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  • Renewable and Sustainable Energy Reviews 14 (2010) 26412654

    Renewable and sustainable approaches for desalination

    Veera Gnaneswar Gude a, Nagamany Nirmalakhandan b, Shuguang Deng a,*a Chemical Engineering Department, New Mexico State University, Las Cruces, NM 88003, USAb Civil Engineering Department, New Mexico State University, Las Cruces, NM 88003, USA

    Contents

    1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2642

    2. Desalination technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2642

    3. Energy and greenhouse gas emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2642

    4. Water and energy sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2643

    4.1. Utilizing renewable energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2643

    4.1.1. Use of solar energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2644

    4.1.2. Solar collectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2644

    4.1.3. Solar pond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2644

    4.1.4. Photovoltaic modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2645

    4.1.5. PV thermal collectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2645

    4.1.6. Use of geothermal energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2645

    4.1.7. Use of wind energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2646

    4.1.8. Use of wave energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2646

    4.2. Process hybridization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2647

    4.2.1. Coupling MSF with RO process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2647

    4.2.2. Integrating membrane distillation (MD) with other desalination processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2647

    4.2.3. Hybrid membrane process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2648

    4.3. Low-cost and low-energy desalination technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2648

    4.3.1. Utilization of low-grade waste heat sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2648

    4.3.2. Low-temperature desalination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2649

    4.4. Water reuse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2649

    A R T I C L E I N F O

    Article history:

    Received 5 August 2009

    Accepted 14 June 2010

    Keywords:

    Desalination

    Renewable energy

    Energy cost

    Water reuse

    Reverse osmosis

    Cogeneration

    Green house gases

    Environment

    A B S T R A C T

    Freshwater and energy are essential commodities for well being of mankind. Due to increasing

    population growth on the one hand, and rapid industrialization on the other, todays world is facing

    unprecedented challenge of meeting the current needs for these two commodities as well as ensuring

    the needs of future generations. One approach to this global crisis of water and energy supply is to utilize

    renewable energy sources to produce freshwater from impaired water sources by desalination.

    Sustainable practices and innovative desalination technologies for water reuse and energy recovery

    (staging, waste heat utilization, hybridization) have the potential to reduce the stress on the existing

    water and energy sources with a minimal impact to the environment. This paper discusses existing and

    emerging desalination technologies and possible combinations of renewable energy sources to drive

    them and associated desalination costs. It is suggested that a holistic approach of coupling renewable

    energy sources with technologies for recovery, reuse, and recycle of both energy and water can be a

    sustainable and environment friendly approach to meet the worlds energy and water needs. High capital

    costs for renewable energy sources for small-scale applications suggest that a hybrid energy source

    comprising both grid-powered energy and renewable energy will reduce the desalination costs

    considering present economics of energy.

    2010 Elsevier Ltd. All rights reserved.

    Contents lists available at ScienceDirect

    Renewable and Sustainable Energy Reviews

    journa l homepage: www.e lsev ier .com/ locate / rser

    * Corresponding author. Tel.: +1 575 646 4346; fax: +1 575 646 7706.

    E-mail address: sdeng@nmsu.edu (S. Deng).

    1364-0321/$ see front matter 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.rser.2010.06.008

    http://dx.doi.org/10.1016/j.rser.2010.06.008mailto:sdeng@nmsu.eduhttp://www.sciencedirect.com/science/journal/13640321http://dx.doi.org/10.1016/j.rser.2010.06.008

  • V.G. Gude et al. / Renewable and Sustainable Energy Reviews 14 (2010) 264126542642

    5. Selection criteria for a desalination process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2649

    6. Desalination cost estimations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2650

    7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2652

    References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2652

    1. Introduction

    Freshwater and energy are two inseparable and essentialcommodities for sustaining human life on earth. Rapid populationgrowth and industrialization, especially in developing countries inthe recent past, have placed pressing demands for both freshwaterand energy. Supply of freshwater requires energy and unfortu-nately, many countries in the world that lack freshwater sources,are also deficient in energy sources. While conventional watertreatment technologies are adequate to treat surface and groundwaters with low dissolved solids [

  • Table 2Principal characteristics of different desalination processes.

    Characteristic Type of process

    Phase change Non-phase change Hybrid

    Nature Thermal process: MED, MSF, MVC, TVC

    (evaporation and condensation)

    Pressure/concentration gradient

    driven: RO (membrane separation,

    ED (electrochemical separation)

    Thermal + membrane: membrane

    distillation, MSF/RO, MED/RO

    Membrane pore size 0.13.5 nm 0.20.6 mmFeed temperature 60120 8C

  • [(Fig._1)TD$FIG]

    Fig. 1. Possible combinations of renewable energy sources with desalination processes.

    Table 6Possible combinations of solar collectors with desalination technologies.

    Type of solar collector Source of

    salt water

    Desalination

    process

    Direct solar Seawater,

    brackish water

    Solar stills

    Flat panel collectors Seawater MED/LTMED

    Evacuated tube collectors Seawater MSF/TVC

    Parabolic trough collectors Seawater MED/MEB

    Photovoltaic thermal collectors Seawater,

    brackish water

    MED/LTMED

    V.G. Gude et al. / Renewable and Sustainable Energy Reviews 14 (2010) 264126542644

    4.1.1. Use of solar energy

    4.1.1.1. Solar distillation. Direct utilization of solar energy fordesalination is by solar stills. Solar energy can be used directly toevaporate water from the sea/brackish and other impaired watersfor household or community water supplies. Construction of solarstill is simple and is most suitable for areas where the hardwaresources are limited. Solar distillation exhibits considerableeconomic advantage over other present technologies because ofits use of free energy and very low operating costs. Distillation withsolar energy is a most favorable process for small compact waterdesalting at geographical locations where there is considerablesolar radiation. Another advantage is its simplicity (no movingparts) as it requires low operation and maintenance skills and ishighly reliable. Solar stills have been proven to be successful inremoval of bacteria, volatile and non-volatile contaminants ifproper care were taken to eliminate the contamination of distillatewith the feed water [18]. Solar stills can provide necessary dailyamount of drinking water for water scarce and drought areas likeAfrica, Asian countries, etc. [19]. The first large-scale solar-powered desalination plant was installed in Las Salinas, Chile in1874 with solar still area of 4700 m2 which was operated for about40 years [20,21]. However, design problems encountered withsolar stills are brine depth, vapor tightness of the enclosure,distillate leakage, methods of thermal insulation, and cover slope,shape and material [22]. Typical still efficiency of 35% with a lowproductivity of 34 L/m2 and large area requirements are twoother factors that prevent large-scale applications of solar stills.

    4.1.2. Solar collectors

    Solar energy is abundant on the earth and the worldwideconsumption of energy is only a 1/16,000 of incoming solar energy[23]. Solar collectors can harvest the solar energy in thermal formwhich, in turn, can be utilized to drive MSF, MED and MDprocesses. Table 6 presents the possible combinations of solarcollectors with available desalination technologies.

    4.1.3. Solar pond

    Utilizing solar ponds to drive desalination processes has beendemonstrated in many parts of the world. Among many studies,one that is of noteworthy is the work performed by the Universityof Texas at El Paso (UTEP) on thermal desalination powered by

    salinity-solar ponds through the support of the U.S. Bureau ofReclamation. Two falling-film, multi-stage flash (MSF) distillationunits (Spinflash) have been tested intermittently during theperiods of 19871988 and 19901992, respectively [24]. Thepond has a surface area of 3000 m2 (0.75 acre) and a depth of about3.25 m (10.7 feet). A multi-effect multi-stage (MEMS) desalinationunit was coupled with a solar pond and the performance of thedesalination system was measured using different feed water TDSranging from 1650 to 58,000 ppm. The process operated in thetemperature range of 6380 8C with fresh water production ratesbetween 2.3 and 7.2 m3/day and the specific energy consumptionfor the four stage unit varied between 735 and 1455 kJ/kgdepending on the process configuration, feed water TDS andcooling stream temperature.

    Walton and Lu [25,26] have reported on a salinity gradient solarpond that takes the advantage of the temperature gradient to drivethe membrane distillation process. In this system, hot brine waspumped from the bottom of the solar pond and passed through aheat exchanger to supply heat. Cold water from the surface of thesolar pond was passed through a heat exchanger to providecooling. High and low temperatures for system operation wereobtained by changing the flow rates for solar pond hot and coldwater. Flux per unit area of membrane surface ranges from 0 to 6 L/m2/h. Flux was measured down to hot side temperatures as low as13 8C. Flux per unit temperature drop at very low temperatureswas only reduced about 50% compared to flux at highertemperatures. This study concluded that operation of MD at suchlow temperatures may open up thermal energy resources that havenot previously been considered for desalination.

  • V.G. Gude et al. / Renewable and Sustainable Energy Reviews 14 (2010) 26412654 2645

    In another study, a power plant combined with MSF/MEDdesalination plants used a solar pond. As the power plant operatedfor only 4 h a day, the exhaust gases released at 550 8C were usedpartially to drive the desalination process while the rest is used toheat the solar pond. The solar pond stores the rest of the heat andrestores it to the desalination plant the rest of the day. Solar pondsupplies the seawater feed temperature in the range of 95120 8Cat the first stage. The use of 120 MWe gas turbine coupled to theMED technology permits to reach attractive costs around 0.5 US$/m3 [27]. Other solar pond driven desalination plants are a MEDprocess of capacity 3000 m3/day near Dead Sea, MSF process ofcapacity 60 m3/day at Margarita de Savoya, Italia and ME-TVCprocess of capacity 30 m3/day at University of Ancona, Italy[11,28].

    4.1.4. Photovoltaic modules

    A PV-electricity system includes PV arrays, DC inverter andbattery bank. Today, the maximum efficiency of the PV modules isreported as 14.5%. The advantage of employing a battery bank inthe PVRO system is to provide constant energy flow during nighttime and to buffer the variations in the electricity production dueto passing clouds and rainy days.

    The potential combination of solar photovoltaic (PV) powerwith reverse osmosis has generated growing interest because ofinherent simplicity and elegance of both technologies. Thecompatibility of reverse osmosis with solar photovoltaic powerand other renewable energy forms has been greatly enhanced bythe advent of efficient and reliable energy recovery pumps, whichrecycle the hydraulic energy of the reject brine to assist pumpingthe feed wat...

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