Grade IV Wastewater Treatment Plant Operator Exam

A plant wants to reduce energy cost without increasing compliance risk. Aeration is the largest electrical load. Which management approach is strongest?

Optimize aeration using process demand, DO control, blower efficiency, and treatment performance data

Replace the existing blowers with the highest-efficiency units before determining whether current controls are optimized

Lower the DO setpoint by the same amount on every shift and evaluate only whether blower kWh decreases

Reduce aeration during low-flow hours using a fixed schedule without checking ammonia or process response

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Maintenance must open a sludge pump that can start automatically from a remote control system. Which step is essential before the pump is opened?

Close the discharge valve and rely on the motor overload to prevent an unexpected restart

Notify the control room that maintenance is beginning and keep radio contact during the job

Place the local selector in OFF and post a warning sign at the control panel

Isolate all hazardous energy, apply lockout/tagout, and verify a zero-energy state before work

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A biological process removes 250 lb/day of ammonia nitrogen by nitrification. Using an oxygen requirement of 4.57 lb O2 per lb ammonia-N oxidized, approximately how much oxygen is required?

1,710 lb O2/day

1,140 lb O2/day

570 lb O2/day

860 lb O2/day

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A UV disinfection system shows declining dose delivery as UV transmittance falls and sleeve fouling increases. Which response is most appropriate?

Clean the UV sleeves and investigate upstream solids or water-quality conditions affecting transmittance

Replace the lamps first even if lamp age and output remain within the expected operating range

Lower the UV dose setpoint to compensate for the reduced transmittance and keep the same flow rate

Increase lamp output while postponing sleeve cleaning until the next scheduled maintenance interval

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A review of injury reports shows several different slips and falls in dewatering and chemical areas. What is the best Grade IV management response?

Focus first on refresher training because the incidents occurred in different work areas

Revise housekeeping assignments in the affected areas and review results at the next annual safety meeting

Analyze the recurring causes, correct site and work-practice hazards, and track whether the controls work

Increase inspection frequency and PPE enforcement without changing the underlying work practices

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A dewatering process is using more polymer, but cake solids are not improving and centrate TSS is increasing. What is the best optimization approach?

Adjust centrifuge operating settings first while holding polymer concentration and make-down conditions unchecked

Increase polymer dose until centrate TSS reaches its minimum value, then evaluate cake solids and cost

Reduce sludge feed rate until centrate improves, then retain the existing polymer dose as the new standard

Perform controlled dose trials while tracking feed solids, cake solids, capture, and centrate quality

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A toxic industrial discharge is suspected to be entering the plant and respiration rate in the activated sludge drops sharply. What is the best immediate process-control objective?

Increase aeration immediately to the maximum available rate so oxygen transfer offsets the toxic effect

Increase wasting to remove affected biomass before determining whether the toxic load is still entering the plant

Increase RAS flow to keep more biomass circulating through the aeration basin while the discharge passes

Protect the biological process by containing, diverting, or equalizing the slug where possible while intensifying monitoring

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An anaerobic digester shows increasing volatile acids, decreasing alkalinity, and a falling methane percentage. What does this pattern most strongly indicate?

The digester is becoming unstable because acid production is outpacing methane-forming activity

The digester is fully stabilized and should be fed at a higher rate immediately because the increased acids provide additional substrate for methane-forming organisms

The sludge is over-aerated and should be transferred to an anoxic basin

The gas meter is reading low because volatile solids destruction is complete

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A trickling filter develops ponding and the distributor nozzles show uneven flow. Which response best addresses both the symptom and likely cause?

Increase distributor speed while leaving the uneven nozzle flow and media condition unchanged

Restore uniform hydraulic distribution and investigate media plugging or biological overgrowth

Increase recirculation first to raise hydraulic shear across the filter surface without checking the distributor

Temporarily reduce hydraulic loading and wait to see whether ponding clears without inspecting the nozzles

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A facultative pond develops persistent dark color and strong anaerobic odors after a major organic load increase. What is the best operational interpretation?

The pond is receiving too little organic loading to sustain the facultative microbial population

The pond is being mixed too aggressively, causing the aerobic surface layer to become anaerobic

The pond is likely overloaded and oxygen demand is exceeding the system's available treatment capacity

The pond detention time has increased enough to favor complete stabilization and normal anaerobic odors

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A plant has recurring night-shift process upsets because operators are unsure who may change aeration, wasting, and chemical-feed settings when the supervisor is off site. What is the strongest supervisory response?

Allow each shift to develop its own response practices as long as permit limits are ultimately met

Restrict all process-control changes to the day shift and leave night-shift setpoints unchanged

Require operators to wait for the off-site supervisor's approval before making any process adjustment

Define decision authority and escalation limits, train the affected operators, and use a documented shift handoff process

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Primary effluent TSS is rising while the primary clarifier sludge blanket has become deeper than its normal operating range. What adjustment should be considered first?

Increase skimming frequency because a deeper sludge blanket is primarily a surface-scum problem

Decrease sludge withdrawal so the accumulated solids can compact before removal

Reduce influent flow through the clarifier to lower the hydraulic loading while leaving sludge withdrawal unchanged

Increase primary sludge withdrawal and verify that the withdrawal system is functioning properly

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A reclaimed-water train experiences a turbidity excursion that can compromise downstream disinfection performance. What is the best operator response?

Reduce the reclaimed-water delivery rate but continue supplying the system as long as disinfectant residual remains measurable

Protect the reuse system by holding, diverting, or otherwise preventing off-specification water from being delivered while correcting the cause

Wait for confirmatory microbiological results before taking action because turbidity alone does not require an operational response

Increase disinfectant dose and continue delivery while waiting for turbidity to return to normal

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Effluent ammonia rises while effluent BOD remains low and aeration-basin DO appears adequate. Which evaluation is most useful for distinguishing a nitrification-specific problem?

Evaluate settleability and RAS rate first because ammonia removal is primarily controlled by final clarification

Increase the influent carbon load to stimulate nitrifier growth before checking SRT or alkalinity

Review SRT, temperature, alkalinity, pH, toxicity indicators, and nitrifier performance trends

Review only aeration-basin DO because adequate bulk DO rules out other nitrification limitations

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Which approach provides the strongest basis for adjusting return activated sludge flow at a conventional activated-sludge plant?

Set RAS equal to WAS so the two sludge flows always remain hydraulically balanced

Use sludge blanket behavior, settling characteristics, solids inventory, and clarifier loading together

Use a fixed percentage of influent flow at all times regardless of clarifier conditions

Change RAS only when effluent BOD exceeds the permit limit

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A tertiary phosphorus-removal process uses metal salt addition before filtration. Which approach best supports efficient chemical control?

Optimize the dose only for minimum effluent phosphorus without considering pH, alkalinity, or added solids production

Use jar or process testing and monitor pH, alkalinity, phosphorus removal, and solids production while optimizing dose

Pace chemical feed only to influent flow because flow alone determines the required metal-to-phosphorus ratio

Hold a fixed design dose unless effluent phosphorus exceeds the limit, regardless of changes in alkalinity or influent phosphorus

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A pump delivers 1,200 gpm against 85 ft of total dynamic head at 72% overall efficiency. Electricity costs $0.16/kWh. Approximately what is the daily electrical cost if the pump runs 24 hours?

$171/day

$103/day

$137/day

$76/day

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A grit removal unit is producing material with an unusually high amount of putrescible organic matter. Which condition is most likely?

Aeration or velocity is high enough to keep most mineral grit in suspension

The grit chamber is providing too little detention time for mineral particles to settle

The upstream screen is passing an unusually high fraction of coarse organic debris

Flow conditions are allowing too many lighter organic solids to settle with the grit

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For a California Class IV wastewater treatment plant, what is the minimum grade level for the designated operator-in-charge under the standard classification table?

Grade IV

Grade I

Grade III

Grade II

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An activated-sludge plant has rising SVI, poor settling, and filamentous organisms observed microscopically. What is the best next step before selecting a control strategy?

Increase wasting enough to reduce SRT before confirming which operating condition is selecting for the filaments

Identify the process conditions favoring the filaments and correct those conditions using plant data

Increase RAS flow to lower the clarifier blanket and use settling improvement as the primary filament-control measure

Begin return-sludge chlorination immediately because filament control should precede identification of the cause

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A plant adds an anoxic zone ahead of the aerobic zone and returns nitrate-rich mixed liquor to it. What process objective does this modification primarily support?

Nitrification by providing a high-oxygen zone where ammonia is oxidized to nitrate

Biological denitrification by providing nitrate and a low-oxygen environment for nitrate reduction

Chemical phosphorus precipitation by increasing metal-salt contact with the mixed liquor

Enhanced biological phosphorus removal by providing an anaerobic zone with no nitrate recycle

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A nitrifying trickling filter loses ammonia removal after a major increase in soluble BOD loading. Dissolved oxygen is also lower than normal. What is the most reasonable explanation?

Alkalinity increased enough to suppress nitrifier activity despite the lower dissolved oxygen

Heterotrophic growth and oxygen demand increased, reducing conditions favorable for nitrifiers

The higher soluble BOD shortened media contact time even though oxygen availability did not change

The increased organic load caused nitrifiers to outgrow the heterotrophs and consume the available oxygen

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Seasonal reclaimed-water demand falls sharply, increasing storage time in the reuse system. What operational concern should receive greater attention?

Reduced storage mixing, because longer detention time normally eliminates stratification and biological growth

A lower disinfectant residual target, because reduced seasonal demand decreases the need for residual control

Water age, residual or disinfectant stability where applicable, algae growth, and storage turnover

Distribution pressure, because higher pressure is the primary control for limiting water age in storage

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Influent strength varies substantially over a 24-hour period, and management wants a representative daily BOD loading estimate. Which sampling approach is most appropriate?

Use the previous month's average BOD concentration with today's measured flow

Collect equal-volume grab samples only during the day shift when laboratory staff are present

Collect one grab sample at the expected peak hour and multiply the result by average daily flow

Use a properly preserved flow-proportional composite sample over the period of interest

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Why is reliable upstream turbidity control especially important when reclaimed water depends on a downstream disinfection process?

Turbidity matters only when reclaimed water is stored for more than one day before use

Low turbidity increases disinfectant demand because clearer water absorbs more disinfectant

High turbidity can shield microorganisms and reduce the reliability of disinfection performance

High turbidity affects filter headloss but does not materially affect downstream disinfection performance

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A sudden laboratory ammonia result is inconsistent with stable aeration-basin conditions, normal effluent nitrate, and unchanged online trends. What should the operator do first?

Reduce wasting to increase solids retention time in case nitrification is beginning to fail

Increase aeration temporarily and use the next routine laboratory result to judge whether the change helped

Verify sampling, preservation, holding time, calibration, and laboratory quality-control information before changing the process

Collect a confirmation sample immediately but make the process adjustment before the confirmation result is available

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Two duplicate TSS analyses from the same well-mixed sample differ far more than the laboratory's normal precision. What is the best interpretation?

Report the higher result while retaining the lower value only as a laboratory quality-control note

Repeat only the lower result because the higher value is more likely to reflect incomplete sample mixing

Average the two results and report the mean because duplicate analyses are intended to smooth random variation

The duplicate difference suggests an analytical or sample-handling problem that should be investigated

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An anaerobic digester produces 80,000 ft3/day of biogas that is 65% methane. If methane has a heating value of about 1,000 Btu/ft3, what is the approximate daily heat value of the methane produced?

40 million Btu/day

80 million Btu/day

52 million Btu/day

26 million Btu/day

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At a California Class IV wastewater treatment plant, what minimum staffing condition applies to the grade levels of the operator workforce under the current certification regulations?

At least 25% of the operators must hold Grade II or higher certificates

Every operator must hold Grade III or higher certification

Only the chief plant operator is subject to a minimum certification grade

At least 50% of the operators must hold Grade II or higher certificates

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A change in a California wastewater treatment plant's information may affect its plant classification. Under the current operator-certification requirements, when must the owner or chief plant operator submit the updated classification information?

Within 30 days of the change

Within 10 days of the change

At the next operator-certificate renewal

Within 60 days of the change

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During a high-flow event, a step-feed activated-sludge plant shifts more influent to downstream aeration zones. What is a principal process-control benefit of this strategy?

It increases the return-sludge concentration by sending more influent directly to the final clarifiers

It distributes organic and hydraulic loading through the basin rather than applying all influent at the head end

It lowers the total plant flow by storing part of the influent inside downstream aeration zones

It raises the system SRT automatically because downstream feed points reduce solids wasting

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A plant feeds polymer at 3.0 mg/L to a sludge stream of 4.0 MGD. Approximately how many pounds of polymer are required per day?

125 lb/day

150 lb/day

100 lb/day

75 lb/day

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Effluent ammonia is increasing during cold weather. Aeration-basin DO is low and the calculated SRT is near the minimum needed for nitrification. Which combined response is most appropriate?

Reduce wasting to raise SRT but leave the low dissolved oxygen condition unchanged

Increase aeration but leave the solids retention time unchanged even if it remains near the nitrification minimum

Increase RAS flow to raise MLSS without evaluating oxygen transfer or the actual SRT

Improve aeration and preserve sufficient solids retention time for the nitrifying population

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Primary sludge is becoming septic in the hopper and causing gas formation that interferes with settling. Which operating change best addresses the cause?

Reduce sludge withdrawal frequency so the hopper solids can thicken further before removal

Increase sludge withdrawal frequency to reduce the time solids remain in the clarifier

Increase influent mixing ahead of the clarifier to keep the settled sludge from becoming septic

Increase the withdrawal rate during the existing withdrawal periods without changing how long sludge remains between withdrawals

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A membrane tertiary system shows a steady rise in transmembrane pressure at the same production rate. What does this trend most directly indicate?

Membrane resistance or fouling is increasing and cleaning plus pretreatment performance should be evaluated

Membrane permeability is improving, allowing the same production rate to be maintained at a higher pressure

Feed temperature has increased enough to raise water viscosity and therefore increase the required pressure

Pretreatment solids removal has improved, increasing the solids load reaching the membrane surface

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A plant-wide solids mass balance does not close after a major process change. Before concluding that solids are being lost biologically, what should be done first?

Exclude changing solids inventories in basins and clarifiers because only external inputs and outputs belong in a plant mass balance

Verify the flow meters, sampling locations, solids analyses, time basis, and inventory assumptions used in the balance

Use design flows in place of measured flows so short-term instrument variation does not affect the balance

Adjust wasting until calculated solids output equals input, then use the new wasting rate as the operating target

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Headloss across a mechanically cleaned bar screen is rising and the upstream channel level is increasing. What is the most appropriate first operational response?

Increase aeration in the grit chamber to compensate for the higher upstream water level

Inspect the screen-cleaning mechanism and remove accumulated screenings or obstructions

Reduce primary sludge withdrawal so more solids remain in upstream treatment

Open the downstream bypass and leave the obstructed screen in service until the next shift

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Secondary effluent turbidity is increasing even though aeration-basin MLSS is stable. The final clarifier sludge blanket is rising. What should the operator evaluate next?

Increase RAS flow immediately to lower the blanket before checking settling characteristics or clarifier loading

Decrease RAS flow to retain solids in the clarifier longer and improve compaction

Clarifier solids loading, hydraulic loading, settling characteristics, and RAS/blanket control

Increase aeration-basin DO because a rising final-clarifier blanket is primarily an oxygen-transfer problem

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Two replacement pumps meet the required hydraulic duty. Pump A costs less to purchase, while Pump B has higher efficiency and lower projected maintenance cost. What is the best budget decision method?

Delay replacement until failure so the actual emergency cost can be compared with the projected replacement cost

Compare life-cycle costs, reliability, energy use, maintenance, and required performance before selecting

Select Pump A because the lower purchase price provides the clearest near-term budget savings

Select Pump B based on efficiency alone because lower energy use will offset other cost differences

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A stabilization pond has high afternoon pH and dissolved oxygen but much lower dissolved oxygen just before sunrise. What best explains this daily pattern?

Wind mixing raises pH during the afternoon and stops biological respiration after sunset

Nitrification is strongest in daylight and produces oxygen that is consumed during the night

Warmer afternoon water holds more dissolved oxygen, while cooler nighttime water releases it to the atmosphere

Algal photosynthesis raises oxygen and pH during daylight, while nighttime respiration consumes oxygen

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A tertiary granular-media filter is approaching its established terminal headloss while effluent turbidity remains acceptable. What is the best operating response?

Backwash according to the established terminal headloss or operating criterion before breakthrough occurs

Continue the run until turbidity begins to rise because turbidity breakthrough should determine every backwash

Increase coagulant dose to hold turbidity down while allowing headloss to continue increasing

Reduce the filter rate and continue operating beyond the terminal headloss criterion as long as turbidity remains acceptable

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A tertiary filter treats 2.4 MGD through a total active filter area of 12,000 ft². What is the hydraulic loading rate in gallons per day per square foot?

500 gal/day/ft²

50 gal/day/ft²

100 gal/day/ft²

200 gal/day/ft²

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After a sustained flow increase, a chlorine contact basin shows the usual measured residual but microbiological performance worsens. What should be investigated first?

Effective contact time and short-circuiting under the new hydraulic condition

The dechlorination dose downstream of the contact basin because it controls microbial inactivation inside the basin

A higher chlorine dose to restore the previous chlorine residual-to-flow ratio even though the measured residual is unchanged

Chlorine-feed calibration and residual-analyzer accuracy, with no hydraulic evaluation unless residual also changes

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Chemical spending decreased 12% this quarter, but effluent variability and corrective maintenance both increased. Which conclusion is most defensible?

The chemical program is successful because the line-item chemical budget is below the quarterly target

The chemical dose should remain at the reduced level until annual budget review even if process variability continues

The higher corrective-maintenance cost should be evaluated separately because it belongs to a different budget account

The cost reduction should be evaluated together with treatment performance, maintenance, risk, and total operating cost

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An activated-sludge system has excessively old sludge, good nitrification, and increasing endogenous conditions. What is the most appropriate controlled adjustment?

Increase wasting gradually and track the resulting SRT, settling, nutrient removal, and effluent performance

Increase RAS flow to reduce sludge age without changing the actual solids mass wasted from the system

Reduce wasting because endogenous conditions indicate the biomass needs a longer solids retention time

Increase wasting sharply based on the current MLSS concentration and evaluate SRT after the new MLSS stabilizes

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After a new SOP is issued, several operators perform the critical procedure differently. What is the best training response?

Allow supervisors to coach operators informally without defining or documenting the expected performance standard

Provide task-specific training, require demonstrated competency, and document follow-up where needed

Use a written quiz as the only competency check because the procedure is already described in the SOP

Repeat classroom instruction for the SOP and document attendance as evidence that the procedure is understood

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A plant has had two recent hydrogen sulfide alarms during permitted entries into the same wet well. Before authorizing another entry, what is the most appropriate supervisory action?

Shorten the planned entry time so the crew is exposed to the wet well atmosphere for fewer minutes

Allow entry if each entrant carries a personal gas monitor and leaves when an alarm occurs while the existing permit remains valid for the task

Reevaluate the entry hazard assessment, ventilation, monitoring, rescue provisions, and permit controls before entry

Require a second attendant at the opening while keeping the existing entry procedure unchanged

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A thickener receives 100,000 gal/day of sludge at 2.0% solids and produces 20,000 gal/day of underflow at 8.0% solids. Using 8.34 lb/gal, approximately what percent of incoming solids are captured in the underflow?

80%

70%

90%

60%

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A centrifuge suddenly loses solids capture after a polymer make-down system change. Which check should receive early priority?

Verify polymer concentration, aging/maturation, feed condition, and centrate response before increasing dose

Increase polymer feed rate based on pump speed while assuming the make-down concentration remained unchanged

Reduce differential speed to increase solids residence time before confirming that conditioning is adequate

Increase bowl speed to improve capture before checking whether the make-down change altered polymer strength

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Management wants to determine whether a new aeration-control strategy actually improved treatment efficiency. Which evaluation method is strongest?

Compare one day before and one day after the change using the same daily average effluent results

Change the aeration control and wasting strategy at the same time so the combined response can be evaluated under the new operating condition

Define performance indicators, control other major variables where practical, and trend results over an adequate response period

Use energy consumption as the primary measure and check effluent quality only if energy use improves

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