CWS Ultraviolet Disinfection Systems 4

Question 1

Under the USEPA Surface Water Treatment Rule, what minimum UV dose (mJ/cm²) achieves 3-log inactivation of Cryptosporidium?

Accepted Answer

40 mJ/cm²

Answer

The USEPA LT2ESWTR specifies that 40 mJ/cm² of validated UV dose achieves 3-log (99.9%) inactivation credit for Cryptosporidium.

Question 2

What is the 'reduction equivalent dose' (RED) concept used in UV reactor validation?

Accepted Answer

The equivalent collimated-beam dose that produces the same log inactivation as the reactor under challenge test conditions

Answer

RED translates reactor performance into a collimated-beam equivalent dose, allowing comparison with bench-scale dose-response data to confirm log-inactivation credit.

Question 3

Which hydraulic condition inside a UV reactor reduces germicidal effectiveness by allowing some water to pass through with minimal UV exposure?

Accepted Answer

Short-circuiting or channeling

Answer

Short-circuiting creates preferential flow paths where portions of the water receive insufficient UV exposure time, reducing the effective dose delivered.

Question 4

What is the primary reason iron and manganese are problematic for UV disinfection systems?

Accepted Answer

They deposit on the quartz sleeve, reducing UV transmission and increasing cleaning frequency

Answer

Oxidized iron and manganese form scale on the quartz sleeve, blocking UV transmission and necessitating frequent chemical or mechanical cleaning to maintain dose delivery.

Question 5

What type of ballast is required for pulsed UV lamp operation in advanced disinfection systems?

Accepted Answer

Electronic high-frequency ballast with pulsed power delivery capability

Answer

Pulsed UV systems require electronic ballasts capable of delivering controlled, high-peak power pulses to the lamp rather than continuous sinusoidal power.

(CWS) Certified Water Specialist Practice Test

(CWS) Certified Water Specialist Practice Test

CWS Ultraviolet Disinfection Systems 4