CWS Reverse Osmosis Systems 3

Question 1

Which water quality parameter most significantly accelerates RO membrane fouling by biological growth?

Accepted Answer

Low chlorine residual in feedwater

Answer

Insufficient chlorine residual in the feedwater allows bacteria to colonize and form biofilm on the membrane surface.

Question 2

What is 'concentration polarization' in an RO system?

Accepted Answer

Buildup of rejected solutes at the membrane surface reducing flux

Answer

Concentration polarization occurs when rejected ions accumulate at the membrane surface, locally increasing concentration and reducing driving pressure.

Question 3

A CWS technician measures a permeate TDS of 45 mg/L with a feedwater TDS of 500 mg/L. What is the rejection rate?

Accepted Answer

91%

Answer

Rejection rate = (1 - permeate TDS / feed TDS) × 100 = (1 - 45/500) × 100 = 91%.

Question 4

Which pretreatment is required when feedwater contains more than 0.1 mg/L of free chlorine for TFC membranes?

Accepted Answer

Carbon adsorption

Answer

Activated carbon adsorption must remove free chlorine below 0.1 mg/L before the TFC membrane to prevent oxidative degradation.

Question 5

What is the recommended maximum SDI (Silt Density Index) value for feedwater entering most RO systems?

Accepted Answer

SDI < 5

Answer

An SDI of less than 5 is generally required to protect RO membranes from excessive particulate fouling.

(CWS) Certified Water Specialist Practice Test

(CWS) Certified Water Specialist Practice Test

CWS Reverse Osmosis Systems 3