Wastewater certification levels
Wastewater Class I — Entry-Level Operator
Entry-level wastewater treatment operator certification (ABC Class I). Covers wastewater characteristics, collection systems, preliminary and primary treatment, activated sludge basics, fixed-film systems, lagoons, disinfection, solids handling, lab and process control, safety, and operator math.
Wastewater Class IIWastewater Class II — Intermediate Operator
Intermediate wastewater treatment operator certification (ABC Class II). Covers activated sludge process control, nitrification and denitrification, nutrient removal, clarifier loading, fixed-film and lagoon systems, disinfection, solids handling and digestion, lab and process control, operator math, safety, and regulations.
Wastewater Class IIIWastewater Class III — Advanced Operator
Advanced wastewater treatment operator certification (ABC Class III). Covers SRT-based process control and optimization, BNR configurations (MLE, A2O, Bardenpho), SBR/MBR/IFAS/MBBR systems, clarifier state-point analysis, advanced disinfection, digester and dewatering optimization, instrumentation and SCADA, advanced operator math, energy, safety, and regulatory programs.
Wastewater Class IVWastewater Class IV — Expert / Large System Operator
Highest-level wastewater treatment operator certification (ABC Class IV). Covers process modeling and optimization, advanced BNR and sidestream treatment, energy recovery and digestion (thermal hydrolysis, co-digestion, CHP), membranes and advanced clarification, instrumentation and automation, advanced operator math, plant management and capital planning, regulatory programs, safety 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
AvailableTreatment plant operator exams, entry level through expert. Math, disinfection, filtration, coagulation, regulations.
Start practicing →Distribution
Coming soonDistribution system operator exams — mains, storage, pressure, cross-connection, water quality in the distribution system.
Get notified →Collections
Coming soonCollection system operator exams — gravity sewers, lift stations, I&I, maintenance, and safety.
Get notified →