How to study
- Get the need-to-know list. Your state certification program publishes what each grade covers. Study to that list, not to a textbook's table of contents.
- Do the math every day. Math is where most candidates lose points. Work ten problems a day for a month. Write the units on every line; units catch most mistakes.
- Know the core formulas cold. Pounds, detention time, SRT, F/M, SVI, SOR, SLR, WOR, chemical feed and pump horsepower. Many states provide a formula sheet; practice with the one you will get. Our printable formula sheet covers the same ground.
- Tie theory to your plant. When you read about nitrification, look at your own ammonia, alkalinity and DO data. Questions are easier when you have seen the answer at work.
- Take timed practice tests. Learn your pace. Skip a hard problem, mark it and come back.
- Read every answer. On exam day, look for "most likely", "first" and "except". Eliminate the two clearly wrong answers first.
Topics that show up on almost every exam
- Activated sludge control: SRT, F/M, MLSS, SVI, RAS and WAS (basics, RAS and WAS)
- Nitrification, denitrification and alkalinity (nitrification)
- Clarifier loading rates (clarifiers)
- Disinfection, chlorine demand and dechlorination (disinfection)
- Solids handling and digesters (solids handling)
- Safety: confined spaces, lockout and tagout, hydrogen sulfide, chlorine
- Lab: BOD, TSS, settleometer, DO, pH, sampling and holding times
- Pumps, hydraulics and unit conversions
Sample math with answers
These use White River WRRF numbers (a fictional plant). Work each one before you open the answer.
A plant treats 7.09 MGD with a primary effluent BOD of 150 mg/L. How many pounds of BOD per day go to aeration?
Show answer
7.09 x 150 x 8.34 = 8,870 lb/d (about 8,900 lb/d).
Aeration volume is 3.6 MG and MLSS is 3,000 mg/L. What is the aeration inventory in pounds?
Show answer
3.6 x 3,000 x 8.34 = 90,072 lb.
Using the inventory above, WAS solids are 7,206 lb/d and effluent solids are 534 lb/d. What is the SRT?
Show answer
90,072 / (7,206 + 534) = 90,072 / 7,740 = 11.6 days.
A settleometer reads 350 mL/L after 30 minutes with MLSS of 3,000 mg/L. What is the SVI?
Show answer
350 x 1,000 / 3,000 = 117 mL/g.
Influent flow is 8.0 MGD and the 30 minute settled volume is 350 mL/L. Estimate RAS flow.
Show answer
RAS = 8.0 x 350 / (1,000 - 350) = 2,800 / 650 = 4.3 MGD.
Four 90 ft clarifiers treat 8.0 MGD. What is the surface overflow rate?
Show answer
Area = 0.785 x 90 x 90 x 4 = 25,434 ft² (25,447 with pi). SOR = 8,000,000 / 25,447 = 314 gpd/ft².
The same clarifiers receive 8.0 MGD plus 4.0 MGD RAS at 3,000 mg/L MLSS. What is the solids loading rate?
Show answer
(8.0 + 4.0) x 3,000 x 8.34 / 25,447 = 300,240 / 25,447 = 11.8 lb/d/ft².
How much alkalinity is needed to nitrify 30 mg/L of ammonia nitrogen, with no denitrification, keeping 50 mg/L residual?
Show answer
30 x 7.14 + 50 = 264 mg/L as CaCO3.
A pump delivers 700 gpm against 60 ft TDH. Pump efficiency is 75%. What brake horsepower is needed?
Show answer
WHP = 700 x 60 / 3,960 = 10.6 hp. BHP = 10.6 / 0.75 = 14.1 hp.
A chlorine contact tank is dosed at 8 mg/L and the residual is 1.5 mg/L. What is the demand?
Show answer
8 - 1.5 = 6.5 mg/L.
Wastewater Academy prep classes
Brad Musick's self-paced classes at Wastewater Academy go deeper on exam topics:
- Indiana Class I and II Certification: Covers the Indiana Class I and II exams.
- Indiana Class III and IV Certification: Covers the Indiana Class III and IV exams, with heavy math practice.
- Indiana Industrial Class C and D: For Indiana industrial Class C and D operators.
- free practice quizzes: Free practice quizzes.