RO Membrane Process for Salt Content Equalization
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Questions and Answers

What is the purpose of applying pressure in Reverse Osmosis?

  • To increase the salt content in the water product
  • To reduce the osmotic pressure of the salt solution
  • To increase the surface area of the membrane
  • To prevent water flow from the side of higher salt content (correct)

    • What is the primary function of the membrane in Reverse Osmosis?

  • To block salt ions and allow water passage (correct)
  • To block both salt ions and water passage
  • To allow both salt ions and water passage
  • To block water passage and allow salt ions to pass through

    • What is the ratio of water product to feed in a Reverse Osmosis system for seawater?

  • 90% of feed
  • 70% of feed
  • 50% of feed
  • 30% of feed (correct)

    • What is the primary material used in the manufacture of Reverse Osmosis membranes?

    <p>Cellulose acetate</p> Signup and view all the answers

    What is the factor that determines the scaling potential in a Reverse Osmosis system?

    <p>Concentration of ions in the brine</p> Signup and view all the answers

    What is the purpose of the reject stream in a Reverse Osmosis system?

    <p>To concentrate the salt ions</p> Signup and view all the answers

    What is the definition of atomic weight?

    <p>The weight of an element relative to C-12</p> Signup and view all the answers

    What is the primary function of a coagulant in water treatment?

    <p>To reduce the net electrical repulsive forces at particle surfaces</p> Signup and view all the answers

    What is the formula of Aluminum Sulfate (filter Alum)?

    <p>Al2(SO4)3 · 14.3H2O</p> Signup and view all the answers

    What happens when 1 mg/l of alum is added to water?

    <p>The water alkalinity decreases by 0.5 mg/l</p> Signup and view all the answers

    Why is lime often added with alum?

    <p>To add alkalinity to water</p> Signup and view all the answers

    What is the preferred coagulant for treating high-quality surface water?

    <p>Aluminum Sulfate</p> Signup and view all the answers

    What is the purpose of adding lime to Ferrous Sulfate?

    <p>To raise the pH of water and precipitate ferrous ions</p> Signup and view all the answers

    What is a characteristic of using lime with Ferrous Sulfate?

    <p>It results in non-corrosive water with some hardness</p> Signup and view all the answers

    What is the reaction between HOCI and NH3?

    <p>H2O + NH2Cl</p> Signup and view all the answers

    What is the definition of Free Available Residual Chlorine (FRC)?

    <p>Residual chlorine in water as HOCl or OCl</p> Signup and view all the answers

    What is the point at which all ammonia has been reacted called?

    <p>Point C</p> Signup and view all the answers

    What is the purpose of a vacuum regulator in gas chlorination?

    <p>To generate a vacuum</p> Signup and view all the answers

    Why is nonmetallic piping used for chlorine gas?

    <p>Because it is more resistant to chlorine's corrosive properties</p> Signup and view all the answers

    What is the effect of chlorine gas on human health at high concentrations?

    <p>It causes all of the above</p> Signup and view all the answers

    What is the purpose of chlorine demand?

    <p>To measure the amount of chlorine required to react with reducing agents</p> Signup and view all the answers

    What is the application of chlorine dioxide limited to?

    <p>Taste and odor control</p> Signup and view all the answers

    What is the primary purpose of the two-stage excess lime treatment system shown in Figure 11.7?

    <p>Removal of Ca2+ and Mg2+ from the water</p> Signup and view all the answers

    What is the role of the cation resin in the cation exchange softening process?

    <p>To replace calcium and magnesium ions with sodium ions</p> Signup and view all the answers

    What is the purpose of backwashing the resin in the cation exchange softening process?

    <p>To restore the original condition of the resin</p> Signup and view all the answers

    What is the typical flow rate of a cation exchange softening system?

    <p>6-8 gpm/ft2 surface area</p> Signup and view all the answers

    How much salt is needed to regenerate 1 ft3 of resin and remove approximately 4 Ib of hardness?

    <p>8.5 Ib of salt</p> Signup and view all the answers

    What is the reduction of hardness in a cation exchange softening system dependent on?

    <p>Amount of hardness in raw water and amount of salt to regenerate the bed</p> Signup and view all the answers

    What type of control is typically used in a cation exchange softening system?

    <p>Either manual or automatic control</p> Signup and view all the answers

    What is the purpose of soda ash in the two-stage excess lime treatment system?

    <p>Not mentioned in the content</p> Signup and view all the answers

    What is the byproduct of ozone decomposition in water?

    <p>Hydroxyl free radicals</p> Signup and view all the answers

    What is the purpose of the ozone destructor in an ozonation system?

    <p>To destroy excess ozone</p> Signup and view all the answers

    What is the advantage of ozone over chlorine as a disinfectant?

    <p>Ozone is a stronger oxidizing gas</p> Signup and view all the answers

    What is the pH range for the formation of chlorine dioxide?

    <p>pH 3.5 (minimum residual of Cl2 and Na2ClO)</p> Signup and view all the answers

    What is the disadvantage of using chlorine dioxide as a disinfectant?

    <p>It forms a residual in the distribution system (toxins)</p> Signup and view all the answers

    What is the purpose of flash distillation?

    <p>To remove dissolved salts from water</p> Signup and view all the answers

    What is the most common application of Reverse Osmosis (RO)?

    <p>Purification of brackish water</p> Signup and view all the answers

    What is the direction of water flow in Direct Osmosis?

    <p>From lower salt concentration to higher salt concentration</p> Signup and view all the answers

    Study Notes

    Reverse Osmosis (RO)

    • RO is used to equalize salt content by blocking salt ions and allowing water passage.
    • Osmotic pressure of salt solution (Pos) is the pressure applied to the side of higher salt content to prevent water flow.
    • RO uses high pressure (ΔP) to increase water permeability (Q α (Papplied – Pos)).
    • Papplied is 80-120 psi for demostic use and 350-150 psi for industrial use.
    • Water product is 70-90 % of feed (brackish) and 30% of feed (sea).
    • Membrane materials are:
      • Cellulose acetate (high Q/A in spiral-wound flat sheets)
      • Aromatic polyamide (lower Q/A in hollow fibers to increase A ~ 15 spiral wound membrane)
    • Water product (permeate) and brine (reject) are the outputs of the RO process.

    Scaling Potential

    • Scaling potential is determined by the concentration of ions in the brine (calcium sulfate, calcium carbonate, and silicon dioxide).
    • Example: Ca2+ 200 mg/l in feed, 25% recovery water product with 7 mg/l and reject 779 mg/l (4 times).

    Chemical Treatment Processes

    Definitions:

    • Atomic weight: weight of an element relative to C-12
    • Valence: combining power of an element relative to that of hydrogen atoms of 1 (H+)
    • Flocculation: coagulation reduces the net electrical repulsive forces at particle surfaces using coagulant chemicals
    • Coagulants:
      • Aluminum sulfate for removal of organic matter
      • Iron salt for removal of color, taste, and odor
      • Polymer coagulant used as aids

    Aluminum Sulfate (Filter Alum)

    • Formula: Al2(SO4)3 · 14.3 H2O
    • Available as a powder or liquid alum syrup
    • Every 1 mg/l of alum decreases water alkalinity by 0.5 mg/l (as CaCO3) and increases CO2 by 0.44 mg/l (corrosive and undesired)

    Ferrous Sulfate (Copperas)

    • Formula: FeSO4
    • Green crystal for dry feeding
    • Lime is usually added to raise pH to precipitate ferrous ions as ferric hydroxide by caustic alkalinity

    Ion Exchange Softening

    • Removes Ca2+ and Mg2+ (hardness) by replacing them with sodium using a cation resin (R)

    Cation Exchange Softening Process

    • Ca2+ and Mg2+ are removed from the resin using a backwash solution of sodium chloride
    • The resin is restored to its original condition

    Chlorination

    • HOCl + NH3 → H2O + NH2Cl
    • Free available residual chlorine (FRC) = residual chlorine in water as HOCl or OCl
    • Combined available residual chlorine (CRC) = residual chlorine in water as chlorine or with organic N compounds
    • Chlorine demand (CD) = Chlorine added - (FRC + CRC)

    Chlorine Residual Curve

    • Chlorine reacts with reducing agents, ammonia, and other organic compounds
    • Breakpoint chlorination is used to determine the minimum amount of chlorine required to achieve a residual

    Ozone

    • A strong oxidizing gas that reacts with most organic and inorganic molecules
    • Ozone decomposes in water: O3 + H2O → O2 + 2OH
    • Ozone is generated on-site since its half-life is ~10-30 minutes
    • Ozonation system components:
      • Air preparation or O2 feed
      • Electrical power supply
      • Ozone generation
      • Ozone contactor
      • Ozone destructor

    Reduction of Dissolved Salts

    • Flash Distillation
    • Reverse Osmosis
    • Electro dialysis
    • Process selection depends on size, source of energy, capital, and cost.

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    Description

    This quiz covers the principles and processes of Reverse Osmosis (RO) membranes in equalizing salt content, including membrane materials, osmotic pressure, and water product percentages.

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