WTO Disinfection Processes 2

Question 1

What is the primary advantage of using chloramines over free chlorine for disinfection?

Accepted Answer

Chloramines produce fewer disinfection byproducts

Answer

Chloramines form fewer trihalomethanes and haloacetic acids compared to free chlorine, making them preferred in systems with high organic precursors.

Question 2

Which parameter most directly affects the disinfection efficiency of chlorine in water treatment?

Accepted Answer

pH

Answer

pH determines the ratio of hypochlorous acid (HOCl) to hypochlorite ion (OCl⁻); HOCl is the more effective disinfectant and dominates at lower pH.

Question 3

A water system switches from free chlorine to chloramine disinfection. What operational concern must be addressed?

Accepted Answer

Nitrification in the distribution system

Answer

Chloramine systems are susceptible to nitrification, where ammonia-oxidizing bacteria convert ammonia to nitrite, depleting the disinfectant residual.

Question 4

What does CT value represent in disinfection calculations?

Accepted Answer

Chlorine concentration multiplied by contact time

Answer

CT is the product of disinfectant concentration (C, in mg/L) and contact time (T, in minutes), used to evaluate pathogen inactivation credit.

Question 5

Why is ultraviolet (UV) disinfection considered ineffective against Cryptosporidium in terms of CT-based comparison?

Accepted Answer

CT tables do not apply to UV; UV efficacy is measured in mJ/cm²

Answer

UV disinfection efficacy is measured by UV dose (mJ/cm²), not CT; Cryptosporidium is actually highly susceptible to UV at standard doses.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO Disinfection Processes 2