, thus providing a pure vapor process in the membrane. Meanwhile, when compared to pure GOM and commercial polymeric membranes, the resultant membranes acquired superior isotopic selectivity in membrane distillation. The best performing membrane contains three layers of nanoparticles, of which the outermost surface was treated with 40 μL (heptadecafluoro-1, 1, 2, 2-tetrahydrodecyl) trimethoxysilane (17-FTMS) and 10 μL methyltrimethoxysilane (MTMOS). A mean separation factor value of 1.151 and a permeation flux of 0.036 kg m⁻² h⁻¹ were obtained. In addition, continuous test for up to 90 h showed a stable performance of the composite membrane, without compromising the selectivity and flux of the membrane. This study not only demonstrates the potential of superhydrophobic composite GOM for hydrogen isotopic sieving in membrane distillation, but also provides a facile and generic method for superhydrophobic modification of the hydrophilic membrane.
This article presents a literature review of solid waste management on cruise ships using a bibliographic search of the main databases. Articles that discuss waste management were spread over different research areas, demonstrating that the topic is cross-sectional and interconnected, involving social, economic and political considerations. The text is organized into four topics: generation, treatment, disposal and impacts. Recent years have seen increasing interest in cruise ship waste management, likely due to the growing tourism market, with an annual increase of 7.4% in the number of passengers between 1990 and 2018. However, this growth may aggravate environmental, social and economic impacts, making it essential to promote research and studies in the area.
Purpose
The purpose of this paper is to review maintenance practices, tools and parameters for marine mechanical systems that can be classified as plant, machinery and equipment (PME). It provides an insight for the maintenance crew on which maintenance parameters and practices are critical for a given PME systems.
Design/methodology/approach
The review paper characterizes the various maintenance parameters and maintenance practices used onshore and offshore for PME and identifies the possible gaps.
Findings
A variety of maintenance techniques are being used in the marine industry such as corrective maintenance, preventive maintenance and condition-based maintenance. As marine vehicles (MV) get older, the most important maintenance parameters become maintenance costs, reliability and safety. Maintenance models that have been developed in line with marine mechanical systems have been validated using a single system, whose outcome could be different if another PME system is used for validation.
Research limitations/implications
There is a limited literature on MV maintenance parameters and maintenance characterization regarding mechanical systems. The maintenance practices or strategies of marine mechanical systems should be based on maintenance parameters that suit the marine industry for a given PME.
Originality/value
Based on the available literature, the paper provides a variety of maintenance framework, parameters and practices for marine mechanical systems. The paper further gives an insight on what maintenance parameters, strategies and platforms are given preference in the shipping industry.
Membrane-Distillation in Desalination is an attempt to provide the latest knowledge, state of the art and demystify outstanding issues that delay the deployment of the technology on a large scale.
It includes new updates and comprehensive coverage of the fundamentals of membrane distillation technology and explains the energy advantage of membrane distillation for desalination when compared to traditional techniques such as thermal or reverse osmosis.
The book includes the latest pilot test results from around the world on membrane distillation desalination.
Water pollution by metals and, in particular, acid mine drainage (AMD) is one of the most severe environmental problems to be faced by society. In this sense, treatment by membrane processes is a promising alternative, highlighting membrane distillation (MD) features to overcome the limitations of conventional processes. In this work, water gap MD (WGMD) and air gap MD (AGMD) were tested under different feed temperatures and organic matter concentrations, using 0.45 μm polytetrafluoroethylene (PTFE) membranes and real AMD from Tinto River, which is located in SW Spain.
For both MD modes, high permeate fluxes (up to 16.80 L h⁻¹ m⁻² for WGMD and 10.16 L h⁻¹ m⁻² for AGMD) were reached and over 99% rejection was obtained for electrical conductivity, ions and metals (Na⁺, K⁺, Ca²⁺, Mg²⁺, F⁻, Cl⁻, NO3⁻, SO4²⁻, Cu, Fe, Zn, Cd, Co, Mn, Ni). In addition, specific thermal energy consumption (STEC) per unit of permeate water was calculated to obtain MD heat requirements. Furthermore, MD efficiency in terms of heat recovery was estimated by gained output ratio (GOR) between useful and total heat of the system. On that basis, MD and specifically the WGMD mode, showed great potential for the sustainable treatment of AMD.
This paper presents the design and experimental analysis of a thermal water pump coupled with a reverse osmosis desalination membrane. The operation, thermodynamic cycle and design of the proposed system are explained with the aid of system schematics and thermodynamic process diagrams, while the experimental performance of the thermal water pump in combination with a reverse osmosis membrane is presented and discussed. It is shown that for feed water at a salt concentration of 1184 ppm and a heat source temperature of 86 °C, the proposed system is shown to be able to produce fresh water at a rate of 1.27 L/h with a specific energy consumption of 165 MJ/m³. The recovery ratio obtained under these conditions is shown to be 26%. The performance and characteristics of the proposed system are contrasted with data for existing multi-stage thermal desalination systems as well as Rankine cycle–reverse osmosis desalination systems and it is shown to compare favourably to both for low salinity applications.
Thermal-energy-driven desalination processes such as membrane distillation (MD), humidification dehumidification (HDH), and multi-stage flash (MSF) can be used to concentrate water up to saturation, but are restricted to low per-pass recovery values. High recovery can be achieved in MD through feed recirculation. In this study, several recirculation strategies, namely batch, semibatch, continuous, and multistage, are compared and ranked based on flux and energy efficiency, which together influence overall cost. Batch has higher energy efficiency at a given flux than semibatch and continuous recirculation because it spends more operating time treating lower salinity water for the same value of overall recovery ratio. Multi-stage recirculation is a steady-state process that can approach batch-like performance, but only with a large number of stages. Feed salinity rises during the batch operating cycle, and as a result feed velocity may have to be increased to avoid operating above the critical specific area wherein both GOR and flux are low due to significant heat conduction loss through the membrane. Finally, the choice of optimal membrane thickness for batch operation is compared to that of continuous recirculation MD.
Various membrane separation processes are being used for seawater desalination and treatment of wastewaters in order to deal with the worldwide water shortage problem. Different types of membranes of distinct morphologies, structures and physico-chemical characteristics are employed. Among the considered membrane technologies, membrane distillation (MD), osmotic distillation (OD) and osmotic membrane distillation (OMD) use porous and hydrophobic membranes for production of distilled water and/or concentration of wastewaters for recovery and recycling of valuable compounds. However, the efficiency of these technologies is hampered by fouling phenomena. This refers to the accumulation of organic/inorganic deposits including biological matter on the membrane surface and/or in the membrane pores. Fouling in MD, OD and OMD differs from that observed in electric and pressure-driven membrane processes such electrodialysis (ED), membrane capacitive deionization (MCD), reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), etc. Other than pore blockage, fouling in MD, OD and OMD increases the risk of membrane pores wetting and reduces therefore the quantity and quality of the produced water or the concentration efficiency of the process. This review deals with the observed fouling phenomena in MD, OD and OMD. It highlights different detected fouling types (organic fouling, inorganic fouling and biofouling), fouling characterization techniques as well as various methods of fouling reduction including pretreatment, membrane modification, membrane cleaning and antiscalants application.
Membrane distillation (MD) has shown potential as a means of desalination and water purification. As a thermally driven membrane technology which runs at relatively low pressure, which can withstand high salinity feed streams, and which is potentially more resistant to fouling, MD could be used for desalination where reverse osmosis is not a good option. The use of thermal energy, rather than electrical energy, and the fact that MD membranes can withstand dryout make this technology attractive for renewable power applications as well. However, most research on MD has focused on maximizing membrane flux as opposed to minimizing energy consumption and cost, and current MD systems suffer from poor energy efficiency compared to other desalination systems. In solar driven systems, the reported thermal performance has not been much better than a simple solar still. This paper examines the energy efficiency of single-stage MD-based desalination cycles in each of the MD configurations commonly used for desalination (direct contact, air gap, and vacuum) and compares the gained output ratio, or GOR, of each configuration across the range of membrane module geometries, and operating conditions. Limitations of each configuration are identified. Direct contact MD and air gap MD, in particular, have potential for high GOR.
Hydrophobic membranes are perceived to be chemically stable and resistant to dry-out during intermittent membrane distillation (MD) operations. However, distillate quality deterioration has been reported in field tests of solar-powered MD systems. This work investigates the effects of salt deposition, resulting from membrane dry-out, on the properties of two types of commercial hydrophobic membranes commonly used for MD purposes. The membranes are made of polytetrafluoroethylene (PTFE) and polyvinylidenefluoride (PVDF). The intermittent operation was simulated by a series of wet/dry cycles using seawater at MD operational temperatures. Membrane properties including surface contact angle, gas permeability, and mechanical strength were assessed, along with other structural characteristics like pore size distribution. The morphology of the salt-exposed membranes was also investigated using SEM and EDS. Atomic force microscopy (AFM) measurements were carried out to assess surface morphology and quantify surface roughness, in relation to the fouling process. AFM was combined with the use of a CaCO3 colloid probe to assess adhesion forces between CaCO3 and the membranes. DCMD experiments were conducted to study the post-fouling performance of the membranes in the MD process. Significant scaling was detected starting from the first week of seawater exposure, as evidenced by all the characterization techniques used. PVDF and PTFE membranes were observed to behave somewhat differently under these fouling conditions. DCMD experiments proved that membrane wetting was exacerbated by intermittent operation.
Membrane Distillation (MD) is a thermally-driven separation process, in which only vapour molecules transfer through a microporous hydrophobic membrane. The driving force in the MD process is the vapour pressure difference induced by the temperature difference across the hydrophobic membrane. This process has various applications, such as desalination, wastewater treatment and in the food industry.This review addresses membrane characteristics, membrane-related heat and mass transfer concepts, fouling and the effects of operating condition. State of the art research results in these different areas will be presented and discussed.
Membrane distillation is a process that utilizes differences in vapor pressure to permeate water through a macro-porous membrane and reject other non-volatile constituents present in the influent water. This review considers the fundamental heat and mass transfer processes in membrane distillation, recent advances in membrane technology, module configurations, and the applications and economics of membrane distillation, and identifies areas that may lead to technological improvements in membrane distillation as well as the application characteristics required for commercial deployment.
A detailed mathematical model, based on mass and energy balances, was developed in order to provide guide lines for the optimal design and operation of a vacuum-multi-effect membrane distillation system. Since there is no well-established solution for the V-MEMD system, two case studies were used for the feed channel. The comparison between experimental and theoretical values of distillate flux showed low deviations (1.9%–11.1%) for tap water as regards the second case study. However, the deviations were higher, in the range of 2%–23%, when saline water was used as feed solution. The model was also utilized to investigate the effect of the operating conditions, membrane structural properties and design parameters on the performance indicators. High values of the hot water inlet temperature and feed inlet temperature lead to increase of water productivity and recovery ratio. Membranes with high porosity, large pore size and low thickness are the best candidates for enhancing the water productivity. Introduction of spacer improves the mass and heat transfer in the channels of the system. Also, the increment of the number of effects from 2 to 4 significantly lowers the specific thermal energy consumption.
This work presents a steady-state thermodynamic model for absorption refrigeration cycles with water-LiBr and ammonia-water working pairs for purpose of application on a ship. The coefficient of performance was studied with different generator and evaporator temperatures in ISO and tropical conditions. Absorption refrigeration systems were examined using exhaust gases, jacket water, and scavenge air as energy sources. Optimal generator temperatures for different refrigerant temperatures were found using different waste heat sources and for the absorption cycle itself. Critical temperature values (where the refrigeration power drops to zero) were defined. All of these values were used in order to evaluate the cooling power and energy production possibilities in a bulk carrier. The process data of exhaust gases and cooling water flows in two different climate conditions (ISO and tropical) and operation profiles of a B. Delta37 bulk carrier were used as initial data in the study. With the case ship data, a theoretical potential of saving of 70% of the electricity used in accommodation (AC use) compressor in ISO conditions and 61% in tropical conditions was recognized. Those estimates enable between 47 and 95 tons of annual fuel savings, respectively. Moreover, jacket water heat recovery with a water-LiBr system has the potential to provide 2.2–4.0 times more cooling power than required during sea-time operations in ISO conditions, depending on the main engine load.
Three major cruise lines account for 82% of the total market share. Their financial statements show different results between the operating incomes and net incomes over time. To examine the major causes of the differences, this study measured the efficiency of the top three cruise lines to develop a network DEA model to analyze the cruise operations at two stages, namely operating and non-operating stages. In addition, the determinants of the efficiencies were examined using a bootstrapped-truncated regression model. Overall, cruise lines were efficient at the operating stage, but varied widely in the efficiency of the non-operating stage. Cruise lines attempting high capacity expansion were relatively inefficient because of the heavy interest payments arising from the high debt-to-capital ratio. Moreover, the neglected hedging policy regarding the financial risks also contributed to the inefficiency.
Given increasing regional water scarcity and that almost half of the world's population lives within 100 km of an ocean, seawater represents a virtually infinite water resource. However, its exploitation is presently limited by the significant specific energy consumption (kWh/m³) required by conventional desalination technologies, further exasperated by high unit costs ($/m³) and environmental impacts including GHG emissions (g CO2-eq/m³), organism impingement/entrainment through intakes, and brine disposal through outfalls. This paper explores the state-of-the-art in present seawater desalination practice, emphasizing membrane-based technologies, while identifying future opportunities in step improvements to conventional technologies and development of emerging, potentially disruptive, technologies through advances in material science, process engineering, and system integration. In this paper, seawater reverse osmosis (RO) serves as the baseline conventional technology. The discussion extends beyond desalting processes into membrane-based salinity gradient energy production processes, which can provide an energy offset to desalination process energy requirements. The future membrane landscape in membrane-based desalination and salinity gradient energy is projected to include ultrahigh permeability RO membranes, renewable-energy driven desalination, and emerging processes including closed-circuit RO, membrane distillation, forward osmosis, pressure retarded osmosis, and reverse electrodialysis according various niche applications and/or hybrids, operating separately or in conjunction with RO.
An experimental study is used to examine the effect of high concentration of several salts, i.e., NaCl, MgCl2, Na2CO3 and Na2SO4 on permeate flux and rejection factor by air gap membrane distillation (AGMD). A comparative study involving three different membrane pore sizes (0.2, 0.45 and 1.0μm) were performed to investigate the influence of pore size on energy consumption, permeate flux and rejection factor. The permeate flux decline is higher than that predicted from the vapour pressure reduction. Furthermore, the energy consumption was monitored at different membrane pore size and was found to be increased when the concentration increased.
Membrane scaling and mitigation techniques during air gap membrane distillation (AGMD) of seawater were investigated. The results showed a strong influence of AGMD operating temperature on not only the process water flux but also membrane scaling and subsequent cleaning efficiency. Elevating feed/coolant temperature from 35/25 to 60/50 °C increased water flux, but also escalated membrane scaling of the AGMD process. Membrane scaling was more severe, and occurred at a lower water recovery (68%) when operating at 60/50 °C compared to 35/25 °C (78%) due to increased concentration polarisation effect. Operating temperature also affected the efficiency of the subsequent membrane cleaning. Membrane scaling that occurred at low temperature (i.e. 35/25 °C) was more efficiently cleaned than at high temperature (i.e. 60/50 °C). In addition, membrane cleaning using vinegar was much more efficient than fresh water. Nevertheless, vinegar cleaning could not completely restore the membrane surface to the original condition. Scaling material remaining on the membrane surface facilitated scaling in the next operation cycle. On the other hand, anti-scalant addition could effectively control scaling. Membrane scaling during AGMD of seawater at 70% water recovery and 60/50 °C was effectively controlled by anti-scalant addition.
This study aimed to optimise an air gap membrane distillation (AGMD) system for seawater desalination with respect to distillate production as well as thermal and electrical energy consumption. Pilot evaluation data shows a notable influence of evaporator inlet temperature and water circulation rate on process performance. An increase in both distillate production rate and energy efficiency could be obtained by increasing the evaporator inlet temperature. On the other hand, there was a trade-off between the distillate production rate and energy efficiency when the water circulation rate varied. Increasing the water circulation rate resulted in an improvement in the distillate production rate, but also an increase in both specific thermal and electrical energy consumption. Given the small driving force used in the pilot AGMD, discernible impact of feed salinity on process performance could be observed, while the effects of temperature and concentration polarisation were small. At the optimum operating conditions identified in this study, a stable AGMD operation for seawater desalination could be achieved with specific thermal and electrical energy consumption of 90 and 0.13 kW h/m3, respectively. These values demonstrate the commercial viability of AGMD for small-scale and off-grid seawater desalination where solar thermal or low-grade heat sources are readily available.
Direct contact membrane distillation (DCMD) supplied with waste heat was demonstrated for water recovery from saline demineralisation regeneration waste. The pilot plant was located at a gas fired power station which provided the < 40 °C waste heat and wastewater to the DCMD system with 0.67 m2 of membrane area. The trial was operated over three months without replacing the membranes or module and achieved 92.8% water recovery. Flux was approximately 3 L/(m2·h) and was dependant mostly on the waste heat temperature being supplied. Membrane fouling affected flux and thermal energy demand only at the very end of the trial. The system produced a high quality distillate product with average 99.9% dissolved solids rejection. Small amounts of ammonia and carbon dioxide however were found in the permeate. Membrane analysis post-trial revealed fouling was principally inorganic scale but organic matter on the membrane was also evident. Permeate side fouling was also observed, attributed to corrosion of the cooling heat exchanger. Based on the available energy for a continuously operating 500 MW (electric) rated power station, the treatment potential was estimated at up to 8000 kL/day, which is practical for supplying water to numerous industrial, residential or agricultural sites.
Membrane distillation (MD) has gained significant regard from industrial and academic perspective in recent years, thus the frequency of publications related to the field has greatly accelerated. New perspectives have boosted the research activities related to deeper understanding of heat and mass transport phenomenon, novel applications and fabrication of the membranes specifically designed for MD. New efforts for module fabrication and understanding and control of non-traditional fouling in MD have also been highlighted in the recent literature. The current review summarizes the important and interesting recent developments in MD from the perspectives of membrane fabrication, heat and mass transport phenomenon, nontraditional fouling, module fabrication and applications. The future research directions of interest have also been pointed out.
In this work, we first show the findings of the autopsy performed on the membranes used in the
Scarab AB ® membrane distillation (MD) system at the solar MD pilot plant in Plataforma Solar
de Almeria (PSA) in Spain. The fouling and the damage endured by the MD membranes during
intermittent long-term (2010-2013) solar-powered operation in the pilot plant were assessed and
characterized. Different cleaning strategies were used to remove the fouling layer and restore the
membrane properties. Data regarding relevant membrane characteristics for the MD process,
such as; contact angle, gas permeability, porosity, liquid entry pressure, mechanical strength,
etc., and their relationship with the membrane performance under MD operation were discussed
and analyzed. Scanning electron microscopy (SEM) was employed to study the morphology of
the fouled and cleaned membranes and characterize the membrane damage. The identified best
cleaning procedure was then applied in the MD plant system at PSA. Results suggested that
cleaning effectively removed great part of the fouling and reduced the wetting of the membranes.
However, this improvement was offset by the effect of inactive periods during which wetting
processes were favored.
The demand of freshwater has surpassed the renewable limit and new water sources are associated with an intensive use of energy. Coincidence between scarcity of water and availability of solar radiation makes solar energy the most suitable option to mitigate the water deficit. This paper analyzes the use of energy for decentralized water production using membrane desalination systems fed with solar energy. An analysis is performed based on experimental results from the most advanced commercial prototypes of different technologies of membrane distillation using various configurations, i.e., air-gap, permeate-gap and vacuum; with flat-plate and spiral-wound membranes. The systems operate with thermal energy, although there is some electrical consumption for pumping and in some cases for sustaining vacuum. The thermal energy requirements per unit volume of water produced are assessed in each case, considering the effect of different operational conditions like the temperature regime and the salinity of the input water.
The flux performance of different hydrophobic microporous flat sheet commercial membranes made of poly tetrafluoroethylene (PTFE) and poly propylene (PP) was tested for Red Sea water desalination using the direct contact membrane distillation (DCMD) process, under bench scale (high ΔT) and large scale module (low ΔT) operating conditions. Membranes were characterized for their surface morphology, water contact angle, thickness, porosity, pore size and pore size distribution. The DCMD process performance was optimized using a locally designed and fabricated module aiming to maximize the flux at different levels of operating parameters, mainly feed water and coolant inlet temperatures at different temperature difference across the membrane (ΔT). Water vapor flux of 88.8 kg/m2h was obtained using a PTFE membrane at high ΔT (60 °C). In addition, the flux performance was compared to the first generation of a new locally synthesized and fabricated membrane made of a different class of polymer under the same conditions. A total salt rejection of 99.99% and boron rejection of 99.41% were achieved under the extreme operating conditions. On the other hand, a detailed water characterization revealed that low molecular weight non-ionic molecules (ppb level) were transported with the water vapor molecules through the membrane structure. The membrane which provided the highest flux was then tested under large scale module operating conditions. The average flux of the latter study (low ΔT) was found to be eight times lower than that of the bench scale (high ΔT) operating conditions.
A new module design for membrane distillation, namely material gap membrane distillation (MGMD), for seawater desalination has been proposed and successfully tested. It has been observed that employing appropriate materials between the membrane and the condensation plate in an air gap membrane distillation (AGMD) module enhanced the water vapor flux significantly. An increase in the water vapor flux of about 200–800% was observed by filling the gap with sand and DI water at various feed water temperatures. However, insulating materials such as polypropylene and polyurethane have no effect on the water vapor flux. The influence of material thickness and characteristics has also been investigated in this study. An increase in the water gap width from 9 mm to 13 mm increases the water vapor flux. An investigation on an AGMD and MGMD performance comparison, carried out using two different commercial membranes provided by different manufacturers, is also reported in this paper.
http://www.sciencedirect.com/science/article/pii/S0376738813006595
Desalination technologies improve water quality, greatly reduce water shortage problems, and improve quality of life and economic status. Two main technologies are currently used in water desalination: thermal (phase-change) processes and membrane processes. The primary thermal distillation processes include multistage flash distillation (MSF), multi-effect distillation (MED), and vapor compression (VC). The VC process encompasses two types: mechanical (MVC) and thermal (TVC). The common membrane desalination processes include reverse osmosis (RO) and electrodialysis (ED and EDR).
Membrane distillation (MD) is an alternative technology for the separation of mixtures through porous hydrophobic membranes. A commercially available PTFE (polytetrafluoroethylene) membrane was used in direct contact membrane distillation (DCMD) to investigate the effect of module dimensions on performance. Membrane properties, such as liquid entry pressure (LEP), contact angle (CA), pore diameter, effective porosity and pore size distribution, were characterized and used in analysis. A two dimensional (2D) model containing mass, energy, and momentum balance was developed for predicting permeate flux production. Different flow modes including co-current and counter-current flow mode were studied. The effect of linear velocity on permeation flux for both wide and short, and long and narrow module designs was investigated. The mass transfer coefficients for each condition were calculated for comparison of the module designs. The effects of operating parameters such as flow mode, temperature difference, and NaCl concentration were also considered. The simulated results were validated by comparing with experimental results. Good agreement was found between the numerical simulation and the experiments.
In this paper, field performance of a small-scale seawater reverse osmosis unit installed in Urla Bay-Izmir, Turkey was analyzed and presented. The design of SWRO system in Urla consists of two types of FilmTec polyamide thin film composite spiral wound seawater reverse osmosis membranes (high rejection FILMTEC XUS SW30XHR-2540 RO membrane and FILMTEC SW30-2540 RO membrane) which could be operated in parallel. To make a comparative study between two types of membranes regarding their desalination performances and boron rejections, each membrane was operated individually for each set of experiments. This comparison was made via investigation of the effects of feed seawater temperature (10–16°C), operating pressure (55, 60 and 62bar), and pH adjustment on the feed side (pH 7.0–7.5).
Membrane distillation (MD), a thermally-driven membrane separation process has been widely studied in recent years and the membrane properties are known to have significant effect on the performance of the MD process. This paper studied the microstructure of PTFE membranes from three different sources for MD application. The parameters investigated include pore size, thickness, porosity and tortuosity. Non-supported membranes were also tested for comparison. The experimental results for different pore size, thickness, porosity, tortuosity and support materials in direct contact membrane distillation (DCMD) were compared with the theoretical flux simulated from the Schofield model using Polymath NLE solver. The temperature polarisation coefficient was also determined to establish the relationship between the membrane microstructure and performance. The results indicated that the structure and porosity of support materials play important roles in determining the performance of DCMD. Higher fluxes and lower temperature polarisations were observed over membranes with large pore size, low thickness, high porosity and low tortuosity. Membrane porosity, pore size and the presence of support materials were found to have significant effects on flux and temperature polarisation.
Air Gap Membrane Distillation, using a high concentration of NaCl, MgCl2, Na2CO3, and Na2SO4, is implemented in this study. Permeate fluxes are measured for different feed concentrations and membrane pore sizes (0.2 and 0.45μm). The flux declines as the concentration of salt increases, and increases as the pore size increases. The TF200 membrane showed excellent hydrophobicity compared to TF450. Moreover, the energy consumption was measured at different salt concentrations for the different membrane sizes, and was found to be independent of membrane pore size, salt type and salt concentration in the feed solution.
This paper presents a comprehensive review and assessment of desalination technologies such as thermal which includes multi-stage flash (MSF) and multiple effect distillation (MED), membrane reverse osmosis (RO), and hybrid (MSF/MED-RO). The assessment includes energy requirements, water production cost, technology growth trends, environmental impact and potential for the technology improvements. Comparison and technology matrix of commercial technologies are highlighted. The global desalination policies for the major desalination user countries, Kingdom of Saudi Arabia (KSA), United States of America (USA), Spain, China and Kuwait are given. More detailed analysis of desalination, cogeneration, and water situation in the United Arab Emirates (UAE) with some related recommendations for future policy and plans are also presented.
The main objective of this work was to investigate boron removal from seawater using two commercial high rejection SWRO membranes. The impact of solution pH, feed concentration, pressure, and cross-flow velocity on boron rejection and permeate flux was determined. The membranes used were the Toray TM UTC-80-AB and Filmtec TM SW30HR. A lab-scale cross-flow flat-sheet configuration test unit was used for all RO experiments. Seawater sample was collected from the Mediterranean Sea, Alanya-Kızılot shores, south Turkey. For all experi-ments, mass balances were between 91% and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Operation modes did not have any impact on boron rejection, indicating that boron rejection were independent of feedwater boron concentrations up to 6.6 mg/L. For both membranes, much higher boron rejection were obtained at pH of 10.5 (>98%) than those at original seawater pH of 8.2 (about 85–90%). Permeate boron concentrations less than 0.1 mg/L were easily achieved at pH 10.5 by both membranes. The dissociated boron species are dominant at this pH, thus both electrostatic repulsion and size exclusion mechanisms are responsible for the higher boron rejection. The rejection of salts in seawater did not correlate with boron rejection at constant conditions. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5, which may be partially explained by membrane fouling and enhanced scale formation by Mg and Ca compounds from concentration polarization effect at higher pH values. While somewhat higher boron rejection was found for one membrane type as the pressure was increased from 600 to 800 psi, increasing pressure did not affect boron rejection for the other membrane. Feed flowrate thus the cross-flow velocity (0.5–1.0 m/s) did not exert any significant impact on boron rejection at constant conditions.
The formation of deposit on the membrane surface (fouling) is one of the major operating problems of membrane distillation process. The influence of fouling on the performance of this process was investigated during the concentration of wastewater with proteins, bilge water, brines, and the production of demineralized water. The experiments were performed with polypropylene capillary membranes. The morphology and composition of the fouling layer were studied using Fourier transform infrared with diffuse reflectance spectroscopy and scanning electron microscopy coupled with the energy dispersing spectrometry. Fouling with various intensity was observed in most of the studied cases. Permeate flux decline was mainly caused by an increase in the heat resistance of the fouling layer. However in the case of non-porous deposit, a magnitude of the permeate flux was also determined by a resistance of water transport through the deposit layer. It was found the deposits were formed not only on the membrane surface, but also inside the pores. Salt crystallization in the membrane pores besides their wetting, also caused the mechanical damage of the membrane structure. The intensity of the fouling can be limited by the pretreatment of feed and a selection of the operating conditions of membrane distillation.
Membrane distillation (MD) is an emerging technology for separations that are traditionally accomplished by conventional separation processes such as distillation or reverse osmosis. Since its appearance in the late of the 1960s and its development in the early of 1980s with the growth of membrane engineering, MD claims to be a cost effective separation process that can utilize low-grade waste and/or alternative energy sources such as solar and geothermal energy. As an attractive separation process, MD has been the subject of worldwide academic studies by many experimentalist and theoreticians. Unfortunately from the commercial stand point, MD has gained only little acceptance and yet to be implemented in industry. The major barriers include MD membrane and module design, membrane pore wetting, low permeate flow rate and flux decay as well as uncertain energetic and economic costs. This study is an attempt to establish a framework for better understanding the MD process and to consider all possible solutions developed so far to overcome its barriers. Unlike the usual trend pursued in review papers, MD studies have been cited in the present manuscript and classified in tables according to their most important contribution in MD development. These tables cover most important aspects of the MD process and are presented in a simple manner for a glance understanding the effects of different factors and operating variables on the productivity of each MD configuration. Among the different MD papers, those involving theoretical models are pointed out. The areas within the MD field that are either usually or rarely studied are highlighted. Some useful technical discussions based on acquired knowledge from experience and information gathered from MD literature are included. In some way, this paper will help new researchers in the field of MD to quickly be updated avoiding repetition of already known studies. In fact, although the effects of some operating parameters are generally agreed upon, still new researches appear with almost the same results.
In this paper, a pilot vacuum membrane distillation device, using polypropylene hollow fiber, was designed and installed on a seagoing vessel to investigate the operating conditions. During operation, the incoming seawater was heated by the waste-heat generated from the vessel engine. It was found that this device could reach a desalting degree of 99.99% and a membrane flux of 5.4 kg/m2h at 55°C and −0.093 Mpa. The results obtained from this pilot test are in accord with the previous lab experiment results.
Membrane distillation (MD) is one of the non-isothermal membrane separation processes used in various applications such desalination, environmental/waste cleanup, food, etc. It is known since 1963 and is still being developed at laboratory stage for different purposes and not fully implemented in industry. An abrupt increase in the number of papers on MD membrane engineering (i.e. design, fabrication and testing in MD) is seen since only 6 years ago. The present paper offers a comprehensive MD state-of-the-art review covering a wide range of commercial membranes, MD membrane engineering, their MD performance, transport mechanisms, experimental and theoretical modeling of different MD configurations as well as recent developments in MD. Improved MD membranes with specific morphology, micro- and nano-structures are highly demanded. Membranes with different pore sizes, porosities, thicknesses and materials as well as novel structures are required in order to carry out systematic MD studies for better understanding mass transport in different MD configurations, thereby improving the MD performance and looking for MD industrialization.
Greenhouse gas emissions from international transport contribute to anthropogenic global warming, yet these emissions are not liable under the Kyoto Protocol. International attention is being given to quantifying such emissions. This paper presents the results of research into international cruise ship journeys to and from New Zealand. CO2 emissions from such journeys were calculated using an activity based, or "bottom-up", model. Emissions factors for individual journeys by cruise ships to or from New Zealand in 2007 ranged between 250 and 2200 g of CO2 per passenger-kilometre (g CO2 per p-km), with a weighted mean of 390 g CO2 per p-km. The weighted mean energy use per passenger night for the "hotel" function of these cruise vessels was estimated as 1600 MJ per visitor night, 12 times larger than the value for a land-based hotel. Using a simple price elasticities calculation, international cruise journeys for transport purposes were found to have a greater relative decrease in demand than plane journeys when the impact of carbon pricing was analysed. The potential to decrease the CO2 emissions per p-km was examined, and if passenger accommodation was compacted and some luxury amenities dispensed with values similar to those of economy-class air travel were obtained.
Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.
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