CWS Reverse Osmosis Systems 2 — Questions and Answers
Question 1: What is the typical recovery rate for a residential RO system?
- 75-85%
- 15-25% (Correct answer)
- 45-55%
- 90-95%
Correct answer: 15-25%
Residential RO systems typically recover only 15-25% of feed water as permeate, wasting 75-85% as reject.
Question 2: Which component in an RO system prevents backflow of treated water into the feed line?
- Flow restrictor
- Check valve (Correct answer)
- Pressure tank bladder
- Post-filter
Correct answer: Check valve
A check valve prevents back-siphonage of permeate back into the feed water supply.
Question 3: What is the primary purpose of the flow restrictor in a residential RO system?
- Increase permeate flow rate
- Maintain backpressure to create reject stream (Correct answer)
- Reduce sediment in permeate
- Regulate storage tank pressure
Correct answer: Maintain backpressure to create reject stream
The flow restrictor maintains sufficient backpressure on the reject side to force water through the membrane and produce a concentrate stream.
Question 4: At what feedwater pressure do most residential RO membranes operate optimally?
- 10-20 psi
- 30-40 psi
- 60-80 psi (Correct answer)
- 100-120 psi
Correct answer: 60-80 psi
Most residential RO membranes are rated for 60-80 psi operating pressure to achieve adequate permeate production.
Question 5: Which type of RO membrane material is most commonly used in point-of-use drinking water systems?
- Cellulose acetate (CA)
- Thin-film composite (TFC) (Correct answer)
- Polysulfone
- Polyamide hollow fiber
Correct answer: Thin-film composite (TFC)
Thin-film composite (TFC) membranes dominate residential POU applications due to superior rejection rates and wider pH tolerance.
Question 6: A customer's RO system is producing water very slowly. What is the MOST likely cause?
- Post-filter clogged
- Storage tank fully pressurized with no room for water (Correct answer)
- Elevated feed water temperature
- Incorrectly installed check valve orientation
Correct answer: Storage tank fully pressurized with no room for water
A storage tank whose bladder has failed or that is pre-charged too high creates backpressure that shuts off permeate flow prematurely.
Question 7: What does the term 'salt rejection rate' mean for an RO membrane?
- Percentage of dissolved solids removed from permeate (Correct answer)
- Volume of brine discharged per day
- Ratio of permeate to reject flow
- Membrane resistance to sodium chloride scaling
Correct answer: Percentage of dissolved solids removed from permeate
Salt rejection rate is the percentage of total dissolved solids (or specific ions) removed from the feedwater, expressed as a percentage.
CWS Reverse Osmosis Systems 2
What is the typical recovery rate for a residential RO system?