Class B Wastewater Treatment Operator Exam

A plant's solids retention time has been steadily increasing. Effluent ammonia remains low, but settleability is worsening and the sludge shows other signs of being too old. Which control change is most appropriate?

Stop wasting to preserve all biomass.

Increase influent BOD by bypassing preliminary treatment.

Increase waste activated sludge rate gradually to reduce solids retention time.

Reduce return activated sludge to zero.

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A rectangular aeration basin is 80 ft long, 40 ft wide, and 12 ft deep. Flow is 0.80 MGD. Using 7.48 gal/ft³, what is the approximate theoretical detention time?

17.2 hours

4.3 hours

8.6 hours

12.0 hours

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An operator repeatedly skips a required plant log entry despite prior coaching. Which supervisory response is most appropriate?

Publicly criticize the operator during shift change to discourage others.

Document the problem, restate the requirement, follow the utility's corrective-action process, and verify improvement.

Change the permit reporting method so the log entry is no longer needed.

Ignore the issue because the operator's process work is otherwise good.

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A primary sludge line plugs repeatedly. Operators find very thick sludge in the hopper because withdrawal intervals have become long. Which change is most appropriate?

Stop withdrawing sludge until the solids become denser.

Withdraw sludge more frequently and verify the sludge line and pump remain clear.

Increase aeration-basin DO to thin the primary sludge.

Increase effluent flow over the clarifier weirs.

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Grit removed from an aerated grit chamber contains excessive putrescible organic material and develops strong odors. Which operating change is most appropriate?

Operate the grit chamber so organics remain suspended while heavier inorganic grit still settles.

Stop grit removal until the organic material decomposes.

Add return activated sludge to the grit chamber.

Reduce wastewater velocity as much as possible so all solids settle.

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A proposed wastewater line must cross near a potable-water line, and the standard separation cannot be maintained. What is the appropriate Class B operator-level response during design review?

Use an allowed protective construction method and materials meeting Chapter 217 criteria.

Flatten the wastewater-pipe slope until the standard separation is no longer required.

Accept the crossing if both pipes are new and pressure-tested before service.

Use a thinner-wall wastewater pipe so the crossing can be installed more easily.

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An aerated lagoon develops widespread septic odors and black water after one of two aerators fails during a period of high organic loading. What is the best response?

Stop all monitoring until the odor disappears.

Restore adequate aeration and evaluate whether loading must be temporarily reduced or redistributed.

Raise the effluent chlorine dose as the only corrective action.

Increase sludge wasting from a secondary clarifier that the lagoon does not have.

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Before an employee enters a permit-required confined space at a wastewater facility, which action is most appropriate?

Test the atmosphere, isolate hazards, and follow the required confined-space procedure.

Enter promptly after opening the cover so accumulated gases can escape naturally.

Begin ventilation only after the entrant reports dizziness or breathing difficulty.

Use odor as the primary test because dangerous gases are usually easy to detect.

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Wastewater entering a chlorine contact basin has a chlorine demand of 8.0 mg/L. The operator wants a residual of 1.5 mg/L after contact time. What initial chlorine dosage should be targeted, assuming the demand estimate is accurate?

12.0 mg/L

6.5 mg/L

9.5 mg/L

8.0 mg/L

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A sewer segment has recurring root intrusion at several pipe joints. Jet cleaning restores flow temporarily, but the problem returns within months. What is the best long-term response?

Add chlorine routinely to the sewer because chlorine will permanently prevent root penetration.

Inspect and repair or rehabilitate the defective joints or pipe that permit root entry.

Increase jet-cleaning frequency and continue using cleaning as the permanent corrective method.

Reduce upstream wastewater flow so roots have less moisture available around the pipe.

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A plant wants to determine whether its discharge is contributing to low dissolved oxygen in a receiving stream. Which monitoring approach is most informative?

Measure only influent temperature because temperature is the main cause of downstream oxygen changes.

Measure only chlorine residual in the aeration basin because it predicts receiving-stream oxygen conditions.

Collect representative upstream and downstream data together with effluent quality and flow information.

Collect only one effluent grab sample because the discharge itself is the only relevant location.

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A primary clarifier develops dark, septic sludge and gas bubbles that lift settled solids to the surface. Sludge has been withdrawn only once per day. What is the best corrective action?

Increase sludge-withdrawal frequency and prevent excessive sludge detention in the clarifier.

Reduce sludge withdrawal further so the blanket can compact.

Increase effluent chlorination to stop gas formation in the clarifier.

Return the primary sludge to the influent continuously.

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Rags and plastics begin appearing in downstream pumps and primary clarifier equipment after the headworks screen had previously removed them effectively. What is the best first investigation?

Raise the final chlorine dose so plastics and rags are disinfected before reaching downstream pumps.

Reduce digester mixing because excessive mixing can cause coarse debris to pass through screens.

Inspect the screen, rake or cleaning mechanism, and any bypass that could allow debris through.

Increase secondary-clarifier return sludge flow so rags are carried back to the aeration basin.

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On a centrifugal wastewater pump, the discharge valve is gradually throttled while suction conditions and pump speed remain unchanged. What generally happens to the pump's operating point?

Flow increases and discharge head decreases.

Both flow and discharge head remain unchanged.

Flow decreases and discharge head increases.

Both flow and discharge head increase.

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If the daily influent BOD load stays about the same while aeration-basin MLVSS inventory doubles, what happens to the food-to-microorganism ratio (F/M), assuming basin volume is unchanged?

It remains unchanged because flow and basin volume did not change.

It decreases to about one-half of its previous value.

It doubles because more microorganisms create more food.

It becomes zero because MLVSS is not part of the F/M relationship.

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Influent pH suddenly falls to 3.5, respiration in the aeration basin drops, and an industrial discharge is suspected. What is the most appropriate response?

Stop influent sampling until pH returns to normal so abnormal results do not affect the data set.

Increase return activated sludge because low influent pH usually means the biomass inventory is too small.

Increase chlorine feed because chlorine will reliably neutralize a strongly acidic industrial discharge.

Control the industrial source, protect the biological process, and follow pretreatment response procedures.

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An activated-sludge plant has a secondary clarifier with a high, fluffy sludge blanket and poor settling. The 30-minute settle test is high, and aeration-basin DO has been near 0.5 mg/L for several days. What is the best initial process response?

Increase final-effluent chlorination so chlorine contact will force the activated sludge to settle.

Reduce aeration further so filamentous organisms lose access to oxygen and the sludge becomes denser.

Stop return activated sludge flow so the clarifier can empty itself into the aeration basin.

Restore adequate aeration and evaluate loading and sludge-age conditions affecting settleability.

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A plant wastes 50,000 gal/day of sludge at 0.80% solids. A dewatering process captures 95% of the incoming solids and produces cake at 20% solids. Approximately how many wet tons of cake are produced per day? Use 8.34 lb/gal and 2,000 lb/ton.

1.6 tons/day

7.9 tons/day

4.0 tons/day

15.8 tons/day

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An RBC shaft stops rotating because of a drive failure. Why is prompt corrective action important?

Stopped rotation immediately raises influent BOD because the sewer receives less hydraulic resistance.

Stopped rotation increases chlorine residual because less chlorine is consumed by moving media.

Rotation alternates media exposure to wastewater and air, so stopping it reduces treatment effectiveness.

Stationary media improve oxygen transfer because the biofilm remains continuously exposed to air.

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A primary clarifier has poor suspended-solids removal even though the sludge blanket is normal. Flow observation shows most influent entering one side of the tank and short-circuiting toward the effluent weir. What should be corrected?

Return activated sludge concentration.

Influent distribution and baffling.

Chlorine contact time.

Digester gas mixing.

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An activated-sludge plant has low F/M, very long solids age, small pin floc in the final effluent, and minimal wasting. Which adjustment is most appropriate?

Gradually increase waste activated sludge removal to reduce excessive solids age.

Increase return sludge only, with no change in wasting.

Raise the chlorine dose to improve floc size.

Stop wasting entirely to build more old solids.

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A collection system shows a large wet-weather flow increase at the treatment plant while influent BOD concentration drops substantially. Which explanation best fits the data?

The aeration blowers are introducing excess oxygen into the influent sewer.

Infiltration and inflow are adding relatively dilute water and increasing hydraulic loading.

Primary sludge pumping is increasing the influent BOD concentration.

Industrial waste with very high organic strength is entering the sewer.

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An activated-sludge plant develops thick, persistent dark-brown foam. The solids retention time is much higher than the plant's normal target and wasting has been very low. Which response is most appropriate?

Reduce all aeration regardless of measured DO so the foam organisms receive less oxygen.

Confirm the foam cause and reduce excessive solids age by increasing wasting as appropriate.

Increase influent hydraulic loading with stormwater so the foam is physically washed away.

Stop wasting and allow solids age to increase further until the foam layer becomes heavier.

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A belt filter press suddenly produces wetter cake and cloudy filtrate. Polymer use was recently increased, but no bench testing was performed. What is the best next step?

Increase sludge feed rate until the press reaches hydraulic overload and forces water from the cake.

Increase polymer immediately because wetter cake always proves the previous dose was too low.

Bench-test conditioning and verify polymer preparation, feed concentration, and press settings.

Stop sludge conditioning because properly operated belt presses should not require polymer addition.

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A Texas domestic wastewater treatment facility is classified at a level that requires a Class B chief operator. Which staffing choice satisfies the minimum license-level requirement for the chief operator?

Assign an unlicensed supervisor as long as a Class B consultant is available by phone.

Assign a Class C operator because the operator has several years of plant experience.

Assign an operator who holds a Class B or Class A wastewater treatment license.

Assign any licensed wastewater collection operator regardless of treatment license class.

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A 30-minute settleometer test gives 450 mL/L settled sludge. MLSS is 3,000 mg/L. What is the approximate SVI, and what does it suggest?

450 mL/g; normal settling for most plants.

67 mL/g; severe bulking.

150 mL/g; relatively high SVI that warrants evaluation of settling conditions.

15 mL/g; extremely poor settling.

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A permit defines compliance with a monthly average BOD5 limit of 20 mg/L using four representative weekly results. The results are 18, 22, 19, and 25 mg/L. What should the operator conclude?

Only the highest weekly result is used, so the reported value is 25 mg/L.

The monthly average is 19 mg/L, so the limit is met.

The monthly average is 20 mg/L, so the limit is met.

The monthly average is 21 mg/L, so the monthly average limit is exceeded.

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During a BOD5 test, dissolved oxygen in a sample bottle is completely depleted before the end of the incubation period. What is the best response?

Repeat the analysis using an appropriate dilution so a valid oxygen-depletion measurement can be obtained.

Add chlorine to the bottle and continue the same test.

Report the BOD5 as zero because no oxygen remains.

Use the result without correction because complete depletion improves sensitivity.

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A trickling filter begins ponding on the media surface and the rotary distributor slows. What should the operator investigate first?

Clogged media, distributor nozzles, or underdrain restrictions that are limiting hydraulic passage.

Whether the laboratory incubator temperature is too high.

Whether primary sludge is being wasted too frequently.

Whether the final chlorine residual is too low.

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A wastewater pond has very high dissolved oxygen in late afternoon but very low dissolved oxygen just before sunrise. What best explains this pattern?

Daylight photosynthesis raises DO, while nighttime respiration lowers it before sunrise.

Daylight chlorination raises DO, while the chlorine residual disappears during the night.

Influent BOD approaches zero each night and then returns when daylight reaches the pond.

Sludge digestion produces oxygen during the day and consumes it after sunset.

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A utility manager directs the wastewater supervisor to reduce overtime without increasing compliance risk. What is the best implementation approach?

Cut staffing on every shift immediately, regardless of workload or operator qualification.

Allow unlicensed staff to fill licensed operating positions whenever overtime would otherwise occur.

Delay preventive maintenance so all available hours can be moved into routine operating rounds.

Review workload and qualifications, then adjust schedules and cross-training while preserving coverage.

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An aeration basin suddenly appears to have low dissolved oxygen, but the DO meter fails its calibration check in air. What should the operator do before making a major process change?

Increase aeration immediately and ignore the meter check.

Verify or repair the instrument and confirm the DO result with a reliable measurement.

Reduce return activated sludge flow to raise the indicated DO.

Increase wasting because low DO always means the sludge age is too high.

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A secondary clarifier sample settles well at first, but after standing the sludge rises with small gas bubbles. Aeration-basin nitrate is high. What is the most likely cause?

Denitrification in the clarifier is producing nitrogen gas that lifts settled sludge.

Excess chlorine in the aeration basin is creating oxygen bubbles.

Low influent temperature is causing sand to float.

Primary-screening failure is trapping rags in the clarifier.

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A discharge permit sets a daily maximum effluent TSS limit of 30 mg/L. A valid compliance sample measures 36 mg/L. What is the correct conclusion?

The result is not reportable unless a second sample also exceeds 30 mg/L.

The result is acceptable if influent TSS was unusually high that day.

The result is acceptable if the monthly average remains below 30 mg/L.

The result is a permit violation because the valid daily value exceeds the daily maximum.

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Influent organic loading drops sharply while MLSS and aeration rate remain unchanged. DO rises well above the plant's normal operating target. What process-control response is most reasonable?

Stop all wasting immediately regardless of solids age.

Increase aeration further because high DO proves oxygen demand is rising.

Reduce aeration carefully while continuing to monitor DO and treatment performance.

Increase chlorine dosage in the aeration basin.

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A permit has a monthly average flow limit of 1.50 MGD and no separate daily maximum flow limit. Four equally weighted reporting-period flow values are 1.20, 1.40, 1.70, and 1.30 MGD. Which interpretation is correct?

The permit is violated because one value is above 1.50 MGD.

The average is 1.40 MGD, so the stated monthly average flow limit is met.

The average is 1.50 MGD, so the plant must report a violation.

The average is 1.60 MGD, so the limit is exceeded.

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During storms, operators observe water pouring through several low manhole lids and the treatment plant receives severe hydraulic peaks. What corrective action most directly addresses this source of inflow?

Increase polymer dosage at the dewatering unit to compensate for the additional hydraulic loading.

Repair the affected manhole lids, seals, and other direct stormwater entry points.

Lower the final chlorine residual so more hydraulic capacity is available during the storm.

Increase aeration-basin solids concentration so the plant can absorb the additional stormwater volume.

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A centrifugal influent pump develops a gravel-like noise, vibration, and unstable flow. Suction pressure is lower than normal. What should the operator investigate first?

High return activated sludge concentration.

A suction-side restriction, low wet-well level, or another condition reducing available suction head.

Excessive chlorine residual in the plant effluent.

Whether the discharge valve can be throttled further to increase suction pressure.

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After a sharp peak-flow event, secondary effluent TSS rises and the clarifier sludge blanket climbs, but settleability tests remain normal. What is the most likely problem?

Hydraulic and solids loading are exceeding clarifier capacity, causing solids washout.

Excessive BOD test dilution is washing solids from the clarifier.

Chlorine demand is too low.

Low influent pH is always the cause of high effluent TSS.

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A reclaimed-effluent irrigation area begins ponding and producing runoff after several days of wet weather. What is the best immediate operating response?

Increase irrigation rate so the ponded water is forced into the saturated soil more quickly.

Reduce or stop application, prevent runoff, and resume when the site can accept the water.

Bypass the permitted disposal area and route excess reclaimed water to the nearest drainage channel.

Increase chlorine dose so any runoff leaving the application area automatically becomes acceptable.

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Chlorine feed rate has not changed, but the contact-basin residual falls while influent ammonia and organic loading increase. What is the most likely explanation?

Contact time has become irrelevant.

Chlorine demand has decreased.

Wastewater chlorine demand has increased.

The residual must be false because ammonia never affects chlorine demand.

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Why do wastewater collection-system design criteria include minimum-flow-velocity requirements?

To eliminate the need for access points such as manholes and cleanouts.

To keep every sewer line operating as a pressurized force main.

To make every gravity sewer flow completely full during normal operation.

To limit solids deposition and the maintenance problems caused by sluggish flow.

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A plant's final clarifier blanket is rising even though SVI remains acceptable. Operators find that one return activated sludge pump is out of service and actual RAS flow is far below the normal target. What should be done first?

Restore adequate RAS capacity and monitor the clarifier blanket and solids inventory.

Lower aeration-basin DO to force more settling.

Increase effluent chlorine residual.

Increase WAS sharply to remove all solids from the system.

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A plant treats 2.5 MGD and needs an 8.0 mg/L chemical dose. The chemical solution is 12.5% active by weight and weighs 10.0 lb/gal. Approximately how many gallons of solution are required per day? Use 8.34 lb per (mg/L·MGD).

16.7 gal/day

334 gal/day

133 gal/day

66.7 gal/day

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An anaerobic digester shows falling pH, rising volatile acids, and declining gas production after a rapid increase in feed. What is the best operating response?

Stabilize or reduce feed loading and restore digester balance while monitoring key operating conditions.

Add chlorine to suppress acid-forming bacteria and raise gas production in the anaerobic digester.

Increase feed rapidly so acid-forming and methane-forming organisms both receive more substrate.

Stop mixing permanently so volatile acids can settle away from the active digester biomass.

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An aerobic digester develops odors, poor volatile-solids reduction, and near-zero dissolved oxygen after an aeration-system failure. What should the operator do first?

Add chlorine to the digester so odor-producing organisms are destroyed before aeration resumes.

Stop all plant solids wasting indefinitely so less oxygen is needed in the aerobic digester.

Restore adequate aeration and verify oxygen transfer is sufficient for the current solids load.

Increase sludge feed to the digester so the added organic load stimulates oxygen transfer.

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A chlorine-room alarm activates and a strong chlorine odor is detected near the doorway. What should an operator who is not assigned as an emergency responder do first?

Stay out of the contaminated area, warn others, and initiate the facility's chlorine emergency procedure.

Enter with a dust mask to locate the leak.

Shut off all plant flow so no chlorine can enter the contact basin.

Open the door and use a portable fan before notifying anyone.

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A nitrifying activated-sludge plant has adequate aeration-basin DO, but effluent ammonia is rising. Laboratory data also show pH near 6.2 and very low alkalinity. Which condition is the most likely contributor?

High dissolved oxygen is preventing ammonia oxidation.

Low effluent chlorine residual is suppressing nitrifiers in the aeration basin.

Low pH and depleted alkalinity are limiting nitrification.

Excess alkalinity is accelerating nitrification too much.

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A dewatering system's polymer solution is being sent directly to the press immediately after mixing even though the product requires aging time. Cake solids decline and solids escape in the filtrate. What correction is most appropriate?

Increase sludge feed rate so stronger hydraulic loading compensates for weak polymer conditioning.

Raise plant chlorine dosage so the additional residual improves polymer activation at the press.

Restore the required polymer make-down and aging procedure before making further process changes.

Eliminate polymer use because wastewater sludge should dewater effectively without chemical conditioning.

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Under Texas domestic wastewater collection-system design criteria, what is the minimum nominal diameter for a gravity sanitary sewer collection pipe, excluding service laterals and special cases?

4 inches

8 inches

6 inches

10 inches

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