Class B Wastewater Treatment Plant Operator Exam

When collecting a sample for dissolved oxygen measurement, which technique is most important for avoiding a biased result?

Filter the sample before measuring dissolved oxygen

Hold the sample on ice until the end of shift

Mix vigorously before measuring the dissolved oxygen

Minimize aeration and analyze or fix the sample promptly

Report this question (opens in a new tab)

A permitted wastewater facility diverts reclaimed water to a reuse system. The effluent suddenly fails the treatment quality required for that reuse application. What is the best operator response?

Divert off-spec water to the approved contingency pathway

Continue reuse temporarily while increasing the disinfectant dose

Blend off-spec water with compliant reclaimed water

Reduce reuse flow but continue delivering the water

Report this question (opens in a new tab)

A trickling filter has poor wetting across part of the media because several distributor nozzles are plugged. What is the most likely treatment effect?

Secondary clarification will replace the lost biological treatment

Uneven loading will reduce effective media use and treatment

Lower local loading will improve removal on the dry media

Extra ventilation will compensate for lost wastewater distribution

Report this question (opens in a new tab)

A plant uses an anoxic zone followed by an aerobic zone. What is the primary nitrogen-removal purpose of the anoxic zone?

Biologically reduce nitrate to nitrogen gas

Oxidize ammonia to nitrate before the aerobic zone

Release phosphorus from biomass for clarifier removal

Oxidize residual BOD with dissolved oxygen in the zone

Report this question (opens in a new tab)

An anaerobic digester is receiving the same sludge feed as usual, but mixing performance has deteriorated and a thick scum layer is developing. What is the most appropriate operator response?

Restore effective mixing and evaluate the cause of scum accumulation

Reduce digester temperature to slow gas production

Increase raw-sludge feed to dilute the scum layer

Increase sludge withdrawal until the scum layer drops

Report this question (opens in a new tab)

Effluent ammonia rises after the plant sharply decreases solids retention time to control MLSS. Dissolved oxygen remains adequate. What is the most likely process effect?

Lower SRT is increasing the nitrifier growth rate

Denitrifiers are washing out while nitrifiers remain stable

Nitrifiers are washing out because SRT is too low

Primary clarification is removing less ammonia from influent

Report this question (opens in a new tab)

A primary clarifier develops persistent floating scum and septic odor after sludge pumping was reduced for several days. What is the most likely cause?

Hydraulic overloading is causing freshly settled sludge to float and carry over

Excess sludge withdrawal is pulling gas into the hopper

Primary sludge is being retained too long and becoming septic

Low wastewater temperature is increasing gas production

Report this question (opens in a new tab)

In an enhanced biological phosphorus-removal process, why is protecting the anaerobic zone from nitrate important?

Nitrate is improving anaerobic phosphorus release by PAOs

Nitrate is chemically precipitating phosphate in the zone

Nitrate is increasing fermentation of readily biodegradable carbon

Nitrate is consuming carbon needed for biological phosphorus removal

Report this question (opens in a new tab)

A belt filter press processes sludge at 80 gpm for 6 hours. Approximately how many gallons of sludge are processed?

48,000 gallons

288,000 gallons

28,800 gallons

4,800 gallons

Report this question (opens in a new tab)

An aeration basin DO is very low near the outlet during peak loading, and effluent BOD is increasing. Blower capacity is available. What is the best immediate process-control response?

Reduce aeration to promote anoxic metabolism near the outlet

Increase aeration in the oxygen-deficient zone

Increase wasting before restoring available aeration capacity

Increase RAS flow while leaving oxygen transfer unchanged

Report this question (opens in a new tab)

A reclaimed-water storage pond is receiving more flow than the reuse system can accept, and available storage is nearly exhausted. Which response is most appropriate?

Use the permitted contingency before storage capacity is exceeded

Increase reuse-system pressure within normal limits to stimulate customer demand

Hold additional water in treatment units until demand returns

Reduce reuse treatment while upstream flow remains unchanged

Report this question (opens in a new tab)

A worker must enter a permit-required confined space at a wastewater facility. Atmospheric testing shows an unsafe condition. What should occur before entry?

Allow entry with an attendant and air-purifying respirator

Control the hazard and retest until entry conditions are acceptable

Enter briefly before ventilation to confirm the initial reading

Reclassify the space after documenting the unsafe atmosphere

Report this question (opens in a new tab)

A conventional activated-sludge plant develops filamentous bulking: SVI rises, sludge settles slowly, and effluent TSS increases. Which response is most appropriate first?

Increase wasting immediately to lower MLSS

Increase RAS until the clarifier blanket falls

Reduce aeration throughout the basin to protect floc

Diagnose the process condition causing filamentous growth

Report this question (opens in a new tab)

A plant experiences repeated secondary-clarifier solids washout during short peak-flow events, while normal-flow settling tests are acceptable. Which long-term action best addresses the pattern?

Use coagulant addition as the primary hydraulic control

Increase RAS during every peak regardless of blanket depth

Evaluate peak hydraulic loading and flow-equalization options

Increase MLSS so more solids remain during peak flow

Report this question (opens in a new tab)

A sludge pump is stopped at its local control station for maintenance, but electrical energy is still available to the motor. What additional control is required before hands-on work begins?

Guard the local OFF switch while maintenance proceeds

Isolate hazardous energy and apply lockout/tagout

Close the discharge valve while electrical power remains available

Trip the motor starter and attach a maintenance tag

Report this question (opens in a new tab)

Two parallel primary clarifiers receive unequal flow because one inlet gate is partly closed. Why is this operationally important?

The overloaded clarifier may have poorer solids removal

The underloaded clarifier will have poorer solids settling

Each clarifier will receive a different influent concentration

The overloaded clarifier will have a lower overflow rate

Report this question (opens in a new tab)

A surface-water discharge is approaching a permit limit during a period of low receiving-water flow. Which information is most important for the operator when deciding whether process changes are needed?

Compare receiving-water flow with its seasonal historical operating range

Compare influent loading with the plant design flow

Compare the result only with last month's average

Compare current effluent results and trends with permit limits

Report this question (opens in a new tab)

A plant using chlorine disinfection must reduce chlorine residual before discharge. Which operating change directly increases dechlorination capacity when sulfur-based dechlorination is used?

Increase chlorine feed ahead of the contact chamber

Reduce dechlorinating dose to limit sulfite residual

Increase chlorine contact time before the downstream dechlorination point

Increase dechlorinating dose to match chlorine load and flow

Report this question (opens in a new tab)

A plant's influent BOD remains stable, but effluent BOD increases while effluent TSS also increases. Which interpretation is most reasonable?

Loss of nitrification is raising both BOD and TSS

Higher soluble influent BOD is driving the increase

Improved primary removal is increasing secondary-effluent BOD

Solids carryover is contributing to the higher effluent BOD

Report this question (opens in a new tab)

A digester contains 600,000 gallons of sludge and receives 30,000 gallons of sludge per day. Ignoring withdrawals other than the equivalent daily throughput, what is the nominal detention time?

50 days

12 days

20 days

5 days

Report this question (opens in a new tab)

A primary clarifier receives 3.0 MGD and has a surface area of 5,000 ft². What is the approximate surface overflow rate?

6,000 gal/day/ft²

600 gal/day/ft²

167 gal/day/ft²

1,500 gal/day/ft²

Report this question (opens in a new tab)

Plant performance data show a potential permit noncompliance. What is the most appropriate operator action?

Replace the result if a repeat analysis is compliant

Wait for the next routine sample before documenting the result

Follow permit reporting requirements and begin correcting the condition

Wait for the monthly average before taking action

Report this question (opens in a new tab)

An RBC shaft continues turning, but a large portion of the biological media has broken away. What is the main process concern?

Higher recirculation will replace the lost biological surface

Loss of biofilm surface area will reduce treatment capacity

Higher shaft speed will restore capacity on the remaining media

More secondary clarification will replace attached-growth treatment

Report this question (opens in a new tab)

A Florida domestic wastewater facility is operating under a discharge permit. Which document should the operator use as the primary source for the facility-specific effluent limits and monitoring requirements?

The facility's current permit and incorporated conditions

Florida Administrative Code Chapter 62-600 by itself

The approved analytical method for the monitored parameter

Florida's operator-certification handbook and license conditions

Report this question (opens in a new tab)

An ultraviolet disinfection system shows a rising UV dose demand even though lamp output is normal. Effluent turbidity and suspended solids have increased. Which action best addresses the likely cause?

Increase UV intensity to compensate for the higher effluent turbidity

Increase channel velocity through the UV reactor

Reduce final-clarifier detention to limit solids buildup

Restore upstream solids removal to reduce particle shielding

Report this question (opens in a new tab)

A chlorine contact chamber is meeting the target chlorine residual at the outlet, but fecal-indicator results have become inconsistent. Plant flow has also increased and a tracer study previously showed significant short-circuiting. What is the most appropriate operational concern to investigate first?

Poor mixing at the chlorine injection point

Reduced effective contact time from hydraulic short-circuiting

Increased chlorine demand from higher secondary-effluent ammonia

Inaccurate flow-paced chlorine feed at peak flow

Report this question (opens in a new tab)

A gravity thickener produces dilute underflow while the supernatant contains excessive solids. Which operating issue should be investigated first?

Insufficient supernatant return to the plant headworks

Excessive feed-solids concentration for downstream dewatering

Excessive underflow withdrawal with inadequate compaction time

Hydraulic or solids overloading of the thickener

Report this question (opens in a new tab)

Strong rotten-egg odor develops in a wastewater wet well after long periods of low flow. What is the most likely underlying condition?

Elevated ammonia is producing the characteristic rotten-egg odor

Turbulence is stripping volatile organics with a sulfide odor

Septic anaerobic conditions are generating hydrogen sulfide

Recent chlorination is releasing a sulfur-containing gas

Report this question (opens in a new tab)

A facility adds ferric salt for chemical phosphorus removal. What operating consequence should be anticipated as the dose is increased?

Lower solids because ferric converts biomass to soluble phosphorus

More chemical sludge and a higher solids-handling load

Less sludge because phosphorus remains dissolved in effluent

No sludge change because ferric salts act catalytically

Report this question (opens in a new tab)

Why is thickening waste sludge before digestion often operationally beneficial?

It converts dissolved solids into settleable solids

It reduces the volume handled by downstream solids processes

It increases volatile-solids destruction before digestion

It provides the required final pathogen reduction

Report this question (opens in a new tab)

A force main repeatedly arrives at the treatment plant with septic wastewater and high sulfide. Which strategy best addresses odor formation at its source?

Reduce septic detention or apply a source-control treatment

Increase odor scrubbing only at the treatment plant

Increase aeration only after wastewater reaches the headworks

Increase secondary solids inventory to absorb incoming sulfide

Report this question (opens in a new tab)

An activated-carbon odor-control unit receives a stable hydrogen-sulfide inlet load, but outlet odor and measured H2S are steadily increasing while airflow remains normal. What should the operator investigate first?

Carbon-media exhaustion or channeling through the bed

Shorter wet-well detention and lower upstream sulfide formation

Higher return-sludge flow reducing odor-control fan capacity

Low final-disinfection UV dose allowing sulfide breakthrough

Report this question (opens in a new tab)

An activated-sludge secondary clarifier develops rising sludge several hours after solids settle normally. Nitrate is present in the return sludge. What is the most likely mechanism?

Excess aeration is trapping air within the settled floc

Filamentous bulking is preventing normal initial settling

Hydraulic overloading is washing sludge over the weirs

Denitrification is generating gas that lifts settled sludge

Report this question (opens in a new tab)

A chlorination system maintains the same chlorine feed rate while ammonia in the secondary effluent rises sharply. What result should the operator expect if no other condition changes?

Higher residual because ammonia promotes breakpoint conditions

Higher chlorine demand and a lower measurable residual

Lower chlorine demand and a higher free residual

Little residual change because feed rate is unchanged

Report this question (opens in a new tab)

Primary clarifier effluent TSS increases while influent flow and influent TSS remain stable. The sludge blanket is much higher than normal. What is the best first process adjustment?

Increase sludge withdrawal to lower the blanket

Decrease sludge pumping to allow more blanket compaction

Increase primary-effluent recycle to improve solids contact

Rebalance influent flow away from the affected clarifier

Report this question (opens in a new tab)

A plant treats 2.4 MGD with an influent BOD of 220 mg/L. Approximately how many pounds of BOD enter the plant each day?

8,800 lb/day

12,700 lb/day

4,400 lb/day

1,830 lb/day

Report this question (opens in a new tab)

Mixed-liquor dissolved oxygen is consistently high, ammonia is near zero, and nitrate in the aeration effluent is high. What does this combination indicate?

Primary clarification is causing the high nitrate result

Nitrification is occurring, but denitrification may be limited

Nitrification is failing even though ammonia has fallen to near zero

Low aeration-basin DO is preventing ammonia oxidation

Report this question (opens in a new tab)

A belt filter press cake suddenly becomes wetter after polymer feed is lost, while sludge feed characteristics remain stable. What is the most appropriate response?

Increase washwater pressure on the unconditioned sludge

Increase belt speed to shorten the drainage period

Restore and optimize polymer conditioning

Reduce sludge feed while leaving polymer out of service

Report this question (opens in a new tab)

A chlorine leak alarm activates in a chemical room. An operator who is not part of a trained hazardous-material entry team is nearby. What is the appropriate immediate action?

Enter briefly to close the nearest manual chlorine valve

Ventilate first and enter when chlorine odor decreases

Use a cartridge respirator to inspect from the doorway

Keep clear and initiate the facility emergency response procedure

Report this question (opens in a new tab)

Return activated sludge concentration falls and the secondary clarifier blanket rises despite stable influent flow. What operating condition should be checked first?

Reduce aeration-basin DO to improve floc density

Increase hydraulic loading to push solids toward the hopper

Increase WAS first to reduce the clarifier solids inventory

Check RAS pumping, return rate, and clarifier solids withdrawal

Report this question (opens in a new tab)

A laboratory balance used for total-solids work shows an unacceptable check-weight result before samples are weighed. What should the analyst do?

Increase sample drying time to compensate for the error

Apply a correction factor based on the check-weight error

Average duplicate weights to offset the balance bias

Stop using that balance for reportable work until QC passes

Report this question (opens in a new tab)

An activated-sludge plant has the following trend: effluent ammonia is rising, dissolved oxygen is adequate, and mixed-liquor temperature has dropped substantially. What does this pattern most strongly suggest?

Reduced nitrification capacity caused by colder conditions

Carbon limitation in the plant's anoxic treatment zone

Acute toxic inhibition unrelated to the temperature change

Loss of heterotrophs from excessive sludge wasting

Report this question (opens in a new tab)

A centrifuge feed sludge normally measures 3.0% total solids. A new result is 0.8%, and cake production drops sharply with no equipment change. What should the operator conclude first?

The feed sludge is much more dilute than normal

Improved capture is lowering the measured feed solids

Higher digestion efficiency is reducing feed solids concentration

Polymer overfeed is diluting the centrifuge feed sludge

Report this question (opens in a new tab)

Why should a well-mixed wastewater sample be subsampled promptly for suspended-solids analysis?

Let the sample settle before withdrawing a stable aliquot

Mix well and subsample promptly to keep the aliquot representative

Decant supernatant before mixing to reduce coarse-solids bias

Filter the full sample before selecting the analysis portion

Report this question (opens in a new tab)

An aeration basin has a volume of 1.2 MG and an MLSS concentration of 2,500 mg/L. Approximately how many pounds of mixed-liquor suspended solids are in the basin?

3,000 lb

62,500 lb

25,000 lb

10,000 lb

Report this question (opens in a new tab)

During a BOD5 test, the undiluted sample and the lowest dilution both have less than the required dissolved oxygen remaining after incubation. What should the analyst do on the repeat test?

Add more seed so the final DO remains acceptable

Increase incubation temperature to stabilize the final DO

Shorten incubation and convert the result to five-day BOD

Prepare higher dilutions so a bottle meets valid DO criteria

Report this question (opens in a new tab)

A settleability test shows a rapidly settling sludge that forms a compact blanket, while the secondary clarifier effluent remains clear. What is the best interpretation?

Rising sludge caused by denitrification in the blanket

Early filamentous bulking that has not yet affected effluent clarity

Good sludge settleability and effective clarifier separation

Pin floc caused by weak biological floc formation

Report this question (opens in a new tab)

A Florida operator needs to verify the minimum staffing requirements that apply to a domestic wastewater treatment facility's classification and operating schedule. Which source is most directly relevant?

Florida Administrative Code Chapter 62-610

Florida Administrative Code Chapter 62-699

Florida Administrative Code Chapter 62-602

Florida Administrative Code Chapter 62-640

Report this question (opens in a new tab)

A biological nutrient-removal plant has good nitrification but poor denitrification. Nitrate entering the anoxic zone is adequate, but readily biodegradable carbon is very low. What adjustment is most directly related to the limitation?

Increase dissolved oxygen in the anoxic zone

Increase solids wasting from the aerobic treatment zone

Increase the available carbon source for denitrification

Reduce the internal nitrate recycle despite adequate nitrate

Report this question (opens in a new tab)

An anaerobic digester shows falling gas production, rising volatile acids, and decreasing pH. What condition is most likely developing?

Anaerobic digester instability from accumulating volatile acids

Improved methane formation with faster acid destruction

A gas-meter problem is causing low indicated gas while digestion chemistry remains stable

Organic underloading with excessive alkalinity consumption

Report this question (opens in a new tab)