Analysis of Regarding the Quality of Potable Water - Report Example

Table of Contents Background: 1 Aim: 2 Objectives: 3 Papers Reviewed: 4 Ethical Considerations: 13 Conclusion: 13 References 14 Table of Figures Figure 1: Global desalination capacities[4] 4 Figure 2: global desalination water sources[4] 5 Figure 3: Different MD configurations[6] 7 Figure 4: Exciting Direct Contact Membrane Distillation model (single acting membrane) 8 Figure 5: Direct Contact Membrane Distillation (double acting membrane) 9 Figure 6: Schematic of a solar pond[5] 12 List of Tables Table 1: Some marketable membranes generally utilized in MD[10]. 11 Background: Potable water constitutes only 2.5% to 3% of the entire water on planet, with only 0.01% being accessible for human use[1], [2]. With [4] the remainder being trapped in glaciers and polar ice caps[2]. In arid areas, where fresh water lake system and low rainfall limit the availability of water necessary for daily life, climatic conditions must also be considered. Furthermore, growth in global population places increasing pressure on the demand for fresh water[2]. Due to these factors, the need to establish sustainable and affordable fresh water sources is crucial. For coastal areas, desalination provides a solution for potable water scarcity [3]. The discussions regarding the quality of portable water remain multifaceted. Technological in the process of producing portable water has shifted attention with direct contact membrane distillation (DCMD) remaining the centre of focus among different studies [FAB02]1. However, these contestations need assessment in terms of different variables including the methodological applicability of its use when it comes to sustainability energy input. Additionally, studies have noted that an understanding of DCMD needs to take consideration of operating parameters like ionic strength on permeate flux, hydrodynamic conditions and transmembrane temperature difference [3]. From these studies, a gap in knowledge exists where a research needs to draw on qualitative and quantitative approach to develop a method of producing potable water through sustainable means. Electrodialysis (ED) and reverse osmosis (RO) remain as the most commercially used membrane technologies adopted in the process of producing water. However, these methods are preferred as they offer among other things, lower specific water production cost and lower specific power consumption [1]. While the two options provide framework in the production of portable water, sustainability has become essential principle in portable water. Furthermore, there is need for a research that develops from drawbacks of these membranes such as environmental pollution because of discharge of concentrated water and fouling phenomena [3]. Aim: This project aims to develop a method of producing potable water through sustainable means. The aim is achieved by investigation of the efficiency of direct contact membrane distillation (DCMD) in sustainable water production, coupled with sustainable energy input using solar pond technology. This investigation is both theoretical and experimental in nature, incorporating physical laboratory experiments and analysis of results. The aim of the research provides the broad point regarding the concept the research hopes to accomplish and the desired outcome from the process of researching. Since the research attempts to explore sustainable energy input using solar pond technology, the aim focuses on long-term outcomes intended to ascertain recent trends in membrane technologies adopted in the process of producing water. In addition, the aim introduces what is missing from the papers reviewed thus identifying the gap in knowledge. The gaps in knowledge (sustainable water production and optimization of the PTFE membrane with the aid of CFD) as proposed and further discussed in the papers reviewed will thus provide the linkage or concordance between the identified aim and parts of central hypotheses that defines the research topic. Objectives: The objectives of the project will be: Understand different water desalination technologies. Investigate sustainable water production. Optimize the PTFE membrane with the aid of CFD Couple DCMD with sustainable energy (solar pond technologies). To prepare a sustainable solution for the discharge brine from the direct contact membrane distillation The research has identified four research objectives in order to provide connectedness between a method of producing potable water and the efficiency of direct contact membrane distillation. The first objective integrates research findings to help in having research plan and data collection on the other hand; the second objective looks at production of portable water in terms of sustainable water production [1]. The objective is specific in its approach as it links qualitative and quantitative data with the research problem. The third and fourth objectives integrate researches to show that the research proposal will be looking for actionable information and knowledge from qualitative research. Generally, the four research objectives challenge theories and assumptions that have been used in understanding membrane technologies adopted in the process of producing water. That is, they test the conformity and validity of the assumptions and theoretical models on membrane technologies and other technologies other than DCMD. To this regard, these objectives help this proposal confirm that the study will pose a sound research question that help in data collection and answering the research aim. For instance, optimisation of the PTE membrane with the help of CFD calls for the objective to understand the scalability, scope, sustainability and size of the research topic ([1]). As such, we use the objectives to define both the dependent variable as the focus of this proposal and independent variable as the causal factor that will influence the problem of the research. Papers Reviewed: Desalination is the removal of sodium chloride NaCl (salt) from seawater to enable it to be used for human activities[3]. The desalination system ordinarily comprises of three primary parts; desalination unit, energy and water source, which these parts are the assessment of the any desalination plant execution. Water source could be either seawater or saline water as shown in figure 2[4]. Figure 1: Global desalination capacities[4] Figure 2: global desalination water sources[4] The desalination procedures could be classified as three unique classes: the primary sort of desalination is thermal separation which incorporates stage changing; this strategy contains variation modes, for example, the multiple effect evaporation (MEE), the single effect evaporation and the multistage flash (MSF)[5]. The other procedure is membrane desalination, which incorporates reverse osmosis (RO); in this procedure new water under high pressure goes through semi-porous membranes. The other kind of membrane desalination is electro-dialysis (ED); in this technique salt particles are transported through particle trade membranes to another arrangement; this is finished by the distinction in electric potential[5]. The third procedure is membrane distillation (MD); the separation is thermally determined as the stage changes. The water vapor experiences through non-wetted pores of the hydrophobic membrane. It is significant that the main impetus of the separation is the vapor weight, which is an aftereffect of the temperature contrast between the two sides of the membrane[5]. However, current desalination procedures such as reverse osmosis (RO) and MSF have the higher energy costs[3]. Whereas, membrane distillation can reduce the energy cost during production through improved efficiency [3]. There is general understanding among studies that the mass transfer in this process takes place by evaporation of what is as a volatile solvent (water) or volatile solute [4]. The factor that drives mass transfer in the process is mass transfer is vapour pressure difference existing across the membrane. Studies recognize that there are three distinct energy inefficiencies in MD [4]. The first case is the polarization of temperature, which happens across the membrane. On the other hand, the second is the resistance to vapour flow through the membrane, which happens because of the presence of trapped air within the pores [3]. The third energetic inefficiency is a conductive heat loss through membrane. Previous research findings that assessed the connectedness between energetic inefficiencies in MD focused their thesis statements on the impacts of either resistance to vapour or polarization in the pores when it comes to performance of pores. However, to have a general understanding of these inefficiencies and link them to the research topic, the three inefficiencies are considered simultaneously in a given system, and as such, the mass transfer of water vapour as it passes the membrane is enhanced. Just like any other processes, desalination has by-products to that need considerations. First, the process requires pretreatment as well as cleaning of chemicals, which are part of the water before desalination. Some of these chemicals include hydrogen peroxide, chlorine and hydrochloric acid. However, once they have lost their ability to clean water they become environmental concern. On the other hand, the process of desalination is associated with brine as the side product. In as much as the purified water keeps human life safe, desalination plants would pump this brine back to other water bodies including oceans thus presenting another level of environmental drawback [3]. The disadvantage of any desalination system is high-energy utilization with associated gas emission and pollution consequences[5]. Additionally, the effect of high volume brackish water discharge on the nature becomes a progressively significant problem and investigators across the planet have announced that disallowed saline poses represent a possibly genuine danger to the marine environments[5]. In addition, there are four sorts of membrane distillation as shown in figure 3[6]. Where direct contact membrane distillation (DCMD) is easy to setup in laboratory and has an adequately high fluidity rate[6]. Of equal importance, is the capability of direct contact membrane distillation (DCMD) to improve the quality of the finished product[6]. Figure 3: Different MD configurations[6] However, the figure 3 provides an understanding on mass transfer in DCMD. Accordingly, mass transfer in DCMD takes place in a three-step process that involves the following: Combined diffusive as well as convective transport of vapours as they pass through the pores of the membrane Diffusive transport from the feed steam to the interface of the membrane A process of condensation of the vapours on the interface of the membrane on the product side of very same membrane Details of the three factors are elaborated in figure 4 below where in the configuration; there is a feed solution at elevated temperature being in contact with one side of the membrane and on the other hand, the colder water being in contact with the opposite side of the membrane. According to the figure below, it is generally the difference in temperature difference existing between the liquids and to some level, their solute concentration that is considered to be inducing the vapour pressure gradient for the transfer of mass. As already discussed, mass transferrin DCMD is a three steps process. Figure 4: Common DCMD Apparatus [3] As it can be seen in figure 4, DCMD has two sides, where the right side is the permeate side and the left side is the feed side, also the membrane will be in contact with these two sides. Figure 4: Exciting Direct Contact Membrane Distillation model (single acting membrane) The designed model will have a double acting membrane, which will have two sides of permeation (top and bottom) and one feed side (middle), as illustrated in the figure 5. Where two membranes will be in contact between the permeate sides and the feed side. Figure 5: Direct Contact Membrane Distillation (double acting membrane) Reasons for choosing MD are the following: ability to operate in higher saline concentration[7] capability to run at lower temperatures[7] ability to operate at lower pressures[7] can operate intermittently (i.e. stop for periods of time and restart anytime without any problem)[7] can be coupled with sustainable energy It merits saying that the procedure of desalination requires a large amount of energy to separate salt from seawater. This procedure is exceptionally costly and not all nations can manage the costs[5]. In addition, ordinary desalination forms have a high focused transfer with salinity of 70,000 PPM[5]. Such dismissal is a genuine risk to the earth[5]. It is likely that the introduced limit of desalinated water will bring about major issues related to energy consumption and the brine produced will impact the environment[5]. Thus, a neighborly arrangement ought to be found to manage the energy consumption and the brackish water. For example, use of sustainable energy to diminish carbon impression and the cost. Similarly, a zero fluid Discharge (ZLD) technique that reuses and treats the saline solution, could be a superior alternative for controlling the water delivered, as it is economical and does not harm the earth[5]. Methodology: Literature review to gain background and technical knowledge, and to ascertain the most suitable membrane material to achieve the desired results during desalination. Again, the literature further will not only provide answers within the context of the efficiency of DCMD in sustainable water production but also provide context and background to the theoretical frameworks and problems faced different water desalination technologies as enumerated in the research background information above. CFD simulation to optimize the design and operating parameters will be performed using commercial CFD code Ansys CFX. However, we introduce the design and operating parameters to deviate ways in which studies continue to view CFD simulation. Specifically, CFD simulation ascertains the extent to which DCMD can be one of the effective MD process in which it deviates from other researches and in such case, how the hydrophobic membrane can be in direct contact only with liquid phases, feed water from the one hand and distilled water on the other. Laboratory experiments to test the efficiency of the DCMD in terms of sustainable heat/mass transfer and to assess the quality of fresh water output: Where formulas of heat and mass transfer will be defined by using Matlab to obtain results post-experiments stage. In terms of mass and heat exchange, the experimental results will be compared with the simulation resulted obtained using Ansys(CFD). Comparison and analysis of results with previous research to assess the success of the investigation: Comparison of results with results from previous studies. For example, one type of membrane will be simulated by Ansys (CFD), and the results that will be conducted from Ansys will be compared with previous studies, in terms of heat flux and mass flux through the membrane. Due to time and cost constraints, this study will focus on one type of membrane only. A PTFE membrane has been specifically selected for this investigation for its high salt rejection and hydrophobic properties[8]: The membrane material impact is still under examination. Actually, marketable hydrophobic microporous membranes created of polymers such as polyethylene (PE), Polytetrafluoroethylene (PTFE), Polyvinylidene fluoride (PVDF) and Polypropylene (PP) have been utilized as a part of MD examinations. These membranes are accessible in tube, flat sheet or cylindrical forms. The geomorphology organization of these membranes nearly accomplishes all the desires of membranes for MD systems. Though, these membranes were initially created for nanofiltration (NF) and microfiltration (MF) justification and the information (membrane descriptions) provided by the makers are attributes for NF and MF. The announced descriptions by the makers are not yet adequate for the selection of the membrane for DCMD system[9]. Dimensions of the water driven porousness are not pertinent for membranes to be involved in MD procedure, because the water pervasion contains fluid mass exchange mechanisms other than vapour transport. Table 1: Some marketable membranes generally utilized in MD[10]. Membrane trade name Manufacturer Material Thickness () Average pore size (m) Porosity (%) TF200 Gelman PTFE/PPa 178 0.20 80 TF450 0.45 TF1000 1.00 GVHP Millipore PVDFb 110 0.22 75 HVHP 140 0.45 S6/2 MD020CP2N AkzoNobel Microdyn PPc 450 0.2 70 a Flat-sheet Polytetrafluoroethylene membrane supported by polypropylene net. b Flat-sheet Polyvinylidene fluoride membranes. c Polypropylene capillary membrane: number of capillaries in membrane module: 40; effective filtration area 0.1m2; inner capillary diameter: 1.8 mm; length of capillaries: 470 mm. Table (1) review separately the capillaries, hollow fibre and flat sheet marketable membranes generally utilized as a part of MD studies together with their main features as stated by the makers. Detailed clarifications of the utilized features procedures of some marketable membranes might be discovered somewhere else. Likewise, the membrane areadoes not significantly affect the mass flux rate, but it decreases the particular energy consumption substantially[10]. Solar energy will be utilized, where applicable, during the distillation process in these experiments to improve sustainability: Salinity gradient solar ponds are substantial pool of salt water that has the capability of sorting and gathering heat energy[5], in salinity gradient solar pond, the centralization of the disintegrated salt in the water increases with depth from top to bottom. The salinity gradient solar pond has three regions as shown in figure 6, the Upper Convective Zone (UCZ), the density in this district is unchanging and approximately equivalent to the fresh water density. The gradient zone (NCZ), the density in this district increases linearly with the depth. The lower zone or (LCZ), it is described of having unchanging high density and temperature[5]. Figure 6: Schematic of a solar pond[5] Possibly there will be collaboration with RMIT University in Australia. Ethical Considerations: Ethical consideration in DCMD desalination research follows guidelines provided by the National Society of Professional Engineers Code of Ethics. Accordingly, the code of ethics will be significant in my decision-making processes, as it will entail all the responsibility as engineer. One of the ethical provision of the Codes of Ethics is that a research should hold paramount the safety, health and welfare of the public. From this point, it will be in the best interest of the public that this study will assess approaches handling and disposing research materials before and after the research. This decision will be influenced by the fact that the Code of Ethics expects that researches should at all times, strive to serve interest of the public. The Code of Ethics provides this research with guidelines of influencing my decisions to research on materials and methods that seek to help better quality of portable water for all people. Conclusion: Direct contact membrane distillation (DCMD) system will be investigated computationally and experimentally in order to optimize heat and mass transfer. This will provide a ground for understanding a new approach for the operation and design of DCMD for desalination. On the other hand, the research process seeks to demonstrate the extent to which careful configuration of the MD system as well as design of a membrane module could simultaneously aspects such as permeability obstruction of the DCMD and temperature polarization. We recognize that as far as economic benefit of DCMD is concerned, it is difficult to estimate what would be a full-scale performance especially when basing on bench scale results. However, the study develops from different pilot scale tests having a large membrane module operated in advanced DCMD mode to provide even a more accurate data needed for economic analysis. In developing the research, we will be concerned with. References [1] S. L. Postel, G. C. Daily and P. R. Ehrlich, "Human appropriation of renewable fresh water," Science, vol 271, no 5250, pp. 785-788, 1996. [2] D. Hinrichsen and H. Tacio, "The coming freshwater crisis is already here," The linkages between population and water.washington, DC: Woodrow wilson international center for scholars, pp. 1-26, 2002. [3] K. Nakoa, K. Rahaoui, A. Date and A. Akbarzadeh, "An experimental review on coupling of solar pond with membrane distillation," Solar energy, vol 119, pp. 319-331, 9 2015. [4] S. Lattemann, M. D. Kennedy, J. C. Schippers and G. Amy, "Chapter 2 global desalination situation," Sustainability science and engineering, vol 2, pp. 7-39, 2010. [5] K. Nakoa, K. Rahaoui, A. Date and A. Akbarzadeh, "Sustainable zero liquid discharge desalination (SZLDD)," Solar energy, vol 135, pp. 337-347, 10 2016. [6] Z. Lei, B. Chen and Z. Ding, "Special Distillation Processes," in Chapter 6 - membrane distillation, Z. Lei, , B. Chen, , and Z. Ding, Eds. Amsterdam: Elsevier Science, 2005, pp. 241- 241-319. [7] L. Camacho, Lucy Mar Camacho, Ludovic Dumee, Jianhua Zhang and Jun-de Li, "Advances in membrane distillation for water desalination and purification applications," Water (basel), vol 5, no 1, pp. 94; 94-196; 196, .03.2013 01. [8] J. Zhang, J. Li and S. Gray, "Effect of applied pressure on performance of PTFE membrane in DCMD," Journal of membrane science, vol 369, no 1–2, pp. 514-525, 3/1 2011. [9] M. M. A. Shirazi, A. Kargari and M. Tabatabaei, "Evaluation of commercial PTFE membranes in desalination by direct contact membrane distillation," Chemical engineering and processing: Process intensification, vol 76, pp. 16-25, 2 2014. [10] M. Khayet, J. I. Mengual and T. Matsuura, "Porous hydrophobic/hydrophilic composite membranes: Application in desalination using direct contact membrane distillation," Journal of membrane science, vol 252, no 1–2, pp. 101-113, 4/15 2005.   Read More

Aim: This project aims to develop a method of producing potable water through sustainable means. The aim is achieved by investigation of the efficiency of direct contact membrane distillation (DCMD) in sustainable water production, coupled with sustainable energy input using solar pond technology. This investigation is both theoretical and experimental in nature, incorporating physical laboratory experiments and analysis of results. The aim of the research provides the broad point regarding the concept the research hopes to accomplish and the desired outcome from the process of researching.

Since the research attempts to explore sustainable energy input using solar pond technology, the aim focuses on long-term outcomes intended to ascertain recent trends in membrane technologies adopted in the process of producing water. In addition, the aim introduces what is missing from the papers reviewed thus identifying the gap in knowledge. The gaps in knowledge (sustainable water production and optimization of the PTFE membrane with the aid of CFD) as proposed and further discussed in the papers reviewed will thus provide the linkage or concordance between the identified aim and parts of central hypotheses that defines the research topic.

Objectives: The objectives of the project will be: Understand different water desalination technologies. Investigate sustainable water production. Optimize the PTFE membrane with the aid of CFD Couple DCMD with sustainable energy (solar pond technologies). To prepare a sustainable solution for the discharge brine from the direct contact membrane distillation The research has identified four research objectives in order to provide connectedness between a method of producing potable water and the efficiency of direct contact membrane distillation.

The first objective integrates research findings to help in having research plan and data collection on the other hand; the second objective looks at production of portable water in terms of sustainable water production [1]. The objective is specific in its approach as it links qualitative and quantitative data with the research problem. The third and fourth objectives integrate researches to show that the research proposal will be looking for actionable information and knowledge from qualitative research.

Generally, the four research objectives challenge theories and assumptions that have been used in understanding membrane technologies adopted in the process of producing water. That is, they test the conformity and validity of the assumptions and theoretical models on membrane technologies and other technologies other than DCMD. To this regard, these objectives help this proposal confirm that the study will pose a sound research question that help in data collection and answering the research aim.

For instance, optimisation of the PTE membrane with the help of CFD calls for the objective to understand the scalability, scope, sustainability and size of the research topic ([1]). As such, we use the objectives to define both the dependent variable as the focus of this proposal and independent variable as the causal factor that will influence the problem of the research. Papers Reviewed: Desalination is the removal of sodium chloride NaCl (salt) from seawater to enable it to be used for human activities[3].

The desalination system ordinarily comprises of three primary parts; desalination unit, energy and water source, which these parts are the assessment of the any desalination plant execution. Water source could be either seawater or saline water as shown in figure 2[4]. Figure 1: Global desalination capacities[4] Figure 2: global desalination water sources[4] The desalination procedures could be classified as three unique classes: the primary sort of desalination is thermal separation which incorporates stage changing; this strategy contains variation modes, for example, the multiple effect evaporation (MEE), the single effect evaporation and the multistage flash (MSF)[5].

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