Sunday, 05 May 2019 09:55

Glossary

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adiabatic, adiabatic change
An adiabatic change is a thermodynamic process, in which a system changes its condition without exchanging heat and/or mass with its environment.

 

 

 

Anion Exchange Membrane AEM

 

 



anolyte

 

 



anti-corrosives
Chemical agent to reduce the feed water's corrosion potential.

 

 



anti-foaming
Chemical agent to reduce the formation of foam or to break a foam already formed.

 

 



anti-scalant
Chemical agent to reduce scaling disposition of the feed water.

 

 



auxiliary power
Power for auxiliary systems in a desalination plant, for instance electric power supply for control units, circulation pumps, vacuum pumps etc.

 

 



batch mode
Recycling of the brine in several cycles in order to achieve higher brine concentrations.

 

 



bio-electric potential

 

 



brine
Concentrated feed water.

 

 



Capacitive Deionisation, Membrane Capacitive Deionisation Electrochemical Demineralisation, Electrosorption CDI, MCDI

 

 



capacitive ion storage

 

 



Cation Exchange Membrane CEM

 

 



catholyte

 

 



chemical potential μ
The chemical potential is an intensive thermodynamic state variable describing the change in free enthalpy in thermodynamic systems with variable number of atoms or molecules of the species. Desalination-related parameters like osmotic pressure or vapour pressure are derived from the concept of the chemical potential.

 

 

 

Cleaning-in-Place CIP

 

 



concentration ρi, wi, ci, xi
Concentration of a component i (solute) in a solution can be given

• as mass concentration ρi per volume in [kg/m3],
• as mass fraction wi per mass in [-] or in [g/kg],
• as molar concentration ci per volume in [kmol/m3] or
• as molar fraction xi per mol [-] of the solution [xxx_klein].

For standard seawater, the mass fraction of the sum of all solutes is
wSi = 35.00 g/kg [xxx_millero].

For “salt concentration” in seawater, see “salinity”.

 

 

Concentration Factor CF
is the relation between the salinity of the feed water and the salinity of the discarded brine< (“brine out”). In other words, CF is the ratio between feed mass flow to mass flow of the discarded brine and therefore directly connected to the Recovery Ratio RR:

 

 

 

contact angle Θ
The contact angle Θ is the angle, where a liquid–gas interface meets a solid surface. Θ is conventionally measured through the liquid. It quantifies the wettability (see hydrophilic and hydrophobic) of a solid surface by a liquid. The cosine of Θ is a function of the interfacial energies of solid-gas and liquid-solid as well as of the surface tension (interfacial energy of liquid-gas).

 

 

 

counter current
Heat transfer between two fluids in a heat exchanger flowing in opposite directions to each other.

 

 

 

cross current
Heat transfer between two fluids in a heat exchanger flowing in a direction of about 90° to each other.

 

 

 

crystallisation limit
Maximum concentration of a solute in a solvent before crystal formation of the solute starts to occur.

 

 

 

demister
Porous structure, mostly a steel wire mesh, to hold back droplets of saline water from the condenser units in thermally driven desalination systems.

 

 

 

dew point
The dew point is the temperature in humid air, where at a given absolute humidity, water vapour in air reaches saturation or, in other terms, starts to condense.

 

 

 

diffusion
Diffusion (lat. diffundere “pour out”, “scatter”, “spread”) is a natural physical process originating from the Brownian Movement of molecules. After a certain time, it leads to a total mixing of two or more substances due to a homogeneous distribution of the involved particles [xxxRömpp]. Diffusion occurs due to an omnidirectional, statistic movement of particles as a result of their thermal energy and a local difference in concentration, which in the end is a difference in chemical potential.

 

 

 

distillation
In distillation, single components of a liquid mixture are separated by selective vaporisation and condensation. The distillation technique makes use of different partial vapour pressures or in other terms, boiling points (temperatures) of the single components in the mixture.


 

 

electricigen

 

 



Electrodeionisation, Continuous Electrodeionisation EDI, CEDI

 

 



Electrodialysis, Electrodialysis Reversal ED, EDR

 

 



electrical double layer EDL

 

 



Electrosorption

 

 



enthalpy
Enthalpy is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. [xxxoxf1] In other words, enthalpy is the sum of the energy required to create the system and the work to be done to displace its environment and establish its volume and pressure. In desalination applications, mostly the specific enthalpy h in [J/kg] is used, which is the absolute enthalpy H [J] per unit mass [kg].

 

 

 

entropy
Entropy is a thermodynamic property of matter. Based on a comparison of entropy, the viability of thermodynamic transformations can be analysed. Furthermore, irreversibilities or in other words internal losses can be quantified [xxxsat]. In most cases, the generation of entropy stands for thermal or performance losses.

 

 

 

evaporation
Evaporation is a phase change from liquid to vapour (gas) at temperatures lower than the boiling temperature at a given pressure. Evaporation occurs always at the phase boundary to the liquid phase, e.g. the water surface and air in a system. The driving force of evaporative processes is a difference between the vapour pressure of a liquid substance (e.g. water) at the phase boundary and, in case of air, the partial vapour pressure of the gaseous substance (e.g. water vapour) in the air.

 

 

 

exoelectrogen

 



exoelectrogenic

 

 



feed water
Feed water is the raw water to be (pre)treated and fed into a desalination system.


 

 

fouling
Fouling is the deposit of unwanted material on solid, functional surfaces, e.g. heat exchanger surfaces or membranes. Fouling can both be of organic (biofouling) or inorganic (scaling) nature. Both forms mostly reduce the efficiency of the affected surfaces, for instance heat exchanger efficiency due to lower heat transfer coefficients or permeability of a membrane due to a higher flow resistance.


 

 

Gained Output Ratio GOR
The Gained Output Ratio (GOR) is a key figure for the performance of thermally driven desalination systems with superheated steam as main energy source, for instance Multistage Flash (MSF) or Multi-Effect Distillation (MED). GOR denotes the mass flow ratio of produced distillate to consumed heating steam


GOR can be interpreted as quality grade for heat recovery: how often is the heat of evaporation contained in the heating steam reused for vaporizing and condensing (= amount of distillate) pure water. Therefore, GOR values in MSF and MED plants correlate with the number of stages or effects.


 

 

heat capacity rate
The heat capacity rate is the product of the mass flow rate of a liquid and its heat capacity at constant pressure. It is a figure for the amount of enthalpy (total heat content) that can be absorbed or released by a fluid per unit temperature change and per unit time. Heat capacity rates are given in [kJ K-1 s-1] and are an important quantity in heat exchanger theory.

 

 

heat of condensation, enthalpy of condensation ΔhC
Under equal thermodynamic conditions, the heat of condensation is equal to the heat of evaporation with the opposite sign. By definition, in enthalpy changes of evaporation heat is absorbed by the substance (positive sign). On the other hand, in enthalpy changes of condensation, heat is released by the substance (negative sign).

 

 

heat of evaporation, enthalpy of evaporation ΔhV
In order to achieve a phase change of a substance from liquid to gas, a certain amount of energy must be added per quantity of the substance. This amount of energy is the heat or enthalpy of evaporation. The heat of evaporation is a function of the pressure and the temperature at which the phase change takes place.

 

 

heat exchanger
A heat exchanger is a device for exchanging heat between two or more fluids that are at different temperatures [xxxInci]. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact [xxxKak]. For a deeper understanding of heat exchanger technology, please refer to Annex E1.


 

 

Humidification-Dehumidification, Multi-Effect Humidification HD, HDH, MEH
Humidification-Dehumidification (HD, sometimes also HDH or in case of multiple effects “Multi- Effect Humidification” MEH) uses the principle of evaporation of pure water in a humidifier and subsequent condensation of the water vapour in a dehumidifier. A large majority of HD set-ups uses air as a carrier medium. Thus, HD imitates the natural rain cycle in an artificial environment.

The separation of pure water and salt is due to a substantially lower vapour pressure of salt compared to water. At a given temperature, water will evaporate while salt is remaining dissolved in the liquid brine. The fundamental driver of HD is a net vapour pressure difference between feed water, carrier gas (mostly humid air) and condensate. This vapour pressure difference is induced by temperature differences between feed water and condensate, which are commonly generated by heating the feed water (addition of heat).

HD is a thermal low-temperature (60 °C – 85 °C) process and can therefore be driven with solar energy or waste heat. Another key advantage is its robustness towards the feed water quality and its suitability for Zero Liquid Discharge (ZLD) applications.


 

 

hydraulic fracturing, fracking
Hydraulic fracturing or fracking can therefore be classified as a well stimulation technique for the exploitation of crude oil, natural gas or geothermal water deposits, where the required fluids are not automatically flowing towards the wellbore. A so-called “fracking fluid” is injected into the wellbore at high pressure in order to break up the deep-rock formations around the deposit. Through the so-created cracks, the required fluids will flow much easier. When the fracking fluid is removed, it often gained a high salinity and very often contains substances that are harmful for the environment. In this case, desalination techniques may be applied to reduce the amount of waste water and hence costs.

 

 

Hydraulic Retention Time HRT


 



hydrophilic
In desalination applications, the term “hydrophilic molecular entity” mostly stands for the properties of a hydrophilic surface, for instance a Reverse Osmosis (RO) membrane. Hydrophilic substances attract water molecules and have a high solubility in water. Water getting in contact with hydrophilic surfaces will exhibit a low contact angle. The opposite of hydrophilic is hydrophobic. [xxx_chemie, xxx_Arieh]

 

 

hydrophobic
Hydrophobicity is the physical property of a molecule that is repelled from water. In desalination, these are mostly molecules of a membrane, for instance a Membrane Distillation (MD) membrane. Hydrophobicity is commonly seen as an absence of attractive forces between water molecules and the membrane. Hydrophobic molecules mostly are nonpolar, while water molecules are polar. Thus, hydrophobes do not have a high solubility in water. Water getting in contact with hydrophobic surfaces will show a high contact angle. [xxx_chemie, xxx_Arieh]


 

 

latent heat
is the thermal energy released or absorbed by a substance during a process with constant temperature. The application of latent heat usually involves a phase change (solid ↔ liquid, liquid ↔ gaseous or a change in crystal configuration) of the substance and is therefore connected to the terms “heat of evaporation” and “heat of condensation”.


 

 

mass fraction wi
Concentration measure giving the mass of a solute in relation to the mass of the solution in [kg/kg] or consequently dimensionless [–].

 

 

Mechanical Vapour Compression MVC


 



Membrane Distillation MD
Analogous to Humidification-Dehumidification (HD) systems, Membrane Distillation (MD) also uses the principle of evaporation of pure water and subsequent condensation of water vapour in a condenser. The main difference to HD is, that in MD, the evaporation is established across a hydrophobic membrane. This allows for a slightly higher Performance Ratio PR and a much lower need for installation space, whereas HD plants usually have a lower complexity and a higher tolerance to problematic feed waters.

A large majority of MD systems (except Vacuum Membrane Distillation VMD) evaporates water to humid air and therefore is a purely evaporative process. The separation of pure water and salt is due to a substantially lower vapour pressure of salt compared to water. At a given temperature, water will evaporate while salt is remaining dissolved in the liquid brine. Similar to HD, the fundamental driver of MD is a net vapour pressure difference between feed water, humid air and condensate. This vapour pressure difference is induced by temperature differences between feed water and condensate, which are commonly generated by preheating the feed water (addition of heat).

 

 

 

Microbial Desalination Cell MDC

 



molar
A molar unit relates physical or chemical properties of a substance on its amount or its number of particles. The term “number of particles” stands for the number of atoms and/or molecules contained within the respective amount of substance.


 

 

Multi-Stage Flash Evaporation MSF

 



Non-Condensable Gases NCG
A Non-Condensable Gas (NCG) is a gas that cannot be condensed under nominal process conditions [xxxHelle]. In desalination processes, this is typically air or carbon dioxide and other trace gases dissolved in the feed water.

NCG-related problems mostly occur at condenser surfaces of thermally driven desalination processes. In the vicinity of the cold condensate film (or in some cases the dry heat exchanger surface), a negative concentration and temperature boundary layer is developing. A locally reduced water vapour concentration and temperature both lead to a decrease in the (partial) vapour pressure difference between the water vapour in the gas phase and the condensate film. Thus, the driving force for water mass transfer to the condenser is strongly reduced and condensation rates decrease accordingly.
For more details on concentration and temperature boundary layers in desalination applications please refer to Annex D. For NCG-related problems, see Annex D3.


 



packing, packing material
Packing material are small pieces of tube or spheres that mostly are optimized to have a high volume-specific surface and high porosity. The high specific surface is to allow an optimal heat and mass exchange between two liquids, in desalination mostly seawater and air. High porosity is needed for minimum pressure losses for instance of air in Humidification-Dehumidification (HD) humidifiers, thus increasing humidifier performance.


 

 

partial vapour pressure pV,i
The vapour pressure of a single component i in a mixture. According to Dalton’s law, the total pressure of a mixture is always a sum of the partial pressures of its single components [xxxsat]. Therefore, it is obvious, that the partial vapour pressure of a component is not only a function of temperature, but also of concentration of the respective component in the mixture.

The understanding of thermodynamic concepts around (partial) vapour pressure is crucial for the understanding of thermally driven desalination systems. Therefore, a deeper insight into the theory of vapour pressures is provided in
Annex C.


 

 

Performance Ratio PR
The Performance Ratio (PR) as analogue to the Gained Output Ratio (GOR) is a key figure for the performance of thermally driven desalination systems with sensible heat input, like Humidification-Dehumidification (HD) or Membrane Distillation (MD). PR can be directly derived from GOR and denotes the enthalpy ratio of produced condensate to consumed heat
flow Qin:



Note, that for the sake of comparability of plants with different evaporation temperatures and pressures, ΔhV is set to a standard value of 1,000 BTU/lb, which corresponds to 2,326 kJ/kg in SI units.

 

 

permeate
In membrane desalination processes, permeate is the sum of substances, mostly pure water and a small amount of salt, that is percolating through a membrane. Note, that the nature of “percolating” in this context depends on the desalination process. In Membrane Distillation (MD), this can mean evaporation through the membrane, in Reverse Osmosis (RO), it can mean diffusion through the active layer of a membrane.

 

 

 

pretreatment
is the treatment of raw or feed water with the goal to protect the desalination plant and to guarantee given standards for the product water (distillate or permeate).

 

 

 

Rapid Spray Evaporation RSE

 

 



Recovery, Recovery Ratio, Recovery Rate RR
mostly given as Recovery Ratio RR is the relation between the output of desalinated product water to the input of feed water. RR can be expressed as ratio of mass flows


and is generally 0 < RR < 1.

 

 



Reverse Osmosis RO
The main driver of the Reverse Osmosis (RO) process is the application of a pressure difference between feed water and permeate (in desalination: product) across a semi-permeable membrane. This applied pressure difference has a significant influence on the difference in chemical potential between feed and permeate side, which is the universal driving force in RO. Due to this chemical potential difference, pure water flows through a membrane from the feed to the permeate side, while salt is held back at the feed side. The pressure and hence chemical potential difference is applied by a series of electrically driven high-pressure pumps on the feed side.

Due to its versatility and low Specific Energy Consumption (SEC), RO is the most commonly applied technology in the global desalination market [xxxIDA].


 

 

salinity, Knudsen Salinity, Practical Salinity Scale, Practical Salinity Unit w, SK, PSS-78, PSU
By standard definition, the term “salinity” stands for the mass fraction wsalt [gsalt/kgwater] of dissolved salt in a body of pure water. Salinity is a thermodynamic state variable that governs physical properties like density, heat capacity and partial vapour pressure or chemical potential of the components.

Quite often, seawater salinity is described by the Knudsen Salinity SK [ppt], which gives the total amount of all dissolved inorganic material. SK can be determined by boiling off the water component. A more recent unit for seawater salinity is the Practical Salinity Scale PSS-78, which is tailored for salinity measurements using the electrical conductivity. PSS-78 can be given in [g/kg], [ppt], but mostly dimensionless [-]. Sometimes, PSS-78 is given as “Practical Salinity Unit” PSU [-]. [xxxSharkawy]

For standard seawater,
w = 35.00 g/kg, SK = 35.00 ppt, PSS-78 = PSU = 35.0.

Sometimes, the term “Total Dissolved Solids” (TDS) is also used to describe the salinity of water. However, this is not correct, as TDS also contains organic compounds. For the exact composition of seawater, please refer to Annex B – “Thermodynamic Properties of Seawater”.

 

 

 

scaling
The term “scaling” is a sub-category of “fouling” phenomena and refers to the precipitation or crystallization of sparingly dissolved inorganic compounds of the feed water on a solid host material [xxxKhayet]. The host material mostly is a functional surface like a heat exchanger wall or a membrane.

 

 

 

sensible heat
In the context of heat transfer, sensible heat in- or output appears as a temperature change of a medium, which can be detected (= sensed) by a temperature sensor. In sensible heat transfer, no phase change is involved, see also “latent heat”.

 

 

 

Solar Still
Solar Stills follow the same operation and separation principles as Humidification-Dehumidification (HD) installations. The fundamental driver also is similar. The unique features of Solar Stills are
(1st) the necessity to operate them with Solar (Thermal) Energy;
(2nd) the integration of humidifier and dehumidifier in one casing, which additionally serves as solar thermal heater.

Whereas the main advantage compared to other HD systems is the robustness and simplicity of Solar Stills, this goes at the expense of a good heat recovery or in other terms of high Performance Ratios.



 

 

Specific Energy Consumption SEC
Consumption of the main driving energy per unit of fresh water (condensate or distillate in thermal units, permeate in membrane systems). SEC is given in [kWh/m3] of distillate. Note that the auxiliary energy consumption mostly is not included!

 

 

 

sponge balls
A sponge ball cleaning system is used to clean the tubes in a tube bundle heat exchanger. The core parts are sponge rubber balls that are oversized in relation to the tubes to be cleaned. By circulating (i.e. through pumping) the sponge rubber balls through the tubes, fouling layers are removed. This results in a permanently good heat transfer. [xxxTapro]

 

 

 

standard seawater
As salinity and chemical composition in the oceans is widely varying, a standard composition of seawater for scientific purposes has been defined. Mostly, the standard salt concentration is given with 35.00 g of salt per kg solution or roughly 35,000 ppm. For a deeper understanding of chemical and thermodynamic properties of seawater please refer to Annex B.

 

 

 

stripping
Stripping is a physical separation process, where specific components of a liquid mixture are removed by a carrier gas. The liquid stream and carrier gas mostly are brought together in a packed column and can have either co-current or counter-current flows. For instance NH3 can be removed from its aqueous solutions by a counter current air flow in a packed column.

 

 

 

Top-Brine-Temperature TBT
Maximum temperature of the feed water in a desalination system, for instance right after the (feed) heater.

 

 

 

Total Dissolved Solids TDS
describes the content of all dissolved substances, organic as well as inorganic, in a liquid solution. The solutes can be contained in the solution in a molecular, ionized or micro- granular form. A micro-granular form stands for colloidal solutions with particles smaller than 2 mm.

 

 

 

Total Suspended Solids TSS

 

 



Total Organic Carbon TOC

 

 



Vacuum Membrane Distillation VMD, V-MEMD, MEVMD , MSVMD
Different from conventional Membrane Distillation (MD) systems, which have been characterised as diffusion-driven, evaporative processes, Vacuum Membrane Distillation (VMD) is a pure vaporisation process. This is due to the absence of Non-Condensable Gases or, in other terms, of a carrier gas establishing the evaporation process in the system. Thus, VMD is a real distillation process, making use of the vaporisation of pure water and subsequent condensation of water vapour in a condenser. The difference to other thermally driven processes is, that in VMD, vaporisation is established across a hydrophobic membrane, which basically serves as a containment for the feed water film or, in other terms, as vaporisation surface.

In the case of several stages or “effects”, the terms “Vacuum-Multieffect Membrane Distillation” (V-MEMD) [xxx_Zhao], “Multi-Stage Vacuum Membrane Distillation” (MSVMD) [xxx_Chung] or “Multi-Effect Vacuum Membrane Distillation” (MEVMD) [xxx_Kiefer] can be found in literature.

The separation of pure water and salt is due to a substantially lower vapour pressure of salt compared to water. At a given temperature, water will evaporate while salt is remaining dissolved in the liquid brine. Similar to all other thermal desalination processes, the fundamental driver of VMD is a net vapour pressure difference between feed water and condensate. This vapour pressure difference is induced by temperature differences between feed water and condensate, which are commonly generated by heating the feed water (addition of heat).

 

 

 

vaporisation, boiling
Vaporisation is a phase change from liquid to vapour (gas) at temperatures equal to or higher than its boiling temperature at a given pressure. Note that even in the scientific literature, the terms evaporation, boiling and vaporisation are frequently mixed up. In the present overview on desalination systems, the term “evaporation” stands for phase change phenomena at temperatures lower than the boiling point of a substance at a given pressure. Evaporation necessarily occurs in systems of three phases or more (e.g. liquid aqueous solution, water vapour and air) while in vaporisation, only two phases are involved (e.g. liquid aqueous solution and water vapour). In the present desalination compendium, the terms “boiling” and “vaporisation” are used in the same context.

 

 

vapour pressure pV
The pressure, at which a fluid starts to vaporise at a given temperature. The understanding of thermodynamic concepts around vapour pressure is crucial for the understanding of thermally driven desalination systems. Therefore, a deeper insight into the theory of vapour pressures is given in Annex C.

 

 

 

wetted area
The area in a humidifier or evaporator that is covered by a liquid film. The wetted area is often given as ratio of wetted to full heat exchanger area.


 

 

Zero Liquid Discharge ZLD
Zero Liquid Discharge in a desalination context is a water treatment process in which all fresh water is separated from a feed water stream and the remaining salts are recycled or deposited. Therefore, at the end of the treatment cycle, zero liquid discharge is arising. In fact, all desalination techniques listed in the present DME Technology Map can only achieve salt concentration values near the crystallisation limit. That is why the term “Near Zero Liquid Discharge” (NZLD) has become popular.

 

 


References (xxx in alphabetical order)



[1_arieh] Arieh, B.-N., Hydrophobic Interactions, Springer US, 1980, ISBN 978-1-4684- 3545-0.
[2_Chung] Chung, H.W., Swaminathan, J., Warsinger, D.M., Lienhard V, J.H., Multistage Vacuum Membrane Distillation (MSVMD) Systems for High Salinity Applications, Journal of Membrane Science, Vol. 497 (2016), pp. 128–141.
[3_chemie] Chemie.de, entry on “Hydrophilie”, last access 14-03-2019, http://www.chemie.de/lexikon/Hydrophilie.html
[4_Helle] Hellemans, M., The Safety Relief Valve Handbook – Design and Use of Process Safety Valves to ASME and International Codes and Standards, Elsevier Ltd., 2010, ISBN 978-1-85617-712-2.
[5_IDA] IDA Desalination Yearbook 2015 – 2016, ISBN: 978-1-907467-40-0.
[6_Kak] Kakaç, S., Liu, H., Heat Exchangers: Selection, Rating and Thermal Design, 2nd edition 2002, CRC Press, ISBN 0-8493-0902-6.
[7_Khayet] Khayet, M., Fouling and Scaling in Desalination, Desalination, Vol. 393 (2016), pp. 1–196.
[8_Kiefer] Kiefer, F., Spinnler, M., Sattelmayer, T., Multi-Effect Vacuum Membrane Distillation Systems: Model Derivation and Calibration, Desalination, Vol. 438 (2018), pp. 97–111.
[8_klein] Klein, H., Stoffübertragung, material to the lecture “Stoffübertragung”, Institute of Plant and Process Technology, Technical University of Munich, 2011.
[10_Millero] Millero, F.J., Feistel, R., Wright, D.G., McDougall, T.J., The composition of standard seawater and the definition of the reference-composition salinity scale, Deep-Sea Research I, vol. 55 (2008), pp. 50–72.
[xxxoxf1]
[xxx_Römpp]
[11_sat] Sattelmayer, T., Technische Thermodynamik – Energielehre und Stoffverhalten, Scriptum for the Lecture Thermodynamics I, Institute of Thermodynamics, Technical University of Munich, Mai 2012.
[12_Sharkawy] Sharqawy, M.H., Lienhard, J.H., Zubair, S.M., Thermophysical properties of seawater: a review of existing correlations and data, Desalination and Water Treatment, Vol. 16 (2010), pp. 354–380.
[13_Tapro] Taprogge GmbH, entry on “Tube Cleaning”, last access 04-03-2019, http://www.taprogge.com/products-and-services/in-ta-ct/tube-cleaning/index.htm
[14__Zhao] Zhao, K., Heinzl, W., Wenzel, M., Büttner, S., Bollen, F., Lange, G., Heinzl, S., Sarda, N., Experimental study of the memsys vacuum-multi-effect-membrane- distillation (V-MEMD) module, Desalination, Vol. 323 (2013), pp. 150–160.

Sunday, 05 May 2019 08:25

Microbial Desalination Cell (MDC)

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Microbial Desalination is a technology to remove salt ions from saline water (deionize saline water). Driven by electric current (electric potential difference) generated by the metabolic activity of exoelectrogenic microorganisms, i.e. driven by a bio-electric potential difference, ions are transported through ion selective membranes, thus generating an ion-enriched stream (brine) and an ion-depleted stream (desalinated water). Ion transport is effected in proportion to the electric current being generated by these microorganisms [1,2,3].

 

    1. Technical Description
    2. Plant Design
    3. Feed Water
    4. Desalinated Water & Brine
    5. Data and Information
    6. Preferred Use
    7. Environmental Impact
    8. Stage of Maturity
    9. Further Developments
    10. References

 




1. Technical Description



The Basics – Separation Principle and Operating Mechanism
An exoelectrogenic microorganism is a microorganism that has the ability to transfer electrons extracellularly. Exoelectrogenic microorganisms are also referred to as “exoelectrogens”, “electrochemically active bacteria”, “anode respiring bacteria” and “electricigens” [4]. A known species of exoelectrogens is, e.g., Geobacter sulfurreducens.

In a Microbial Desalination Cell (MDC) exoelectrogenic microorganisms serve to generate electric current (electrons) from oxidation of organic matter present, e.g., in wastewater [3] or in artificially created nutritious solutions. The electric potential difference between anode and cathode generated by the metabolic activity of these microorganisms is the driving force for desalination in an MDC. It is used to induce ion transport through ion exchange membranes [2,5], thus desalinating water.

Therefore, the driving force of desalination in MDC may be – more precisely – referred to as a “bio-electric” potential difference. The fundamental separation principle to separate ions from water in MDC is the capability of ions to move selectively according to their charge.

MDC is in nature similar to Electrodialysis (ED), yet different from ED because it does not require external electricity [1]. Instead, energy is provided by the exoelectrogenic microorganisms, being an integral part of the MDC.

It goes without saying that the particular attraction and benefit of MDC lies in the fact that MDC allows desalination without external electrical energy input and without the need of high feed pressure. In consideration of the relevance of energy cost in desalination, a desalination technology like MDC, which does not consume more energy than generated by itself, must be of particular interest.

A further benefit of Microbial Desalination Technology is that it combines at least two simultaneous functions: electrical energy production and desalination. Depending on design, it may also take up a third function. If, for example, wastewater is used to feed the MDC and the organics contained therein serve as food source for the microorganisms, the MDC can even achieve three functions simultaneously: energy production, desalination and wastewater treatment.

Process Description
The first proof of concept of MDC was demonstrated in 2009 by a 3-chamber configuration [1, 6, 7]. This basic Microbial Desalination Cell resembles a fuel cell, containing an anode and a cathode, between which a pair of ion selective membranes is inserted. Fig. 1 depicts the basic design of a Microbial Desalination Cell (MDC).

Fig. 1: MDC – basic design


It consists of three chambers:


1.    the anode chamber with an anion exchange membrane (AEM). Next to the anode a film of exoelectrogenic microorganisms is attached as a kind of biofilm. The chamber is typically filled with a liquid (e.g. wastewater) which contains nutrition for the exoelectrogenic microorganisms. These exoelectrogenic microorganisms oxidise organic matter, and, in doing so, release protons and electrons.
2.    the cathode chamber with a cation exchange membrane (CEM) positioned next to the cathode. This chamber, in which the electrons transferred from the anode are consumed by a chemical reduction reaction (as described below), is typically filled with a liquid that enhances cathode performance (e.g. water + air injection).
3.    the middle chamber between the two ion exchange membranes (AEM and CEM) is filled with feed water to be desalinated [1].

Process Description MDC
The MDC process (here with an air-cathode) is depicted in the following sequence (Fig. 2 A – C)

Fig. 2 A: MDC process - anode chamber     Fig. 2 B: MDC process - cathode chamber     Fig. 2 C: DC process - resulting stage

 

Exoelectrogenic microorganisms on the anode oxidise organic matter fed into the anode chamber. In doing so, they release protons (H+) and electrons (e-) (see Fig. 2 A). The following equation represents the oxidation reaction at the anode [8]:

(CH2O)n + nH2O → nCO2 + 4 ne- + 4nH+

The electrons (e-) leave the anode chamber and are transferred as electric current via external wire to the cathode. Protons (H+) cannot leave the anode chamber, as they are rejected on the anion exchange membrane (AEM). The surplus of positive charge in the anode chamber resulting from protons (H+) produced, however, desires balancing. The only source of balancing charge is drawing negatively charged ions (Cl-) through the AEM from the middle chamber into the anode chamber (see Fig. 2 A).
Simultaneously, in the cathode chamber, electrons (e-) are received as electric current (see Fig. 2 B). There they combine, e.g., with the oxygen provided by an air-cathode or by oxygen injection into the cathode chamber. They combine as well with the protons (H+) drawn from the liquid in the cathode chamber (chemical reduction reaction) to form H2O. The following equation represents the reduction reaction at the cathode [8]:

O2 + 4 ne- + 4nH+ → 2 H2O

The extraction of protons required for the formation of H2O leaves a deficit of positive charge in the cathode chamber which can only be replenished by attracting positively charged ions (Na+) from the middle chamber. As only positively charged ions can pass the cation exchange membrane (CEM), Na+ ions cross the CEM and replenish the protons consumed in the formation of H2O (see Fig. 2 B).

As a result (see Fig. 2 C), the feed water in the middle chamber is depleted of salt ions, i.e. desalted. Thus, the generation of electric current through oxidation activity of exoelectrogenic microorganisms induces an electric potential difference between anode and cathode, which in turn induces a selective ion transfer through the AEM and CEM, thereby depleting the feed water stream from salt ions.

This depletion of ions in the middle chamber results in water desalination without any water pressurisation or use of draw solutions or externally supplied electrical energy. Instead, energy is generated while water is desalinated, and, as the case may be, organic matter is removed from wastewater while being metabolised by the microorganisms ́ activity in the anode chamber [1, 2, 5, 6, 8, 9, 10].

MDC Process Peculiarities
-    MDC operation does not require electrical energy input and no elevated pressure level like Reverse Osmosis (RO) [1].
-    MDC requires, however, specific exoelectrogenic microorganisms which themselves need a continuous supply of a nutritious substrate for their metabolic work. MDC also requires an aerobic environment on the cathode side, which may be achieved by oxygen injection or otherwise procuring an aerobic water environment in the cathode chamber [6,8].
-    The supply of microorganism substrate may be secured by connecting the MDC to a wastewater plant effluent to benefit additionally from wastewater treatment as a co-performing element of the MDC process.
-    MDC may constitute a (limited) barrier against bacteria, viruses and other microbes as the pore sizes of ion exchange membranes used will be in the range of 1 nm (about 350 Dalton), i.e. considerably smaller than the size of viruses and bacteria [2]. However, contradicting this opinion, it should be noted that not the complete volume flow to be desalinated needs to pass through the ion exchange membranes, thus limiting the true sanitary impact of MDC technology.
-    Due to yet missing field experience, it is not known to what extent MDC modules might need intermittent cleaning during operation or to what extent they might need to be preserved against biological growth in case of shut down for a prolonged period.


For further requirements concerning MDC plant layout, please also refer to Section 2 (Plant Design) hereinafter.


Motivation of Use
In consideration of the remarkable energy cost of other desalination technologies, MDC has been developed to overcome this drawback [1]. The idea to desalinate water without consumption of energy is certainly fascinating. It requires, however, the integration of another process element (energy production by exoelectrogens from digesting organic matter). At this point of time, MDC has a unique potential to emerge as a technology to perform three fundamental tasks simultaneously: (seawater) desalination, electric energy generation and wastewater treatment [8].


Technical Variations
MDC Design Variation and Optimisation
The basic MDC cell, incorporating three chambers forming one stack, is illustrated in Fig. 1 above.

While this type of model will be indispensable for lab purposes, multiple stack designs are desirable to increase desalination volume and to decrease manufacturing cost. Multiple stack structuring is achieved by repetitive addition of AEM and CEM membrane pairs to the module as illustrated in Fig. 3 below, thus creating repeating desalting and concentration cells [7].

Fig. 3: Stack structure of MDC

 

Stacking increases the magnitude of ionic separation. In a stacked MDC, a single electron transfer from anode to cathode can separate as many ion pairs as the number of repeated AEM and CEM membrane pairs. For instance, in a 3 cell pair stack, a single electron transfer separates 3 pairs or mono-valent cations and anions by use of an (ideal perm-selective) ion exchange membranes [2,8].

Other basic design considerations in MDC technology relate to:
a) sizing of the anode surface in relation to cathode surface, whereby the cathode appears to require larger surfaces or a boost in speed of performance due to the relatively low speed of chemical reduction performance of the cathode;
b) sizing of the anode chamber volume versus the desalination chamber and cathode chamber volume. It appears that anode chambers require a significantly larger volume than the other chambers;
c) choosing optimum electrode materials, particularly for the cathode due to its slow chemical conversion characteristics. In this context, improved material choice for the purpose of elevated current densities per m2 of electrode surface is of particular interest [11];
d) choosing optimal electrode materials to improve electrode stability and lifetime.


MDC Operational Variations & Performance Optimisation
As MDC works with organic matter and may fulfil three tasks at once, there are numerous parameters to work on simultaneously. Research is on its way to study variations of parameters and analyse patterns of dependence. Yet, as MDC technology is relatively young, most current knowledge is based on lab tests. To the best of the author ́s knowledge, MDC field experience is still missing. Therefore, the following aspects of operation are of indicative nature and observations may yet not all be fully studied. Particular complexities are apparent when applying MDC:
-    A particular optimisation complexity of MDC is to understand the convergence or divergence of achieving three optimisation targets simultaneously, i.e. maximum electrical power generation, highest desalination volume or highest degree of desalination and highest reduction of organic matter.
-    A further particular complexity of MDC is to work with a multitude of parameters that may be altered and to understand their relative alteration contribution on the desired performance targets, both technically and commercially.

Some operational aspects, however, have been researched already in some detail and appear to have influence on MDC performance and its optimisation:
-    pH value variation between anode and cathode chamber: As the desalination cycles proceed, the pH value in the anode chamber decreases due to proton accumulation by microbial respiration and increases in the cathode chamber due to hydroxide accumulation by oxygen reduction [8]. Therefore, decrease in pH value is a major challenge for MDC operation [2]. It adversely affects both, the microbial activity and growth in the anode chamber and the chemical reduction efficiency of electron acceptors (O2) in the cathode chamber. Such pH imbalance may be alleviated by increasing the anodic chamber volume or by adding acid or base. The addition of acid or base as well as the addition of a phosphorous buffer solution do not appear feasible with respect to cost and environmental concerns. Furthermore, frequent exchange of the anolyte solution, i.e. the fluid contained in the anode chamber, has proven beneficial [6].
A recirculation of a fraction of the anolyte to the cathode chamber and from there back to the anode chamber, a so-called recirculation microbial cell (rMDC) design has been investigated to overcome the pH problem. As this solution generates new issues (e.g. transfer of O2 to the anode side), an economic and sustainable method of controlling the pH remains an urgent development need in MDC technology [6, 8].
-    Impact of Internal (Ohmic) Resistance: A decrease in conductivity of the saline feed water increases the internal resistance (IR), i.e. the resistance within the MDC cell and thus decreases the overall electric cell potential of the MDC. As a countermeasure, membrane distance may be increased to decrease IR [1, 6].

Also, stacking of MDC improves the desalination rate, but also leads to a higher electric potential loss due to an increase in IR from increased stacking [2, 6].

MDCs operated with lower Hydraulic Retention Time (HRT), i.e. the period until exchange of the anolyte, shows lower IR [6].
-    Impact of External (Ohmic) Resistance:
     The external resistance (ER), i.e. resistance in the wire between anode and cathode, is of importance for the desalination efficiency. At lower ER values (e.g. 10 Ohm instead of 100 Ohm), the electrical current density (in theory) is higher and thus increases the rate of desalination. In other words, more Total Dissolved Solids (TDS) is removed with lower ER (i.e. higher electrical current density) [6].
-    Batch vs. continuous MDC operation:
     In batch mode, the performance of MDCs decreases with time as the internal resistance (IR) increases due to the lowering of electrolyte conductivity in the desalination chamber. Cyclic batch mode, or even better, continuous mode operation can be the optimum choice for practical operations because it reduces total capital cost and facilitates control of decisive parameters such as pH and substrate concentration [6].
-    Variation of Hydraulic Retention Time (HRT):
     MDCs operated with lower HRT of anolyte solution exhibit lower Internal Resistance (IR) [6, 12].
-    Scaling of CEM membranes and fouling of AEM membranes:
     Depending on the salinity of the water to be desalinated, CEM scaling is of significant importance for MDC performance [6, 7]. A complete prevention of membrane scaling appears impossible; however, use of an oxygen cathode with acidified water may alleviate scaling [7]. Membrane fouling may be observed on AEM due to biofilm growth [5, 6]. Chosen ion exchange membranes also differ considerably in pore size, degree of organic matter.
-    Choice of exoelectronic microorganisms:
     It will be obvious that the metabolism of microorganisms differs from species to species. Therefore, study of MDC performance in terms of electron generation capabilities and degradation potential of organic matter are relevant areas of study [13].

Differences to and Similarities with other Relevant Technologies
The MDC process has great similarity with Electrodialysis (ED), but in the case of ED external electrical energy is used to provide energy for the separation of ionic species.
With respect to Reverse Osmosis (RO), MDC does not need pressure elevation to high levels.
However, different to all other desalination technologies, MDC integrates bio-electrochemical energy production with desalination and water treatment, i.e. performs multiple functions. Due to this specialty, a one to one comparison of MDC to other (pure) desalination technologies is not advisable, also because the technologies have different outputs.

A further comparison of benefits and drawbacks vis à vis other desalination technologies appears premature due to the fact that MDC does not yet have practical field experience for realistic comparison.


 




2. Plant Design


Process Requirements
A full plant arrangement may - apart from the core desalination unit (MDC) - also require the following:
-    A feed pump for supplying pretreatment and desalination unit with feed water is needed.
-    Appropriate pretreatment to limit scaling and fouling of MDC desalination chambers with elevated scaling risk seems to be necessary.
-    Appropriate process treatment to reduce scaling potential, particularly on CEM membranes, appears necessary.
-    Depending on finally preferred channel width of the desalination chamber (e.g. 0.3 – 1.5 cm) and the preferential widths of anode and cathode chambers, the MDC cell requires some specific degree of protection against blocking by particles which may differ for the three chambers into which fluids are fed. Particle filters in the range of a few microns could serve as the last step of pretreatment for the feed water to be desalinated, for the influent water from waste water treatment process to be fed to the anode chamber as well as for the liquid in the cathode chamber [6].
-    Depending on application, the feed water streams may need further individual pretreatment to protect the micron filtration systems suggested beforehand (e.g. further pre-filtration step at larger mesh size).
-    Depending on Total Suspended Solids and Total Organic Carbon (TSS/TOC) loading of the feed water, further pretreatment to reduce TSS/TOC volume may be required for the feed water to be desalinated; also, the TSS/TOC levels of the anolyte and catholyte need separate specification.
-    In applications with elevated scaling risk, appropriate process treatment to reduce scaling potential, particularly on CEM membranes, appears necessary.
-    Compressed air injection may be required for optimised cathode performance.
-   Cleaning-in-Place (CIP) unit (possibly with neutralisation) for cleaning of MDC modules may be a requirement.
-    A wastewater disposal facility to allow for occasional CIP wastewater discharge (if in fact required), intermittent filter backwash water discharge and sludge discharge for used up anolyte discharge may be needed.
-    Depending on application, posttreatment of the desalinated water may be required.

MDC Plant Layout
Due to the advantage of being able to build MDC units module based, MDC plants are scalable in size [3]. Fig. 4 illustrates an exemplary MDC system arrangement.

Fig. 4: Exemplary MDC system arrangement (in conjunction with wastewater treatment plant)


 




3. Feed Water



1.    Different from other desalination technologies, three feed streams need to be considered: the feed flow of the water to be desalinated, the wastewater treatment flow connecting to the anode chamber and the water flow feeding the cathode chamber.
2.    Without any field experience so far, it is premature to take a judgement on the potential techno-commercial limitations of MDC due to the level of feed water salinity of the water to be desalinated.
3.    As far as other pretreatment requirements are concerned, please refer to the points mentioned hereinabove.
4.    Temperatures may be limited to AEM and CEM operational limits, possibly also to anode and cathode temperature limitations.
5.    For general guidance purpose, the following Table 1 characterises general MDC feed water limits for the water to be desalinated.

 

Feed Water Salinity Technically feasible Now in Use for Desalination Potentially for techno-commercial Viability for the Future

> 100,000 ppm
(highly concentrated Brine)

     

50,000 – 10,0000 ppm
(Brine)

     

10,000 – 50,000 ppm
(Seawater)

 X    X

1,000 – 10,000 ppm
(Brackish Water)

X    X

< 1,000 ppm
(Fresh Water)

   X

Table 1: Stage of development of MDC technology in relation to water salinity [2, 6]

 

Because of the comparatively low desalination efficiency for high-salinity water, one potential application of MDC technology could be brackish water desalination [6].

 

 

 

 


4.    Desalinated Water & Brine



Without any field experience so far, it is premature to characterise desalinated water and discharge flows in volume or quality other than recognising their existence as depicted in Fig. 4 above.

 

 

 


5.    Data and Information



In the absence of field test results so far, it does not appear appropriate to take assumptions on data and information under this chapter.

 

 

 

 


6.    Preferred Use



The techno-commercial feasibility of MDC has not yet been demonstrated in the field. Therefore, the preferred uses listed below are of indicative nature only:
1.    Seawater desalination
       Lab tests vary widely < [1,9] but show up to 99 % salinity removal depending on Hydraulic Retention Time (HRT) [6].
2.    Brackish water desalination
       An obstacle of low salinity desalination by MDC is that the low conductivity increases the internal resistance on the MDC. This disadvantage may be overcome by adding an ion exchange resin to the desalination chamber. Also, salt removal from the desalination channel increases the salinity of the anolyte which may negatively affect the activity level of the microbial community in the anode chamber [6].
3.    Water softening
       Up to 90 % hardness removal has been demonstrated in lab tests [6].
4.    Ground water remediation (in particular nitrate removal) may be a feasible application [6].
5.    Simultaneous desalination, wastewater treatment and hydrogen production (while adding energy to an MDC process in a modified “Microbial Electrolysis and Desalination Cell”) may be a desired application [6].


 

 

 


7.    Environmental Impact



With respect to energy consumption the MDC may be considered a sustainable process, as it is based on a renewable primary energy source. However, research has not yet demonstrated dependable field test results to judge environmental impacts of MDC professionally.

Also, and as mentioned above, it appears likely from lab test demonstrations that MDC will not be able to survive without countering measures of scaling and fouling. In this respect dosing of chemical additives is very likely to be required to maintain MDC performance.

 

 

 


8.    Stage of Maturity



Table 2 summarises MDC technology with respect to the technology ́s stage of maturity.

1 2 3 4 5
Basic R&D

Prototyping/
Lab Tests

Field Tests/
Demonstration
Commercialization (up to 7 years) Use/Established
(more than 7 years)
   X      

Table 2: Stage of maturity of MDC technology

 





9.    Further Developments



These are the challenges for improvement in MDC:
1. Primary target for MDC will be to reach field test level to measure and benchmark real performance and to generate cost reduction from exploiting scale effects [14].
2. Scaling up of MDC devices will be a further target. While primary tests have been performed with desalination chambers of 3 ml, larger desalination chambers (15 litres) are subject of more recent investigation. Simultaneously the anode chamber has been increased from 27 ml to 60 litres. The largest MDC (total volume of 105 litres) has achieved an electricity generation of 2,000 mA and a salt removal rate of 9.2 kg/m3/d [6, 14].
3. For developing more breadth and depth in applications, it is envisioned that MDC may be used as pretreatment of RO systems to reduce the overall cost of desalination [6]. In particular, the energy produced in MDC operation could be used to run downstream RO or Electrodeionisation (EDI) plants.
4. Major challenges for the development of MDC as a desalination technology are:
   - managing pH variations;
   - managing scaling and fouling, in particular cathode scaling;
   - controlling internal and external resistance;
   - improving anode and cathode materials and longevity;
   - improving exoelectrogenic bacteria performance.



 

 


10. References



[1] Cao, Xiaoxin; Huang, Xia; Liang, Peng; Xiao, Kang; Zhou, Yingjun; Zhang, Xiaoyuan; Logan, Bruce E.: A New Method of Water Desalination Using Microbial Desalination Cells. Environmental Science & Technology 43 (2009), pp. 7148-7152.
[2] Kim, Younggy; Logan, Bruce E.: Microbial desalination cells for energy production and desalination. Desalination 308 (2013), pp. 122-130.
[3] Subramani, Arun; Jacangelo, Koseph G.: Emerging desalination technologies for water treatment: A critical review. Water Research 75 (2015), pp. 164-187.
[4] Logan, Bruce: Exoelectrogenic bacteria that power fuel cells. Nature Reviews Microbiology 7 (2009), pp. 375-383.
[5] Wang, Heming; Ren, Zhiong Jason: A comprehensive review of microbial electrochemical systems as a platform technology. Biotechnology Advancs 31 (2013), pp. 1796-1807.
[6] Sevda, Surajbhan; Yuan, Heyang; He, Zhen; Abu-Reesh, Ibrahim M: Microbial desalination cells as a versatile technology: Functions, optimization and prospective. Desalination 371 (2015), pp. 9-17.
[7] Barastad, Kristen S.; He, Zhen: Water softening using microbial desalination cell technology. Desalination 309 (2013), pp. 32-37.
[8] Saeed, Henna M., Husseini, Ghaleb A.; Yousef, Sharifeh; Saif, Jawaria; Al- Asheh, Sameer; Abu Fara, Abdullah; Azzam, Sara; Khawaga, Rehab; Aidan, Ahmed. Microbial desalination cell technology: A review and a case study. Desalination 359 (2015), pp. 1-13.
[9] Luo, Haiping; Xu, Pei; Roane, Timberley M., Jenkins, Peter E., Ren, Zhiyong: Microbial desalination cells for improved performance in wastewater treatment, electricity production, and desalination. Biosource Technology 105 (2012), pp. 60-66.
[10] Asadi-Ghalhari; Mehrdadi, Nassar; Nabi-Bidhendi, Gholamreza: Simultaneous Desalination of Was water and Electricity Production with New Membrane Technolgoy, Air-Cathode Microbial Desalination Cells. Current World Environment, Vol. 10(1) (2015), pp. 115-120.
[11] Sharma, Mohita; Bajracharya, Suman; Gildemyn, Sylvia; Patil, Sunil A.; Alvarez-Gallego, Yolanda; Pant, Deepak; Rabaey, Korneel; Dominguez-Benetton, Xochtil: A critical revisit of the key parameters used to describe microbial electrochemical systems. Electrochimica Acta 140 (2014), pp. 191- 208.
[12] Qu, Youpeng; Feng, Yujie; Liu, Jia; He, Weihua; Shi, Xinxin; Yang, Qiao; Lv, Yiangwei; Logan, Bruce: Salt removal using multiple microbial desalination cells under continuous flow conditions. Desalination 317 (2013), pp. 17-22.
[13] Logan, Bruce: Bioenergy production using microbial fuel cells. Presentation posted on YouTube Jan. 6, 2016. URL: https://youtube/x-iN-O89TNA (Stand 21.08.2017)
[14] Zhang, Fei; He, Zhen: Scaling up microbial desalination cell system with a post-aerobic process for simultaneous wastewater treatment and seawater desalination. Desalination 360 (2015), pp. 28-34.

Monday, 22 May 2017 12:49

Adsorption

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Adsorption is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation:

Monday, 22 May 2017 12:29

Electrosorption

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Electrosorption is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation:

Monday, 22 May 2017 12:24

Desorption

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Desorption is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation:

Monday, 22 May 2017 12:18

Sorption

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Sorption is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation:

Monday, 22 May 2017 12:09

Electrical Double Layer (EDL)

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Electrical Double Layer (EDL) is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation:

Monday, 22 May 2017 11:48

Feed Water

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Feed Water is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation:

Monday, 22 May 2017 11:45

Brackish Water

Written by
  1. Technical Description
  2. Plant Design
  3. Feed Water
  4. Desalinated Water & Brine
  5. Data and Information
  6. Preferred Use
  7. Environmental Impact
  8. Stage of Maturity
  9. Further Developments
  10. References

1. Technical Description


 

Brackish Water is a technology to remove ions from water by applying an electrical voltage difference between two porous carbon electrodes, in which ions will be temporarily stored.

CDI is a technology also known as Electrochemical Demineralization 〈1〉 or as Electrosorption 〈2〉. CDI's preferred use is in low salinity desalination applications (in principle below 10,000 ppm (1), in practice below 4,000 ppm (4)), where the benefit is lower energy consumption and higher recovery rates in comparison to Reverse Osmosis (RO) or distillation as alternative methods of brackish water desalination. This is mainly because CDI removes only salt ions, i.e. a tiny mass, from the salty feed water, whereas in RO or distillation a massively larger mass of water is removed from the salty feed water (1).

 

2. Plant design


 

The humidification dehumidification (HD) process uses the temperature dependence of the vapour pressure of water in air. The vapour pressure of water in air at saturation rises exponentially with the temperature. The dependence can be approximated e.g. by the Antoine equation: