Water Desalination G22222222222 (MF).pptx
Water Desalination G22222222222 (MF).pptx
- 1. Prepared By :-
Mohamed Fathy Gamal
Abdelrahman Abd-Elmoamen
Supervised By :-
Prof.Dr :-
Eman Ashour
Minia University
Faculty of Engineering
Chemical Engineering Department
Fourth Year 9/03/2024
Water Desalination Cont. - 3. Electrodialysis reversal utilizes a
membrane, like that in reverse
osmosis, but sends an electric
charge through the solution to draw
metal ions to the positive plate on
one side, and other ions (like salt)
to the negative plate on the other.
Electro dialysis ( ED ) - 4. Electrodialysis is a process for the
separation of electrolyte from a
solvent,typically water .
The process is widely used in the
desalination of water and process
solutions .
it uses a direct electrical current to
transport ions through sheets of ion-
exchanger membranes and is
operated in a unit with at least three
compartments .
The terminal compartments house an
anode and a cathode , between which
a potential difference is applied to
drive the ions through the electrolyte
solutins and the membranes .
Process - 5. Two types of membranes are used : one which is perferentially ,
permeable to the transport of anions (anion-selective) , and one
which is perferentially permeable to cations (cation-selective).
Membranes are arranged alternately between the electrodes ,
forming individual compartments (or cells).
The solution to be desalinated is held in one compartment and
during current flow , anions move through the anion exchange
membrane in the directon of the anode into adjacent compartment
cations move in the opposite direction into an adjacent
compartment on the other side .
Thus , overall , the solutions becomes depleted in ions in one
compartment and solutions in adjacent compartment become
enriched in ions .
In practice , solutions flow through the compartment to allow
continuous operation and several hundred cell pairs (one
concentrated and one diluted solution are used).
Cont…. - 6. How does ED works ?
Cations (Na+) attraction pairs of Water molecules break down
(dissociate) at the cathode to produce two hydroxyl (OH-)ions plus
hydrogen gas (H2) , hydroxide raises the pH of the water . - 7. ED vs RO
Electrodialysis (ED) Reverse Osmosis (RO)
ED is a voltage driven process RO is a preasure-driven process
Electrodialysis is usually applied to
deionization of aqueous solutions
RO is used to remove suspended
solids , total organic carbon (TOC) ,
or other contaminants
Sometimes pre-treatment is
necessary
pre-treatment is necessary
always
High conversion ratio (nearly 80%) Low conversion ratio (30 to 80 %) - 8. Advantages Disadvantages
Low energy consumption Only removes ions : organics and
colloids not removed
High conversion ratio Selectyion of membranes and stacks
highly dependent on feed water
chemistry
Low space and material requirements Purity affected by quality of feed water
The product water needs only limited
pretreatment
Contro required for optimum condition
Higher brine concentration achievable
ED - 9. Capacitive deionization (CDI) including membrane CDI
(MCDI) is an emerging technology for seawater and brackish
desalination
CDI is a different type of desalination Process that remove
ions from the saline water stream at atmospheric pressure
using direct current (DC) power
Electrodes become positively and negatively charged when
DC power applies to CDI electrodes
During CDI operation , ions in saline water are adsorbed on
the cathode and anode
After that ions are desorbed from the electrodes by
discharging of CDI
CDI is operated by the charging and discharging process to
produce freshwater
Capacitive Deioniztion (CDI) for desalination of brackish
water - 11. Advantages of CDI
Energy efficiency
Cost-effectiveness
High rejection ratio
Disadvantages of CDI
The commercialization of CDI is limited due to lack of
suitable materials for electrodes - 12. Basic Principles of Ion Exchange
Ion exchange resin is an insoluble, porous, polymer bead.
The beads have a very high molecular weight and carry a
functional group with either positive (+) or negative (-) charge,
known as exchange sites.
Negatively charged resin is called cation resin and attracts positive
ions, or cations.
Positively charged resin is called anion resin and attracts negative
ions, or anions.
The strength and characteristics of the exchange sites, determine a
resin’s affinity for certain ions.
For example, ions with multiple charges, (e.g. Ca++) have a
stronger attraction to the resin than ions with single charges.
Ions of equal charge are selected by the resin based on molecular
weight.
Heavier ions are selected first. Basic water softening theory
originated from this principler.
Ion Exchange Resin (IER) - 13. Types of
Ion
Exchange
Cation exchange resin
can be divided into two
A-Highly acid cation exchangers
B-Slightly acid cation exchangers
Anion Exchange Resin
Can be divided into two
A-Low alkalinity anionic
exchangers
B-High alkalinity ion exchangers - 15. Cation Exchange Resins vs. Anion Exchange Resins
Cation Exchange Resins Anion Exchange Resins
exchange positive ions exchange negative ions
Common cations include Ca+2, Mg+2,
Fe+2, and H+1
Common anions include Cl-1, SO4-2, and
OH-1
both types are similar and belong to a
group of compounds called polymers
both types are similar and belong to a
group of compounds called polymers - 16. Water Deionization
ions and make up a large portion of the pollutants in water.
These pollutants are efficiently separated from the water as
it passes through the deionized system, resulting in clean,
purified water.
Water travels through two kinds of ion-exchange resin,
which replace positively and negatively charged particles
with hydrogen (H+) and hydroxyl (OH-) ions.
Theoretically, the deionization process can eliminate all
remnants of salt from water. In fact, deionized water can also
be free of potentially dangerous elements such as viruses,
germs, and organic matter. DI water systems softens the
water by removing the ionized particles, sodium, and
replacing them with hydrogen. - 17. The FO process results in concentration of a feed stream and
dilution of a highly concentrated stream (referred to as the
draw solution).
Forward Osmosis (FO)
Forward osmosis membranes are of the asymmetric composite type-
• active layer (typically 100-200nm in thickness)
• support layer (typically 100-200μm in thickness) - 18. The general equation describing water transport in FO, RO, and
PRO is Jw = A(σ π − ∆P)
where Jw is the water flux,
A the water permeability constant of the membrane,
σ the reflection coefficient
∆P is the applied pressure. In FO ∆P = 0
The reflection coefficient describes the ability of a membrane active
layer to preferentially allow solvent permeation over solute
permeation
σ = 𝒋𝒘,𝒆𝒙𝒑 / 𝒋𝒘,𝒑𝒓𝒆𝒅 - 19. Membrane Modules in Forward Osmosis
Modules Packing density Advantages disadvantages
Plate and frame below 100
m2/m3
ease of operation in case of
high amounts of fouling agents
large footprint
Spiral wound up to 600 m2/m3 suitable for large volume
applications due to high
packing density
membrane fouling
Tubular up to 500 m2/m3 ease of cleaning, replacement
and ease of operation
tube wall thickness
might limit the water
flux performance
Hollow up to 1600
m2/m3
Ideally suitable for high
volume applications
prone to fouling with
high solid loadings - 20. MODERN APPLICATIONS OF FORWARD OSMOSIS
Waste water treatment and water purification
Seawater desalination
Food processing
Pharmaceutical industry
Editor’s Notes
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
- Scarcity of fresh water has serious implications. It can slow or stop economic expansion, reduce agricultural output, hamper food independence, and degrade public health and quality of life.
