Reverse Osmosis Systems Flashcards
7 cards from real CWS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Reverse Osmosis Systems flashcards as text
Which water quality parameter most significantly accelerates RO membrane fouling by biological growth?
Answer: Low chlorine residual in feedwater
Insufficient chlorine residual in the feedwater allows bacteria to colonize and form biofilm on the membrane surface.
What is 'concentration polarization' in an RO system?
Answer: Buildup of rejected solutes at the membrane surface reducing flux
Concentration polarization occurs when rejected ions accumulate at the membrane surface, locally increasing concentration and reducing driving pressure.
A CWS technician measures a permeate TDS of 45 mg/L with a feedwater TDS of 500 mg/L. What is the rejection rate?
Answer: 91%
Rejection rate = (1 - permeate TDS / feed TDS) × 100 = (1 - 45/500) × 100 = 91%.
Which pretreatment is required when feedwater contains more than 0.1 mg/L of free chlorine for TFC membranes?
Answer: Carbon adsorption
Activated carbon adsorption must remove free chlorine below 0.1 mg/L before the TFC membrane to prevent oxidative degradation.
What is the recommended maximum SDI (Silt Density Index) value for feedwater entering most RO systems?
Answer: SDI < 5
An SDI of less than 5 is generally required to protect RO membranes from excessive particulate fouling.
How does increasing feedwater temperature affect RO membrane permeate production?
Answer: Increases flux due to decreased water viscosity
Warmer water is less viscous and diffuses through the membrane more easily, increasing permeate flux approximately 3% per °C.
What is the function of the auto-shutoff valve (ASO) in a residential RO system?
Answer: Closes the drain when tank is full to stop membrane operation
The ASO valve senses storage tank pressure and shuts off feed flow to the membrane when the tank reaches about 2/3 of line pressure.