Wastewater certification levels
Wastewater Treatment Class 1 — Entry-Level Operator
Entry-level practice for the ABC Class I wastewater treatment exam — wastewater characteristics, preliminary/primary treatment, activated sludge and fixed-film basics, lagoons, disinfection, solids handling, and operator math.
Wastewater Class 2Wastewater Treatment Class 2 — Intermediate Operator
Intermediate practice for the ABC Class II wastewater exam — activated-sludge process control, nitrification/denitrification, clarifier loading, fixed-film and lagoon systems, disinfection, digestion, and operator math.
Wastewater Class 3Wastewater Treatment Class 3 — Advanced Operator
Advanced practice for the ABC Class III wastewater exam — SRT-based process control, BNR configurations (MLE, A²O, Bardenpho), SBR/MBR/IFAS systems, state-point analysis, digester optimization, SCADA, and advanced math.
Wastewater Class 4Wastewater Treatment Class 4 — Expert / Large System Operator
Top-level practice for the ABC Class IV wastewater exam — process modeling and optimization, advanced BNR and sidestream treatment, energy recovery and digestion, membranes, automation, plant management, and complex troubleshooting.
Practice by topic
Activated Sludge & Process Control
F/M, MCRT, SVI, RAS/WAS, DO control, and reading the secondary clarifier.
TopicWastewater Characteristics & Sampling
BOD, COD, TSS, flow, and how to take a compliant wastewater sample.
TopicWastewater Disinfection
Chlorine, UV, dechlorination, dose vs demand, and contact time.
TopicFixed-Film & Lagoon Systems
Trickling filters, RBCs, and stabilization ponds and lagoons.
TopicBiological Nutrient Removal
Nitrification, denitrification, and biological phosphorus removal.
TopicWastewater Operator Math
The pounds formula, loading rates, detention time, and process-control math.
TopicPreliminary & Primary Treatment
Bar screens, grit removal, primary clarifiers, and removal efficiency.
TopicSecondary Clarification
Surface overflow and solids loading rates, weirs, and settling problems.
TopicSolids Handling & Digestion
Thickening, digestion, dewatering, and biosolids.
Find your state's requirements
Class names and exam rules vary by state. See how these tests map to your state's wastewater operator classes on the state pages.
Related study guides
Other certifications
We cover every water-industry operator certification — pick the one you're studying for.
Drinking Water
Treatment plant operator exams, entry level through expert. Math, disinfection, filtration, coagulation, regulations.
Start practicing →Distribution
Distribution system operator exams — mains, storage, pressure, cross-connection, water quality in the distribution system.
Start practicing →Collections
Collection system operator exams — gravity sewers, lift stations, I&I, maintenance, and safety.
Start practicing →