30 Questions
What does Electrodialysis (ED) remove from water?
Ions
What is the current density in the given context?
50 A/cm2
What type of water is Electrodialysis (ED) particularly adapted for deionization?
Brackish water
What is one of the limitations of Electrodialysis for deionization?
High energy consumption for freshwater
What is the volume if the detention time is 10 seconds and the flow rate is 4000 m3/d?
400 m3/s
What is the relationship between the electrical energy required in Electrodialysis and the amount of salts removed?
Directly proportional relationship
What is the driving force in Electrodialysis?
Electromotive force
What type of membranes are used in Electrodialysis to separate ionic components?
Semipermeable ion-selective membranes
Which electrode attracts positively charged ions in Electrodialysis?
Cathode
What happens to anions in Electrodialysis?
Migrate towards the Anode
What is the main difference between Electrodialysis and technologies like RO, MF, UF, and NF?
Driving force used
In Electrodialysis, what type of membrane allows cations to pass but not anions?
Cation-permeable membrane
What is the term used to describe the amount of chlorine needed to oxidize the materials in water?
Chlorine demand
What does the free residual chlorine consist of?
HOCl and OCl
At what point in the chlorine addition process does free residual chlorine start to appear in water?
At the breakpoint (point C)
Which term describes the residual between points A to C where the chlorine is in the form of chloramines and chloro-organics?
Combined residual
What does the total residual after the breakpoint represent?
The sum of free and combined residuals
What does the break point, referred to in the text, signify?
The point where free residual chlorine appears
What is the function of high pressure in liquefying Cl2 gas?
To decrease the temperature
In the presence of water, what does chlorine gas react to form?
Hypochlorous acid
At which pH and temperature conditions is HOCl more effective than OCl-?
Higher pH and lower temperature
What does the sum of the concentration of hypochlorous acid and hypochlorite ion represent?
Free chlorine residual
How is the effectiveness of compounds containing chlorine evaluated?
By comparing percent of actual chlorine with percent of available chlorine
What type of compounds can reduce chlorine to the non-effective chloride ion ClǦ?
Iron (Fe)
What is the valence change of chlorine species in chlorine dioxide?
+4 to -Ѹ1
What are the products formed when NH2Cl reacts with 2HOCl?
NHCl2 and H2O
What are trihalomethanes (THMs) commonly produced from?
Organic matters
At what point in the chlorine dosage-residual chlorine graph does the reaction with reducing compounds occur?
At point A
What is the maximum acceptable concentration of total trihalomethanes (THMs) in drinking water?
0.1 mg/l
What happens beyond point B on the chlorine dosage-residual chlorine graph?
Oxidation to nitrogen gas
Study Notes
Electrodialysis (ED)
- Removes ions from water, not bacteria, viruses, uncharged molecules, or suspended solids
- Suitable for deionization of brackish waters with TDS ≤ 5000 mg/L to produce product water with TDS ≈ 500 mg/L
- Not well-suited for deionization of seawater due to high energy consumption
- Electrical energy required is directly proportional to the amount of salts removed
Chlorine Compounds
- Both HOCl & OCl- react with ammonia to produce chloramines (monochloramine, dichloramine, and trichloramine)
- Both HOCl & OCl- react with reducing compounds (Fe+2, Mn+2, NO2-) to reduce chlorine to non-effective chloride ion Cl-
- Both HOCl & OCl- react with natural organic matter to produce trihalomethanes (THMs), which are carcinogenic compounds
- Total concentration of THMs in drinking water should not exceed 0.1 mg/L
Breakpoint Chlorination
- Chlorine dosage is added to water, reacting first with reducing compounds, then with NH3 to form chloramines
- Further addition of chlorine oxidizes chloramines to nitrogen gas and reduces chlorine to non-effective Cl- ion
- Continued addition of chlorine produces free available chlorine, which appears after the breakpoint (point C)
- Free residual = dosage - demand, where demand is the amount used to oxidize materials existing in water
- Total residual = free residual + combined residual
Example Problems
- Calculates the current density, required area, and volume of one cell given an ED stack and detention time
- Calculates the salts concentration in product water and disposed concentrate water using mass balance application on the ED stack equations
Learn about the principles of Electrodialysis, a membrane treatment method driven by electromotive force. Discover how it differs from other technologies like RO, MF, UF, and NF. Explore the separation of ionic components using semipermeable ion-selective membranes.
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