semplr.

Exams · Certifications · Licensing

Water & Wastewater Operator (WPI/ABC Class I) — Practice Exam

WT treatment: disinfection: practice questions

Our Water/Wastewater Operator bank has 15 questions on this topic. Here are 5 of them with answers; the full mock exam draws from every topic, like the real one.

Start the free mock exam

Question 1 · Water Treatment Class I

What is breakpoint chlorination?

  1. Stopping chlorination when the pump fails
  2. Stopping the chlorine feed whenever the feed pump fails or the gas cylinder runs empty
  3. Stopping chlorination when the feed pump fails or the cylinder runs empty
  4. Adding chlorine until ammonia and other demand are satisfied and free residual begins to form
Show the answer

D. Adding chlorine until ammonia and other demand are satisfied and free residual begins to form — Past the breakpoint, free chlorine residual rises with dose.

Question 2 · Water Treatment Class I

What is the MCL for total trihalomethanes (TTHM)?

  1. 0.010 mg/L
  2. 0.060 mg/L
  3. 0.080 mg/L
  4. 1.0 mg/L
Show the answer

C. 0.080 mg/L — 40 CFR 141.64; HAA5 is 0.060 mg/L.

Question 3 · Water Treatment Class I

What is the maximum residual disinfectant level (MRDL) for chlorine?

  1. 0.2 mg/L
  2. 0.8 mg/L
  3. 0.8 mg/L, the same as chlorine dioxide
  4. 4.0 mg/L as Cl2
Show the answer

D. 4.0 mg/L as Cl2 — 40 CFR 141.65; chlorine dioxide's MRDL is 0.8 mg/L.

Question 4 · Water Treatment Class I

The chlorine dose is 3.0 mg/L and the residual is 0.8 mg/L. What is the chlorine demand?

  1. 0.8 mg/L
  2. 2.2 mg/L
  3. 2.4 mg/L
  4. 3.8 mg/L
Show the answer

B. 2.2 mg/L — Demand = dose − residual.

Question 5 · Water Treatment Class I

What forms when chlorine reacts with ammonia?

  1. Ozone
  2. Chlorine dioxide
  3. Chloramines
  4. Trihalomethanes
Show the answer

C. Chloramines — Chloramines are a longer-lasting but weaker disinfectant.

More Water/Wastewater Operator topics