SLIDE 1
Capacitor
Conducting plate (Al foil) Electrodes Dielectric
+ + + + + + + +
- +
+ + + + + + +
- +
capacitive deionization (CDI) approach Htet Hte Kyaw - - PowerPoint PPT Presentation
capacitive deionization (CDI) approach Htet Hte Kyaw - - PowerPoint PPT Presentation
Brackish water desalination using capacitive deionization (CDI) approach Htet Hte Kyaw Nanotechnology Research Centre Sultan Qaboos University Seminar on "Small Desalination Units for Agriculture Sustainability, (Challenges &
SLIDE 2
SLIDE 3
Desalination
Desalination grew from 3% of total water supply in 1999 to 13% in 2008 RO desalination is the main desalination technology used
SLIDE 4
Energy Consumption
Energy Requirement RO CDI Electrical (kWh/m3) 2 < 1 Acceptable salinity level for different applications
Irrigation & industrial cooling system – 1000 to 3000 ppm Household use – up to 1000 ppm Safe drinking water – less than 150 ppm Industrial level (high end product) – less than 5 ppm § Only ions can be removed § High energy consumption for high salinity water
Some limitations Main advantages of CDI technology
CDI exhibit less fouling No electrode deterioration No pressure required Less energy
SLIDE 5
Sea Water Intrusion
Well pumping fresh water Salt water Fresh groundwater Ocean Well pumping salty water Sea water intrusion Cone of depression
- 65% of fresh water (ground water) available in Oman
- Increased demand combined with falling water tables lead
to rapid seawater intrusion.
After pumping by many wells
SLIDE 6
(Oman Salinity Strategy. In Ministry Of Agriculture And Fisheries: Sultanate of Oman, 2012)
Sea Water Intrusion
- Al Batinah region accounts
for >50% of Oman’s agriculture
- Rapid population growth &
increased agricultural activities
- Salinity increased due to
sea water intrusion
2,000 km of coastline
SLIDE 7
Capacitive Deionization
+ + + + + + + + + +
- - - - - - - - - -
Electrode Electrode
Saline water Electrochemical controlled technique to remove ions by applied potential Higher surface area Higher ions adsorption Anion (Cl -) Cation (Na +) Electrosorption process
Desalination process
200 400 600 800 1000 1200 0.05 0.10 0.15 0.20 0.25
conductivity (mS/cm)
time (s)
SLIDE 8
+ + + + + + + + + +
- Electrode
Electrode Regeneration process
Anion Cation
+ + + + + + + + + +
- Brine solution (Out)
Capacitive Deionization
Higher surface area Higher ions adsorption Electrosorption process
1400 1600 1800 2000 2200 2400 2600 2800 3000 0.05 0.10 0.15 0.20 0.25 0.30
conductivity (mS/cm)
time (s)
SLIDE 9
CDI cell structure
100 m
Current collector Acrylic plate Activated carbon cloth Activated carbon cloth Spacer Acrylic plate Current collector Inlet Outlet
Specific surface area – 1043 m2/g pore volume – 1.417 cm3/g Mean pore diameter – 0.7 nm & total pore volume – 1.417 cm3/g
FM-100 ACC Zorflex
SLIDE 10
Results
► Synthetic Brackish water – 1, 3 and 5 g/l ► Desalination cycle – 17 min
Effect of salt concentration on desalination by synthetic water
► Feed water salinity increased Desalination efficiency decreased ► Rate of salt adsorption increased
SLIDE 11
Synthetic water Vs Brackish water (from a well in Al Musanaah)
Results
Sample Desalination efficiency (%) Power consumption (kWh/m3) Electrode salt adsorption capacity (mg/g) Synthetic water 32 0.85 10.5 mg/g Well water 27 0.75 8.9 mg/g
SLIDE 12
Ion Selectivity
Results
- Divalent species like Ca2+ preferentially adsorb over the monovalent
species
- Higher K+ removal efficiency due to lower concentration in well water
SLIDE 13
Results
Disinfection properties
Bacterial electroadsorption on ACC surface
Electrode surface creates a hypertonic environment Dehydration of cells lead to cell death 3-fold reduction in bacterial colonies after desalination Electroadsorption is dominant mechanism
- f disinfection
- K. Luxman et al., Desalination 362 (2015) 126-132
SLIDE 14
14
Results
- Desalination trends over a period of 1 day for brackish water and synthetic
water of similar conductivity
- 0.01 M citric acid (pH 2.96) followed by 0.01 M NaOH cleaning after 24
hours of operation
Long term desalination and electrode regeneration
SLIDE 15
15
Conclusions
- Brackish water was successfully treated using CDI
- Brackish water power consumption was marginally lower
(0.78 kWh/m3) compared to synthetic water (0.85 kWh/m3)
- Disinfection properties mainly attributed to
electroadsorption of microbes
- Scale forming ions (Ca2+) is efficiently removed during the
process
- Electrodes were completely regenerated after cleaning
leading to repeatable desalting capabilities
SLIDE 16
16
Nanotechnology Research Centre The Research Council of Oman (TRC) Sultan Qaboos University Acknowledgements
SLIDE 17
17