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Questions and Answers
What is the primary driving force for ion mobility in electrodialysis?
Which of the following is NOT a method of membrane maintenance?
What is the primary objective of backwashing in membrane filtration?
What is the role of air sparging in membrane cleaning?
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What is the primary mechanism of electrodialysis?
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What is the result of not maintaining membrane modules?
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What is the primary goal of chemical cleaning in membrane maintenance?
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What is the primary benefit of using backwashing in membrane filtration?
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What is the primary mechanism of membrane fouling in water treatment?
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What is the frequency range for automatic backwash cycles in low-pressure membrane systems?
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Study Notes
Pretreatment in Membrane Processes
- Pretreatment can modify feed water to prevent membrane plugging, fouling, and scaling, and prolong membrane life.
- Various pretreatments include biofiltration, advanced oxidation, pH adjustment, chlorination, and activated carbon.
Household Purification of Water
- Boiling: kills bacteria, spores, cysts, and ova, yielding sterilized water; removes temporary hardness; alters taste but is harmless.
- Chemical disinfection:
- Bleaching powder: contains 33% available chlorine; unstable on exposure to air, light, and moisture.
- Chlorine solution: prepared from bleaching powder; loses chlorine on exposure to light or prolonged storage.
- High-test hypochlorite: more stable than bleaching powder; contains 60-70% available chlorine.
- Chlorine tablets: suitable for small quantities of water but costly.
- Iodine: used for emergency disinfection of water; high costs and physiological activity limit its use.
- Potassium permanganate: no longer recommended due to its oxidizing properties and inability to kill all bacteria.
Membrane Cleaning and Maintenance
- Air sparging: helps scour material off the membrane surface, reducing particles and fouling.
- Chemical cleaning: targets contaminants causing irreversible fouling; frequency depends on membrane characteristics and source water quality.
- Backwashing: removes surface cake during membrane filtration cycle; targets reversible fouling; frequency ranges from 30-90 minutes.
Membrane Processes
- Electrodialysis: flow of ions via an ion exchange membrane, driven by electrical potential; excludes water movement.
- Dialysis: used for desalting, buffer exchange, removal of labeling reagents, drug binding studies, cell growth and feeding, virus purification, and blood treatment.
Importance of Pretreatment in Membrane Processes
- Surface waters require more extensive pretreatment than ground waters due to suspended solids and biological matter.
- Pretreatment coagulation and clarification may be necessary if raw water solids content is high.
- Pretreatment can condition feed water to allow effective membrane treatment.
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Description
This quiz covers various methods of water purification, including pretreatment techniques to prevent membrane fouling and household purification methods such as boiling, chemical disinfection, and filtration.
