University of Babylon - Chemical Engineering: Electrodialysis Treatment
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Questions and Answers

What does Electrodialysis (ED) remove from water?

  • Viruses
  • Bacteria
  • Suspended solids
  • Ions (correct)

    • What is the current density in the given context?

  • 50 A/cm2 (correct)
  • 10 A/cm2
  • 100 A/cm2
  • 500 A/cm2

    • What type of water is Electrodialysis (ED) particularly adapted for deionization?

  • Seawater
  • Freshwater
  • Mineral water
  • Brackish water (correct)

    • What is one of the limitations of Electrodialysis for deionization?

    <p>High energy consumption for freshwater</p> Signup and view all the answers

    What is the volume if the detention time is 10 seconds and the flow rate is 4000 m3/d?

    <p>400 m3/s</p> Signup and view all the answers

    What is the relationship between the electrical energy required in Electrodialysis and the amount of salts removed?

    <p>Directly proportional relationship</p> Signup and view all the answers

    What is the driving force in Electrodialysis?

    <p>Electromotive force</p> Signup and view all the answers

    What type of membranes are used in Electrodialysis to separate ionic components?

    <p>Semipermeable ion-selective membranes</p> Signup and view all the answers

    Which electrode attracts positively charged ions in Electrodialysis?

    <p>Cathode</p> Signup and view all the answers

    What happens to anions in Electrodialysis?

    <p>Migrate towards the Anode</p> Signup and view all the answers

    What is the main difference between Electrodialysis and technologies like RO, MF, UF, and NF?

    <p>Driving force used</p> Signup and view all the answers

    In Electrodialysis, what type of membrane allows cations to pass but not anions?

    <p>Cation-permeable membrane</p> Signup and view all the answers

    What is the term used to describe the amount of chlorine needed to oxidize the materials in water?

    <p>Chlorine demand</p> Signup and view all the answers

    What does the free residual chlorine consist of?

    <p>HOCl and OCl</p> Signup and view all the answers

    At what point in the chlorine addition process does free residual chlorine start to appear in water?

    <p>At the breakpoint (point C)</p> Signup and view all the answers

    Which term describes the residual between points A to C where the chlorine is in the form of chloramines and chloro-organics?

    <p>Combined residual</p> Signup and view all the answers

    What does the total residual after the breakpoint represent?

    <p>The sum of free and combined residuals</p> Signup and view all the answers

    What does the break point, referred to in the text, signify?

    <p>The point where free residual chlorine appears</p> Signup and view all the answers

    What is the function of high pressure in liquefying Cl2 gas?

    <p>To decrease the temperature</p> Signup and view all the answers

    In the presence of water, what does chlorine gas react to form?

    <p>Hypochlorous acid</p> Signup and view all the answers

    At which pH and temperature conditions is HOCl more effective than OCl-?

    <p>Higher pH and lower temperature</p> Signup and view all the answers

    What does the sum of the concentration of hypochlorous acid and hypochlorite ion represent?

    <p>Free chlorine residual</p> Signup and view all the answers

    How is the effectiveness of compounds containing chlorine evaluated?

    <p>By comparing percent of actual chlorine with percent of available chlorine</p> Signup and view all the answers

    What type of compounds can reduce chlorine to the non-effective chloride ion ClǦ?

    <p>Iron (Fe)</p> Signup and view all the answers

    What is the valence change of chlorine species in chlorine dioxide?

    <p>+4 to -Ѹ1</p> Signup and view all the answers

    What are the products formed when NH2Cl reacts with 2HOCl?

    <p>NHCl2 and H2O</p> Signup and view all the answers

    What are trihalomethanes (THMs) commonly produced from?

    <p>Organic matters</p> Signup and view all the answers

    At what point in the chlorine dosage-residual chlorine graph does the reaction with reducing compounds occur?

    <p>At point A</p> Signup and view all the answers

    What is the maximum acceptable concentration of total trihalomethanes (THMs) in drinking water?

    <p>0.1 mg/l</p> Signup and view all the answers

    What happens beyond point B on the chlorine dosage-residual chlorine graph?

    <p>Oxidation to nitrogen gas</p> Signup and view all the answers

    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

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    Description

    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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