WPI Standardized Wastewater Treatment Operator Class II

A chronic WET report shows reduced reproduction in the effluent treatments, but reproduction is also below the method acceptability criterion in the dilution-water control. What is the immediate interpretation?

Pool the unacceptable control with earlier controls to meet the acceptance criterion.

Use the treatment-to-control difference as a valid estimate of effluent toxicity.

Treat the test as invalid for toxicity interpretation because the required control reproduction criterion was not met.

Use normal control survival to accept the reproduction endpoint despite its failed criterion.

Report this question (opens in a new tab)

After a sodium bisulfite feed change, final free chlorine becomes nondetect while total residual is also nondetect. The downstream dissolved oxygen decreases unexpectedly. Which possibility should be checked?

Loss of upstream chlorination is reducing the amount of bisulfite needed.

Insufficient bisulfite delivery is leaving an oxidizing chlorine residual.

Poor bisulfite mixing is leaving untreated chlorinated pockets at the final sampling point.

Excess bisulfite feed may be exerting oxygen demand beyond that needed for dechlorination.

Report this question (opens in a new tab)

One basin DO probe reads 0.6 mg/L, but a calibrated portable instrument nearby reads 2.3 mg/L and the online probe membrane is heavily fouled. Which step is most appropriate?

Raise RAS flow to reduce oxygen demand in the aeration basin.

Service and verify the online sensor before making a large aeration setpoint change.

Increase aeration based on the low online DO indication, then evaluate whether ammonia removal and blower energy change as expected.

Increase wasting to lower the aeration-basin oxygen demand.

Report this question (opens in a new tab)

An open-channel ultrasonic meter shows erratic low flows only when the upstream flume has visible deposits and water-level turbulence. Which corrective check is most appropriate?

Inspect primary-element geometry and sensor location, then verify flow against a reference.

Verify the analog output scaling against the SCADA engineering units.

Verify the flow-totalizer clock, its logging interval and accumulated pulse count against an independent timing reference.

Verify that the programmed flume dimensions match the installation records.

Report this question (opens in a new tab)

A sludge transfer pump moves 500 gal/min (31.5 L/s) against 80 ft (24.4 m) of total dynamic head. Assume a relative density (specific gravity) of 1.00. Measured shaft input is 20 hp (14.9 kW). Using 3,960 in the US hydraulic horsepower equation, what is the approximate pump efficiency?

51%

80%

63%

40%

Report this question (opens in a new tab)

A 30-minute settled-sludge test forms a clear supernatant, but the actual secondary clarifier discharges floating sludge clumps containing gas bubbles. Effluent nitrate is elevated. What mechanism merits focused investigation?

Denitrification in the clarifier blanket can lift settled sludge to the surface.

Filamentous bulking is preventing the floc from settling initially.

A high hydraulic overflow rate is carrying unsettled floc over the weirs.

Excessive aeration is entraining oxygen bubbles that remain trapped through clarification.

Report this question (opens in a new tab)

Personal monitoring during an 8-hour shift records 4 ppm of a gas for 2 hours, 1 ppm for 4 hours, and 0 ppm for 2 hours. Ignoring any short-term or ceiling criteria, what is the arithmetic 8-hour time-weighted average?

1.0 ppm

2.0 ppm

2.5 ppm

1.5 ppm

Report this question (opens in a new tab)

A blower has stable discharge pressure and flow, but one aeration basin lane shows persistently low dissolved oxygen while an adjacent lane is normal. Which field check best discriminates a distribution fault?

Compare lateral valve positions and air delivery or diffuser condition in the affected lane.

Compare the oxygen uptake rates of mixed liquor from the two lanes.

Compare the actual influent loading and mixed-liquor oxygen uptake in the two lanes during the same operating interval.

Cross-check the lane DO readings with a calibrated portable meter.

Report this question (opens in a new tab)

A mixer motor is normally supplied from a motor control center but can also receive power from a standby transfer switch. What should the authorized crew verify before hands-on maintenance?

Lock the local control selector and verify that the generator is not running.

All normal and alternate energy sources are isolated and zero energy is verified.

Disable automatic transfer and verify that the normal start command is absent.

Open the normal utility disconnect, test the MCC control selector and assume the generator transfer switch will remain in its normal position.

Report this question (opens in a new tab)

A plant pump delivers less flow at the same speed, makes a crackling noise, and has a fluctuating suction pressure. The wet-well level is lower than during normal operation. Which diagnosis should be investigated first?

Inadequate net positive suction head caused by lower suction conditions.

A damaged coupling reducing transmitted shaft speed.

Impeller wear increasing internal recirculation losses.

Excessive discharge head moving the pump toward shutoff.

Report this question (opens in a new tab)

An operator preparing to enter a designated permit-required digester vault obtains a normal oxygen reading at the top of the opening. Which additional action is still necessary before entry?

Complete the entry permit using the top oxygen reading and rely on the entrant to identify changing hazards.

Check combustible gas at the opening and use that reading to rule out toxic exposure.

Follow the entry permit and required atmospheric testing and protective measures throughout the space.

Check oxygen at the work level and use ventilation to address all remaining atmospheric hazards.

Report this question (opens in a new tab)

A permitted U.S. wastewater facility discovers an unplanned bypass with possible permit implications. Which action best preserves compliance while the investigation continues?

Document the event after normal treatment resumes and decide on notification from effluent appearance.

Complete an internal maintenance report and include the event in the next routine regulatory submission.

Estimate the bypass volume and defer notification until laboratory results establish its effects.

Initiate the site permit-notification procedure and preserve event, monitoring and response records.

Report this question (opens in a new tab)

In a chlorinated effluent contact basin, measured residual meets the plant target but peak flow has doubled and the basin operating volume is unchanged. What additional factor is essential before concluding disinfection is adequate?

Influent chlorine demand measured before the peak-flow period.

Use the historical daily chlorine dose and original basin design detention time to estimate contact exposure during the peak.

Total daily chlorine use divided by the daily wastewater volume.

Effective hydraulic contact time and short-circuiting at the higher flow.

Report this question (opens in a new tab)

After an industrial discharge, aeration-basin DO drops from 2.0 to 0.7 mg/L while blower air delivery remains steady. Influent soluble BOD increases, and pH is stable. What is the most likely immediate process explanation?

An increase in oxygen solubility at unchanged aeration and temperature.

Increased biological oxygen demand from the higher biodegradable organic load.

A reduction in biodegradable substrate available to the biomass.

A decrease in respiration associated with substrate inhibition.

Report this question (opens in a new tab)

A wet-well level transmitter reads 8.2 ft, while a recently verified local staff gauge reads 5.0 ft; the pump starts earlier than expected. Which test best identifies a measurement-chain fault?

Compare transmitter output, scaling, and the local gauge at multiple stable levels.

Check pump motor current against the expected hydraulic loading.

Compare check-valve closure time with the pump stop sequence.

Measure pump discharge flow at the present operating level.

Report this question (opens in a new tab)

A gravity thickener has increasing solids blanket depth and more suspended solids in overflow while the feed concentration remains stable. Underflow pumping has been below the planned rate. Which response most directly targets the imbalance?

Increase polymer dose while retaining the reduced underflow withdrawal rate.

Restore controlled underflow withdrawal and monitor overflow and blanket response.

Extend feed-thickening time ahead of the gravity unit in an attempt to increase its settled solids concentration before adjusting withdrawal.

Increase feed rate to compress the thickener blanket more rapidly.

Report this question (opens in a new tab)

A centrifuge shows a rapid increase in vibration after a feed-solids increase; bowl speed and differential speed are otherwise unchanged. What should be evaluated before increasing feed rate further?

Polymer demand and the clarity of centrate from a jar-test series.

Solids loading, cake discharge, and any imbalance or buildup inside the machine.

Centrate ammonia concentration and the associated sidestream nutrient load.

Feed temperature and the polymer solution aging time.

Report this question (opens in a new tab)

During a plate-and-frame filter press cycle, filtrate starts clear but solids later appear at the outlet associated with one plate. Feed characteristics and polymer preparation are unchanged, and no comparable change occurs at the other plates. What action best addresses a suspected localized bypass?

Stop and depressurize as directed, then inspect cloth seating, sealing faces, and plate alignment.

Extend the final pressing interval to increase cake solids.

Increase polymer dose after a feed-conditioning check to make stronger floc throughout the press, even though bypass is localized.

Reduce feed-solids concentration to lower the solids load per cycle.

Report this question (opens in a new tab)

An air-lift grit removal system has normal air supply pressure and flow, but grit accumulates in the channel and the discharge carries little solids. What is the most useful targeted inspection?

Hold the grit channel at lower flow while leaving the air-lift pickup position unchanged.

Run the upstream screen rake more frequently to intercept larger debris before it enters the grit channel.

Raise the air-lift supply pressure before confirming the nozzle and discharge are unobstructed.

Check the grit pickup nozzle, suction path, and underflow restriction for plugging.

Report this question (opens in a new tab)

An activated-sludge plant shows rising effluent ammonia. DO, temperature, and solids age remain within the established range for nitrification, with no known change in industrial discharge. Aeration effluent pH has fallen and alkalinity is nearly exhausted. Which factor is most directly supported by these observations?

Diffuser fouling could be limiting oxygen transfer at the floc scale even though the mixed-liquor DO and solids age appear satisfactory.

Insufficient alkalinity and pH buffering may be suppressing nitrifier activity.

Inhibition of nitrifiers by a newly introduced toxic industrial compound.

Cold-water washout of nitrifiers at the current solids age.

Report this question (opens in a new tab)

A plant using an anaerobic selector for biological phosphorus removal begins showing elevated effluent orthophosphate. The selector receives substantial nitrate in the RAS, while other operating conditions remain similar. What is a plausible mechanism?

Nitrate entering the anaerobic selector changes oxidation-reduction conditions but is assumed not to compete for influent carbon.

Nitrate prevents aerobic phosphorus uptake by removing oxygen from the aeration air.

Nitrate increases fermentation of influent carbon into volatile fatty acids.

Nitrate entering the anaerobic zone can consume readily available substrate and hinder EBPR conditions.

Report this question (opens in a new tab)

An online ammonia analyzer abruptly reports elevated final-effluent ammonia. A grab collected at the analyzer sampling point at the same time remains near baseline when tested by a laboratory method with acceptable calibration and QC. Which step is most defensible?

Investigate alkalinity depletion as the established cause of both measurements.

Increase solids age to compensate for an assumed loss of nitrifiers.

Check analyzer sampling, reagent condition and calibration against a verified standard.

Increase aeration based on the online ammonia signal and use the corrected grab-test value afterward to judge whether nitrification recovered.

Report this question (opens in a new tab)

At 1.5 MGD (5,678 m3/day), a dechlorination trial requires 1.2 mg/L of active reagent. The purchased product is 40% active ingredient by mass. Ignoring additional safety factors, approximately how much commercial product is required per day?

37.5 lb/day (17.0 kg/day)

15.0 lb/day (6.8 kg/day)

25.0 lb/day (11.3 kg/day)

93.8 lb/day (42.5 kg/day)

Report this question (opens in a new tab)

Effluent ammonia increases as nitrate decreases, with aeration DO stable but the mixed-liquor temperature substantially lower than the prior week. What additional data best help assess potential loss of nitrification?

RAS flow and clarifier blanket depth without checking biomass retention.

SRT and alkalinity trends together with a verified ammonia-nitrogen profile.

Aeration airflow and blower power without checking the nitrogen measurements.

Influent BOD and effluent turbidity without checking nitrogen conversion.

Report this question (opens in a new tab)

In a step-feed aeration system, the first inlet zone is oxygen limited while later zones have excess DO. Total blower delivery is adequate. Which control review most directly addresses the imbalance?

Compare step-feed wastewater distribution and zone air delivery against local oxygen demand.

Move all step-feed influent toward the first inlet to supply more substrate to the oxygen-limited zone.

Change total plant loading so the final zone has greater demand rather than correcting feed split.

Increase the rate of activated-sludge wasting to redistribute oxygen demand across the step-feed zones.

Report this question (opens in a new tab)

A laboratory reports BOD5 of 38 mg/L and CBOD5 of 21 mg/L on the same treated-effluent sample, both with acceptable QA. What is the most defensible interpretation?

The difference directly measures ammonia-nitrogen concentration in mg/L.

The sample has a higher biodegradable carbon concentration in the BOD5 bottle.

Use the ratio of COD to BOD5 as an indirect measure of nitrogenous oxygen demand instead of interpreting the paired inhibited tests.

Oxygen demand associated with nitrification contributed to the higher BOD5 result.

Report this question (opens in a new tab)

A sludge withdrawal isolation valve still turns but cannot fully seat, and a planned pump repair requires positive hydraulic isolation. What should be established before authorizing the repair?

Proceed after tagging the handwheel because an almost-closed indication is sufficient evidence of a hydraulic isolation boundary.

Provide and verify a reliable alternative isolation method under the work procedure.

Treat the valve as operable because its position indicator reaches nearly closed.

Increase downstream pump discharge pressure to help press the valve disc closed.

Report this question (opens in a new tab)

Primary-clarifier effluent TSS rises while influent TSS and basin flow remain stable. Sludge withdrawal has been intermittent and the sludge blanket is elevated. Which operating change best targets the observed mechanism?

Increase the frequency of scum removal from the surface.

Decrease sludge pump run time to encourage heavier solids consolidation in the basin.

Restore effective sludge withdrawal while monitoring blanket depth and effluent solids.

Reduce the chemical coagulant dose to limit solids entering the blanket.

Report this question (opens in a new tab)

A secondary clarifier has a deepening sludge blanket, but the settling test remains good and the RAS pump is below its normal operating range. Influent flow is unchanged. What is the most directly supported adjustment?

Lower the clarifier influent baffle to increase downward velocity through the blanket.

Reduce RAS further so sludge can concentrate longer before returning to aeration.

Restore adequate RAS withdrawal and track blanket depth and return-solids behavior.

Increase WAS first to eliminate sludge mass without restoring the return pathway.

Report this question (opens in a new tab)

A plant equalization basin is nearly empty at dawn but reaches high level every afternoon, even though the flow to secondary treatment fluctuates strongly. Which adjustment best uses the basin as intended?

Increase wasting from secondary clarification each time the influent flow rises.

Match the equalization discharge immediately to each influent peak so the basin remains empty.

Review influent pattern and control the basin discharge to attenuate downstream peak flow.

Keep the transfer pump continuously at maximum flow to protect the basin from high level.

Report this question (opens in a new tab)

A metering pump feeds a non-gas-evolving chemical solution from a replacement drum of the same product strength. The measured liquid discharge per minute falls at unchanged stroke rate and stroke length, and bubbles appear in the suction tubing. Which check most directly investigates the observed loss of delivery?

Look for an air leak or loss of prime at the suction connections and foot valve.

Check whether increased process flow has reduced the applied chemical dose.

Evaluate viscosity and chemical properties of the replacement drum to see whether the same-strength solution changed suction-line resistance.

Check whether the downstream residual analyzer has developed a calibration bias.

Report this question (opens in a new tab)

A delivery of sodium hypochlorite arrives while a storage-tank area also contains an acid cleaning chemical. The secondary-containment arrangement is unclear. What is the appropriate operational check?

Confirm the product label and rely on color-coded hoses without tracing the receiving line.

Verify hose fittings and retain shared containment as long as the two tanks remain closed.

Confirm compatible segregation and transfer routing using the SDS and facility procedure.

Confirm tank capacity and rely on separate containers within shared containment.

Report this question (opens in a new tab)

After a duty pump stops, its discharge line briefly reverses flow and the header pressure surges. The parallel pump is operating normally. What inspection most directly addresses the likely defect?

Inspect the stopped pump suction strainer for accumulated screenings.

Inspect the stopped pump discharge check valve for delayed or incomplete closure.

Inspect the operating pump impeller for erosion that reduces developed head.

Inspect the discharge isolation valve for a restriction during forward flow.

Report this question (opens in a new tab)

A mechanical bar screen has a rising upstream level, but the downstream channel level and incoming flow are stable. The drive runs and debris still collects against the bars. Which observation would most directly distinguish ineffective raking from a high downstream restriction?

Rake-to-bar contact and the amount of screenings actually carried over the discharge.

Measure motor-current variation over a complete rake cycle and compare it with earlier baseline traces from effective screening operation.

Compare the cleaning-cycle timer with the normal screen sequence.

Inspect the downstream gate position and channel water-surface profile.

Report this question (opens in a new tab)

An oxidation ditch shows adequate average DO but settled solids accumulate in one channel reach after an aerator is throttled. What operating property needs direct confirmation?

Effluent ammonia removal averaged over the entire ditch.

Rebalance average dissolved oxygen across the oxidation ditch through aeration setpoints while leaving local mixing velocity unmeasured.

Local channel velocity and mixing sufficient to keep biological solids suspended.

Average solids age calculated from daily wasting and effluent solids.

Report this question (opens in a new tab)

An aerobic digester receives a larger waste-activated-sludge feed than before. Dissolved oxygen and temperature remain within the facility operating targets, but volatile-solids reduction has declined, the digester discharge rate has increased, and calculated solids retention time is shorter. Which operating adjustment best addresses the evidence?

Reduce or redistribute the solids feed to restore adequate retention time while maintaining effective aeration and mixing.

Increase digested-sludge discharge to create more hydraulic capacity while keeping the incoming sludge loading at its new rate.

Raise aeration beyond the established DO target to compensate for the reduced digester retention time while preserving the higher feed rate.

Add dilution water to the digester so the feed becomes less concentrated without changing the total sludge mass entering each day.

Report this question (opens in a new tab)

A generator completes its weekly unloaded exercise, but during a supervised transfer test the clarifier drive starts and a large blower fails to accelerate. What additional check is most informative?

Verify generator no-load frequency and steady-state voltage again while disconnecting other motors from the standby transfer bus.

Compare generator fuel use during the unloaded exercise with previous tests.

Evaluate starting kVA, voltage dip, and sequencing during representative load transfer.

Compare the blower full-load running kW with the generator continuous kW rating.

Report this question (opens in a new tab)

A plate-and-frame press has intact cloths and sound plate seals, but cake solids decrease after polymer dose is reduced; filtrate remains mostly clear. What should be checked before modifying cycle pressure?

Plate gasket wear and the extent of visible leakage during pressing.

Filtrate-pump capacity and the final effluent discharge rate.

Conditioning dose and mixing effectiveness against actual sludge characteristics.

Inspect hydraulic pressing pressure and cycle duration for early termination despite intact seals and acceptable filtrate clarity.

Report this question (opens in a new tab)

A secondary clarifier treats a plant effluent flow of 0.90 MGD (3,407 m3/day), excluding return activated sludge. Its liquid surface area is 4,500 ft2 (418 m2). Using the plant effluent flow, what is its approximate surface overflow rate?

200 gal/day/ft2 (8.2 m/day)

250 gal/day/ft2 (10.2 m/day)

150 gal/day/ft2 (6.1 m/day)

320 gal/day/ft2 (13.0 m/day)

Report this question (opens in a new tab)

A high-level overflow alarm recurs at the influent pump station during peak wet-weather flow, but response logs show inconsistent calls and delayed dispatch. Which administrative improvement addresses the demonstrated failure?

Raise the high-level alarm threshold to reduce the frequency of calls.

Assign a weekly review of overflow totals without changing the callout sequence.

Add more frequent level readings to the log without assigning dispatch responsibility.

Test escalation contacts and clarify response ownership and callout steps in the SOP.

Report this question (opens in a new tab)

Influent flow is 0.85 MGD (3,217 m3/day) and BOD5 concentration is 210 mg/L. Approximately how much BOD5 enters the plant each day?

1,790 lb/day (812 kg/day)

1,490 lb/day (676 kg/day)

1,160 lb/day (526 kg/day)

1,260 lb/day (572 kg/day)

Report this question (opens in a new tab)

An RBC stage has uneven shaft rotation, rising gear reducer temperature, and an unchanged wastewater flow. What should be checked first under the approved isolation procedure?

Media wetting and wastewater distribution across the RBC stages.

Dissolved oxygen and soluble BOD through the RBC stages.

Sloughed-solids loading and downstream clarifier blanket depth.

Bearing condition, alignment, lubricant condition, and mechanical loading of the shaft.

Report this question (opens in a new tab)

A secondary clarifier bridge repeatedly trips on torque while the sludge blanket is unusually high. No drive fault is recorded when the basin is empty for maintenance. Which plant observation best helps determine if the trip is process-related?

Compare the clarifier drive alignment and gearbox lubrication records.

Compare the torque-switch calibration with its documented test results.

Track blanket depth and sludge withdrawal performance at the time of the torque alarm.

Compare the drive motor insulation resistance with its previous readings.

Report this question (opens in a new tab)

A trickling filter shows localized ponding and persistent odors, with recirculation flow within its normal range. Underdrains contain accumulated solids and airflow appears restricted. What action best targets both observations?

Increase recirculation to improve media wetting while leaving the drainage path unchanged.

Increase surface ventilation while retaining the existing underdrain solids deposits.

Evaluate underdrain drainage and ventilation, and remove obstructions under procedure.

Adjust distributor speed to improve surface distribution before clearing the underdrains.

Report this question (opens in a new tab)

A 30-minute mixed-liquor settling test produces 800 mL/L of settled sludge. MLSS is 2,500 mg/L. What is the approximate sludge volume index (SVI)?

125 mL/g

200 mL/g

320 mL/g

500 mL/g

Report this question (opens in a new tab)

A plant instrument-air receiver pressure recovers slowly after valve actuations, although the compressor runs continuously. Moisture is present in several actuator air lines. Which combined check best explains the fault?

Check instrument-air regulator settings at individual actuators.

Check for leaks, dryer failure, and reduced compressor delivery under load.

Check actuator travel stops and position-feedback calibration.

Check control-signal tuning and valve-positioner deadbands.

Report this question (opens in a new tab)

A UV channel reports normal electrical power but declining UV intensity and increasing effluent UV transmittance. The lamp operating hours are still within the scheduled interval. What should the operator assess?

Check whether increased suspended solids are shielding organisms despite the measured transmittance.

Sensor verification and quartz sleeve condition before replacing lamps by age alone.

Check whether an increase in UV-absorbing dissolved material is reducing light transmission.

Check whether higher channel flow is shortening exposure time rather than reducing the intensity reading.

Report this question (opens in a new tab)

SCADA displays a valve OPEN while a field limit switch and local indicator both show CLOSED. The PLC command bit is OPEN. What conclusion is best supported?

An OPEN command does not establish valve position; verify actuator and feedback circuits.

The disagreement establishes loss of communication between the PLC and SCADA.

The disagreement establishes a mechanical failure of the valve stem.

The disagreement establishes a failed actuator motor.

Report this question (opens in a new tab)

A facultative lagoon develops strong odors and low near-surface DO shortly after an abrupt weather-driven mixing event. Which observation would help determine whether reduced stratification has brought anaerobic bottom water into the surface layer?

Compare depth profiles of DO and temperature before and after the event.

Compare average hydraulic loading with the lagoon design loading.

Compare influent BOD loading before and after the weather event.

Compare algal abundance and daylight conditions across the weather event.

Report this question (opens in a new tab)

Tertiary-filter effluent turbidity rises after a prolonged run, while headloss across the bed is above its normal endpoint. Influent quality is unchanged. What should be evaluated next?

Verify backwash effectiveness and media condition before extending the filter run.

Extend the filtration run until the next scheduled low-flow period.

Increase coagulant dose to retain more solids in the loaded bed.

Increase filtration rate to recover lost treatment capacity during the run.

Report this question (opens in a new tab)