Illinois Class 4 Wastewater Operator Study
Guide | Certification Practice Questions &
Exam Prep
2026/2027
, facultative lagoon A type of wastewater treatment system that uses both aerobic and anaerobic
processes.
detention time The time wastewater spends in a treatment facility, calculated as volume divided by
flow rate.
0.5 MGD A flow rate equivalent to 0.5 million gallons per day.
chlorination The process of adding chlorine to wastewater to kill pathogens.
dechlorinate The process of removing chlorine from wastewater effluent.
minimum oxygen level for confined space 19.5% is considered the safe minimum oxygen level for entry.
safety equipment for confined space A tripod and harness must always be used when entering a confined space.
Illinois EPA The agency that administers wastewater operator certification in Illinois.
trickling filter A common type of wastewater treatment process used in small communities.
aerobic zone in facultative lagoon The primary purpose is nitrification.
pump delivery rate A pump delivering 450 gallons per minute will deliver 108,000 gallons in 4 hours.
primary purpose of chlorination To kill pathogens in wastewater treatment.
chemical used to dechlorinate Sodium bisulfite is commonly used to dechlorinate wastewater effluent.
lagoon volume A lagoon with a volume of 2 million gallons.
confined space entry Safety protocols require a minimum oxygen level of 19.5%.
Guide | Certification Practice Questions &
Exam Prep
2026/2027
, facultative lagoon A type of wastewater treatment system that uses both aerobic and anaerobic
processes.
detention time The time wastewater spends in a treatment facility, calculated as volume divided by
flow rate.
0.5 MGD A flow rate equivalent to 0.5 million gallons per day.
chlorination The process of adding chlorine to wastewater to kill pathogens.
dechlorinate The process of removing chlorine from wastewater effluent.
minimum oxygen level for confined space 19.5% is considered the safe minimum oxygen level for entry.
safety equipment for confined space A tripod and harness must always be used when entering a confined space.
Illinois EPA The agency that administers wastewater operator certification in Illinois.
trickling filter A common type of wastewater treatment process used in small communities.
aerobic zone in facultative lagoon The primary purpose is nitrification.
pump delivery rate A pump delivering 450 gallons per minute will deliver 108,000 gallons in 4 hours.
primary purpose of chlorination To kill pathogens in wastewater treatment.
chemical used to dechlorinate Sodium bisulfite is commonly used to dechlorinate wastewater effluent.
lagoon volume A lagoon with a volume of 2 million gallons.
confined space entry Safety protocols require a minimum oxygen level of 19.5%.
