OTCO BASIC WASTEWATER OPERATOR
CERTIFICATION EXAM: 200 PRACTICE QUESTIONS
WITH VERIFIED ANSWERS, DETAILED RATIONALES,
COMPREHENSIVE STUDY GUIDE, AND LATEST
2026/2027 UPDATES
SECTION 1: BASIC CONCEPTS & DEFINITIONS
Q1: What is the main purpose of a wastewater
treatment plant?
• A. Provide drinking water
• B. Remove contaminants to protect health and
the environment
• C. Produce fertilizer
• D. Generate energy
☑VERIFIED ANSWER: B
Rationale: Wastewater treatment removes
pollutants from sewage to prevent environmental
pollution and protect public health.
,Q2: What does BOD measure?
• A. Biological Oxygen Demand – oxygen used by
microbes to decompose organic matter
• B. Base Oxygen Density
• C. Biochemical Oxidation Degree
• D. Basic Oxygen Demand
☑VERIFIED ANSWER: A
Rationale: BOD indicates the amount of oxygen
microorganisms need to break down organic
pollutants in wastewater.
Q3: The killing of pathogenic bacteria is called:
• A. Sterilization
• B. Disinfection
• C. Coagulation
• D. Oxidation
,☑VERIFIED ANSWER: B
Rationale: Disinfection is the process of killing
pathogenic bacteria. Chlorination and UV are
common disinfection methods.
Q4: What is TSS?
• A. Total Suspended Solids – particles suspended
in water
• B. Total Salt Solution
• C. Total Sulfate Standard
• D. Total Soluble Substances
☑VERIFIED ANSWER: A
Rationale: TSS measures the concentration of solids
that are not dissolved in water and can be removed
by filtration.
Q5: What does DO stand for?
• A. Daily Output
, • B. Dissolved Oxygen
• C. Direct Oxidation
• D. Density Offset
☑VERIFIED ANSWER: B
Rationale: Dissolved oxygen is essential for aerobic
microbial activity in biological treatment processes.
SECTION 2: TREATMENT PROCESSES
Q6: Which process is used first in most wastewater
plants?
• A. Aeration
• B. Screening
• C. Disinfection
• D. Sludge digestion
☑VERIFIED ANSWER: B
Rationale: Screening removes large debris to
CERTIFICATION EXAM: 200 PRACTICE QUESTIONS
WITH VERIFIED ANSWERS, DETAILED RATIONALES,
COMPREHENSIVE STUDY GUIDE, AND LATEST
2026/2027 UPDATES
SECTION 1: BASIC CONCEPTS & DEFINITIONS
Q1: What is the main purpose of a wastewater
treatment plant?
• A. Provide drinking water
• B. Remove contaminants to protect health and
the environment
• C. Produce fertilizer
• D. Generate energy
☑VERIFIED ANSWER: B
Rationale: Wastewater treatment removes
pollutants from sewage to prevent environmental
pollution and protect public health.
,Q2: What does BOD measure?
• A. Biological Oxygen Demand – oxygen used by
microbes to decompose organic matter
• B. Base Oxygen Density
• C. Biochemical Oxidation Degree
• D. Basic Oxygen Demand
☑VERIFIED ANSWER: A
Rationale: BOD indicates the amount of oxygen
microorganisms need to break down organic
pollutants in wastewater.
Q3: The killing of pathogenic bacteria is called:
• A. Sterilization
• B. Disinfection
• C. Coagulation
• D. Oxidation
,☑VERIFIED ANSWER: B
Rationale: Disinfection is the process of killing
pathogenic bacteria. Chlorination and UV are
common disinfection methods.
Q4: What is TSS?
• A. Total Suspended Solids – particles suspended
in water
• B. Total Salt Solution
• C. Total Sulfate Standard
• D. Total Soluble Substances
☑VERIFIED ANSWER: A
Rationale: TSS measures the concentration of solids
that are not dissolved in water and can be removed
by filtration.
Q5: What does DO stand for?
• A. Daily Output
, • B. Dissolved Oxygen
• C. Direct Oxidation
• D. Density Offset
☑VERIFIED ANSWER: B
Rationale: Dissolved oxygen is essential for aerobic
microbial activity in biological treatment processes.
SECTION 2: TREATMENT PROCESSES
Q6: Which process is used first in most wastewater
plants?
• A. Aeration
• B. Screening
• C. Disinfection
• D. Sludge digestion
☑VERIFIED ANSWER: B
Rationale: Screening removes large debris to
