Wastewater Treatment Operator Certification Exam: Questions and Answers, Exams of Public Health

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WASTEWATER TREATMENT OPERATOR CERTIFICATION EXAM LATEST

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What causes frothing? - CORRECT ANSWER- Excessive solids retention time Describe oxidation ditches - CORRECT ANSWER- Modified form of activated sludge process Operated in extended aeration mode What are the major components of an oxidation ditch? - CORRECT ANSWER- Aeration basin Brush rotor assembly Settling tank Return sludge pump Excess sludge handling facilities Typical velocity in an oxidation ditch - CORRECT ANSWER- 1.0-1.5 ft/sec How is the rotor submersion level controlled in an oxidation ditch? - CORRECT ANSWER- Level control weir Typical MLSS concentration of an oxidation ditch - CORRECT ANSWER- 2000 - 6000 mg/L

Typical organic loading of an oxidation ditch - CORRECT ANSWER- 10 - 50 lbs BOD/day/1000 cu ft Typical F/M ration at an oxidation ditch - CORRECT ANSWER- 0.03-0.1 lb BOD/day/lb MLVSS Typical sludge age at an oxidation ditch - CORRECT ANSWER- 20 - 35 days Ideal DO level in an oxidation ditch - CORRECT ANSWER- 0.5-3.0 mg/L How long should it take to develop ideal MLSS concentrations in an oxidation ditch? - CORRECT ANSWER- 3 - 15 days Typical analyses for an oxidation ditch plant - CORRECT ANSWER- Settleable solids DO (upstream of rotor) pH Residual chlorine (final effluent) BOD COD Suspended solids Volatile solids Total solids Microscopic observation F/M (lbs BOD/day/lb MLVSS) = - CORRECT ANSWER- BOD (lbs/day) / MLVSS (lbs)

MLVSS (lbs) = - CORRECT ANSWER- Volume (MG) x MLSS (mg/L) x VM (%) x 8. lbs/gal Sludge age (days) = - CORRECT ANSWER- Solids under aeration (lbs) / Solids added (lbs/day) Advantages of treating wastewater with ponds - CORRECT ANSWER- Doesn't require extensive equipment Economical construction Doesn't require highly trained operators Treatment is equal to conventional processes Adaptable to changing loads Little energy consumption Wildlife habitat Few sludge handling problems Limitations of treating wastewater with ponds - CORRECT ANSWER- May produce odors Requires a large area of land Treats waste inconsistently depending on climate May contaminate groundwater May leave high levels of suspended solids in effluent Describe daily pH fluctuations in an aerobic pond - CORRECT ANSWER- Algae use CO2 during the day (increase pH)

Algae produce CO2 during the night (decrease pH) Describe anaerobic fermentation - CORRECT ANSWER- Acid formers first convert organic matter to CO2, Nitrogen, and organic acids Methane fermenters then break down acids into methane, CO2, H2S, alkalinity, and H Typical BOD removal of ponds - CORRECT ANSWER- 50 - 90% (70-80% for facultative ponds) Typical detention time in a facultative pond - CORRECT ANSWER- 50 - 60 days What is the single best preventative measure against emergent growth in a pond?

• CORRECT ANSWER- Maintain a water depth of at least 3 ft What are some ways to eliminate algae from pond effluent? - CORRECT ANSWER- Baffles Microscreening Slow sand filtration Dissolved air flotation Algae harvesting Centrifuges Chemical coagulation Magnetic separation

What are the major operational strategies of ponds? - CORRECT ANSWER- Maintain constant water elevation Distribute inflow equally Keep levees and dikes in good condition Observe and test pond condition Why should each pond be given routine pH and DO tests? - CORRECT ANSWER- Ponds have clearly develop individuality Apparently identical ponds often have different pH and DO content at any given time Where should pond sampling take place? - CORRECT ANSWER- Same location every time 8 ft from water's edge 1 ft below surface Typical organic loading in a pond - CORRECT ANSWER- 10 - 50 lbs BOD/day/acre What are some ways of polishing pond effluent? - CORRECT ANSWER- Duckweed Land treatment Constructed wetlands Straw Ideal velocity for sanitary sewer collection systems - CORRECT ANSWER- 2 ft/sec Typical distance between manholes - CORRECT ANSWER- 300 - 500 ft

Purpose of preliminary treatment processes - CORRECT ANSWER- Remove course material from wastewater Purpose of primary treatment processes - CORRECT ANSWER- Remove settleable and floatable materials Purpose of secondary treatment processes - CORRECT ANSWER- Remove suspended and dissolved solids Sulfur dioxide (SO2) is used for... - CORRECT ANSWER- Used to neutralize chlorine & detoxify the effluent Ideal flow-through velocity of a grit channel - CORRECT ANSWER- 0.7-1.4 ft/sec 1 ft/sec is best Types of flow measuring devices in an open channel - CORRECT ANSWER- Parshall Flume & V-notch weir Types of flow measuring devices in a closed channel - CORRECT ANSWER- Venturi meter & magnetic flowmeter Advantages of measuring flow with a Parshall flume - CORRECT ANSWER- Smooth constriction no protruding edges waste will not collect behind the metering device

Ideal detention time in a primary clarifier - CORRECT ANSWER- 1.5-2 hrs Humus - CORRECT ANSWER- Layer of organisms (aka biomass) on trickling filter media that eventually gets thick enough to slough off and must be removed by settling in the secondary clarifier Typical BOD & suspended solids removal rate of an activated sludge plant - CORRECT ANSWER- 90 - 99% removal Mixed liquor - CORRECT ANSWER- Activated sludge + raw wastewater + return sludge in an aeration tank Types of bacteria present in a digester - CORRECT ANSWER- Acid formers & gas formers Typical organic matter removal rate of a digester - CORRECT ANSWER- 50% removal If temperature is kept at 95F, what is the typical digestion time in a digester? - CORRECT ANSWER- 30 days Byproducts of digestion - CORRECT ANSWER- Organic acids carbon dioxide gas methane

Typical gas ratio in a digester - CORRECT ANSWER- 70% methane, 30% CO Types of dewatering methods - CORRECT ANSWER- sludge drying beds lagoons centrifuges vacuum filters filter presses Shallow pond - CORRECT ANSWER- Aerobic 3 - 6 ft deep Oxygen throughout their depth Deep pond - CORRECT ANSWER- Anaerobic 8 - 12 ft deep Treatment depends on fermentation of sludge at the bottom Odorous Mainly for industrial waste Facultative pond - CORRECT ANSWER- Most common type of pond Top layer is aerobic Bottom layer is anaerobic Algae supplies oxygen to supernatant

Short-circuiting - CORRECT ANSWER- When flowing water entering a tank or basin flows along a nearly direct pathway from inlet to outlet, resulting in shorter contact or settling times Bar Racks - CORRECT ANSWER- Spacing between bars is 3-4 in Usually found in bypass channels Manually cleaned Bar Screens - CORRECT ANSWER- Spacing between bars is 3/8-2 in The more debris that collects on bar screens leads to... - CORRECT ANSWER- Greater head loss through bar screens Organic wastes settled out Dissolved oxygen is depleted Septic conditions Shear pin - CORRECT ANSWER- A straight pin that will break when a certain load or stress is exceeded Typical limit of allowable head loss at a bar screen - CORRECT ANSWER- 3 in of head loss Benefits of a communitor - CORRECT ANSWER- Reduction in screenings disposal Reduction in flies Reduction in odors

Most grit channels are designed to remove... - CORRECT ANSWER- 0.2 mm size sand & and all other heavier materials Typical settling rate of sand (0.2 mm) - CORRECT ANSWER- 0.075 ft/sec Settling time (sec) = - CORRECT ANSWER- Depth (ft) / Settling Rate (ft/sec) Grit channel length (ft) = - CORRECT ANSWER- [Depth of channel (ft) x Flow velocity (ft/sec)] / Settling Rate (ft/sec) If inspection of grit reveals a high amount of organic material... - CORRECT ANSWER- Velocity in the grit channel may be too low If inspection of grit reveals mainly large or heavy sand... - CORRECT ANSWER- Velocity in the channel may be too high Aerated grit chambers work on the basis of... - CORRECT ANSWER- Air and water have a lower specific gravity than water, so grit settles out better What is a slurry? - CORRECT ANSWER- A watery mixture or suspension of insoluble matter How does a cyclone grit separator work? - CORRECT ANSWER- Water and suspended particles are carried upward in the secondary vortex while heavy particles move outward and down in the primary vortex.

Typical grit quantities per volume wastewater - CORRECT ANSWER- 1 - 4 cubic ft / 1 MG When disposing of grit by burial, how much soil should cover the grit? - CORRECT ANSWER- 6 in What are the benefits of pre-aerating wastewater before grit removal? - CORRECT ANSWER- Improve grit removal efficiency Freshen wastewater Remove gases Add oxygen Promote flotation of grease Aid coagulation Primary sludges are usually ______ than secondary sludges - CORRECT ANSWER- Denser Types of sludge handling and disposal - CORRECT ANSWER- Sludge digestion Vacuum filtration Filter presses Incineration Land disposal Lagoons Burial

Surface Loading (GPD/sq ft) = - CORRECT ANSWER- Flow (gal/day) / Surface Area (sq ft) Detention time (hr) = - CORRECT ANSWER- [Tank Volume (cu ft) x 7.48 gal/cu ft x 24 hr/day] / Flow (gal/day) Recommended analyses for a primary clarifier - CORRECT ANSWER- Settleable solids Suspended solids BOD DO (effluent only) pH Temperature (influent only) Ideal velocity in a primary clarifier - CORRECT ANSWER- 1.0-2.0 ft/min Factors that influence settling characteristics in a primary clarifier - CORRECT ANSWER- Temperature Short circuits Detention time Weir overflow rate Surface loading rate Solids loading

What is the importance of knowing the weir overflow rate in a clarifier? - CORRECT ANSWER- To prevent short circuits or high velocity near the weir, which might pull settling solids into the effluent Weir Overflow Rate (GPD/ft) = - CORRECT ANSWER- Flow (GPD) / Length of Weir (ft) Recommended weir overflow rate for a primary clarifier - CORRECT ANSWER- 10,000-20,000 GPD/linear ft of weir Recommended surface loading rate in a clarifier - CORRECT ANSWER- 300 - 1200 GPD/sq ft Solids loading (lbs/day/sq ft) = - CORRECT ANSWER- [Flow (MGD) x MLSS (mg/L) x 8.34 lbs/gal] / Surface Area (sq ft) Typical solids loading in a secondary clarifier - CORRECT ANSWER- 12 - 30 lbs/day/sq ft Rationale for secondary clarifiers - CORRECT ANSWER- Biological treatment processes convert additional solids to the settleable form and also produce floc containing microorganisms The sludge volume in the secondary tank will be _____ from the activated sludge process than from the trickling filter process - CORRECT ANSWER- Greater Typical detention time for a secondary clarifier - CORRECT ANSWER- 2 - 3 hrs

Typical weir overflow rate for a secondary clarifier - CORRECT ANSWER- 5000 - 15000 GPD/lineal ft Typical return sludge rates at an activated sludge plant - CORRECT ANSWER- 10 - 50% of plant inflow Recommended analyses for a secondary clarifier - CORRECT ANSWER- Suspended solids Turbidity DO pH BOD Ammonia Nitrogen Sludge levels What is a sedimentation-digestion unit? - CORRECT ANSWER- A type of package treatment plant which combines a small clarifier over a sludge digester Chemical added to wastewater to raise the pH in a digester - CORRECT ANSWER- Lime or anhydrous ammonia In a sedimentation-digestion unit, how often should you remove supernatant? - CORRECT ANSWER- Twice a day for 15-30 min

In a sedimentation-digestion unit, how often should you remove sludge? - CORRECT ANSWER- Start wasting when solids start to appear in the supernatant Stop wasting when sludge starts to run thin What type of dewatering process is typical for a sedimentation-digestion unit? - CORRECT ANSWER- Sand drying beds Ideal temperature range for a digester - CORRECT ANSWER- 80 - 95 degrees F Recommended analyses for a sedimentation-digestion unit - CORRECT ANSWER- Inflow Suspended solids Settleable solids BOD (optional) Temperature pH Quantity of sludge withdrawn Chlorine residual (effluent) What is an Imhoff tank? - CORRECT ANSWER- A conical tank that combines sedimentation and digestion in the same unit Typical detention time in a septic tank - CORRECT ANSWER- 12 - 24 hrs What are colloids? - CORRECT ANSWER- Small, finely divided solids that remain dispersed in a liquid for a long time due to their size and electrical charge

Describe nitrification - CORRECT ANSWER- An aerobic process Bacteria oxidize ammonia and organic nitrogen in wastewater into nitrate First stage BOD is called carbonaceous BOD Second stage BOD is called nitrogenous BOD Describe denitrification - CORRECT ANSWER- Anoxic biological reduction of nitrate/nitrate nitrogen to nitrogen gas Nitrogen bubbles attach to the floc and float Common cause of rising sludge in secondary clarifiers What is ponding? - CORRECT ANSWER- A condition occurring on trickling filters When hollow spaces become plugged Water is unable to pass through the filter media Result of excessive slime growth, trash, or media breakdown Typical suspended solids and BOD removal efficiency of secondary treatment - CORRECT ANSWER- 90% or more List the components of a trickling filter - CORRECT ANSWER- Media Underdrain system Distribution system Typical size of rock media in a trickling filter - CORRECT ANSWER- 2 - 4 in wide Uniform in size

3 - 8 ft deep Void space is 35% of filter media Typical size of synthetic media in a trickling filter - CORRECT ANSWER- 15 - 30 ft deep Void space is 95% of filter volume Advantages of recirculation in a trickling filter - CORRECT ANSWER- Increased efficiency Dilutes strength of wastewater Prevents excessive buildup of slime growths Helps seed lower portions of filter with active organisms Helps keep biofilm healthy during low flow Addition of DO Controls flies Advantage of synthetic media - CORRECT ANSWER- Considerably more surface area per unit of dead space for slime to accumulate What effect does warm temperature have on a trickling filter? - CORRECT ANSWER- Organisms are more active Higher loadings Greater efficiency is possible What is hydraulic loading? - CORRECT ANSWER- The total volume of liquid (including recirculation) applied to a filter

Expressed as GPD/sq ft What is organic loading? - CORRECT ANSWER- The weight of BOD applied per day per 1000 cubic feet of filter media Expressed as lbs BOD/day/1000 cu ft Typical hydraulic loading of a standard-rate trickling filter - CORRECT ANSWER- 25 - 100 GPD/sq ft Typical organic loading of a standard-rate trickling filter - CORRECT ANSWER- 5 - 25 lbs BOD/day/1000 cu ft What is a roughing filter? - CORRECT ANSWER- A high-rate trickling filter that receives a very high organic loading (100-300 lbs/day/1000 cu ft) What should you check before starting a trickling filter? - CORRECT ANSWER- Replace packing grease of filter bearings Correct oil is used Distributor arms are level No foreign objects in fixed-spray nozzles No debris in underdrain system Valves operate smoothly Why should you record the speed of rotation of a trickling filter distributor arm during initial start-up? - CORRECT ANSWER- The distributor arm speed is proportional to the influent flow rate

Provides a reference for daily inspection and operation of distributor arm Typical time for slime to build up on trickling filter media - CORRECT ANSWER- Several days for slime growth to start Several weeks for fully developed slime How can you speed up the development of slime growth on a trickling filter? - CORRECT ANSWER- Recirculate wastewater prior to treating the main wastewater flow stream Add waste activated sludge Recommended daily observations in a trickling filter plant - CORRECT ANSWER- Indications of ponding Filter flies Odors Plugged orifices Roughness/vibration of distributor arms Leakage past the distributor turntable seal Splash beyond filter media Cleanup of slimes not on media Where should recirculation take place at a trickling filter plant and why? - CORRECT ANSWER- Primary clarifier Adds oxygen to incoming waste-stream Prevents odors

Recommended analyses for a trickling filter - CORRECT ANSWER- DO (final effluent & filter underflow) Settleable solids pH Temperature BOD Suspended solids Chlorine residual (final effluent) Coliform bacteria (final effluent) Clarity (final effluent) Advantage of performing COD analyses over BOD analyses - CORRECT ANSWER- 4 hrs to obtain results vs 5 days Nutrient requirements of a trickling filter - CORRECT ANSWER- For each incoming 100 lbs of BOD, there should be 5 lbs of ammonia nitrogen and 1 lb of orthophosphate Advantages of a trickling filter - CORRECT ANSWER- Less operating attention Shock loads are less frequent because recovery is faster Operational challenges of using a trickling filter - CORRECT ANSWER- Ponding Odors Flies Freezing

Major operational consideration/strategy at a trickling filter plant - CORRECT ANSWER- Use the lowest possible recirculation rate that will produce good results Operational criteria for a trickling filter plant - CORRECT ANSWER- Hydraulic loading rate Organic loading rate Recommended DO concentration of trickling filter effluent - CORRECT ANSWER- 3 - 6 mg/L (rock) 4 - 8 mg/L (synthetic) Operational strategies for making adjustments at a trickling filter plant - CORRECT ANSWER- Change in recirculation rate Change in staging (parallel vs series) Causes of ponding in a trickling filter - CORRECT ANSWER- Poor primary clarification Media is too small or not uniform Uncontrolled sloughing Accumulation of debris Growth of insects and snails on the media Purpose of running a two-stage filter plant in parallel - CORRECT ANSWER- To compensate for cold weather Influent waste is usually warmer than recirculated waste

Strategies for controlling abnormal flow at a trickling filter plant - CORRECT ANSWER- Increase the number of filters in operation Reduce recirculation rates Operate filters in parallel Two principal components of a centrifugal pump - CORRECT ANSWER- Impeller Pump casing Centrifugal pumps convert velocity head to ____ by a change of shape within the volute - CORRECT ANSWER- Pressure head Pump dry wells are now classified as... - CORRECT ANSWER- Confined spaces Centrifugal pumps are also classified as... - CORRECT ANSWER- Radial-flow Mixed-flow Axial-flow The majority of centrifugal pumps in the water industry are ____ pumps - CORRECT ANSWER- non-priming If packing is provided for a pump, it is usually lubricated with... - CORRECT ANSWER- Grease or clean water Mechanical seals are used to replace... - CORRECT ANSWER- Packing material

What is a hydraulic grade line? - CORRECT ANSWER- A line connecting points to which liquid would rise at various places along a pipe if piezometer tubes were inserted into the liquid Cavitation is what type of problem? - CORRECT ANSWER- A system problem With centrifugal pumps, as pump discharge rate increases... - CORRECT ANSWER- Head and pressure decrease What is shutoff head? - CORRECT ANSWER- The amount of pressure required to reach a condition where the flow rate in a vertical pipe connected to the operating pump becomes zero What is the maximum suction lift achievable by a centrifugal pump? - CORRECT ANSWER- 15 - 20 ft Rate at which water should escape from a packing gland to maintain proper lubrication levels - CORRECT ANSWER- 60 drops per minute Describe a pump's basic mechanics - CORRECT ANSWER- A device that adds energy to a liquid in order to move it from one point to another The entrance to a pump is called... - CORRECT ANSWER- Suction port What is pressure head? - CORRECT ANSWER- The height to which a liquid can be raised by a given pressure

What does the Hazen-Williams equation relate? - CORRECT ANSWER- Flow of water vs physical properties of a pipe Pressure drop caused by friction What is net positive suction head - CORRECT ANSWER- The pressure under which a liquid must enter the eye of the impeller to meet conditions defined by the pump curve How do you change the direction of current in a 3-phase induction motor? - CORRECT ANSWER- Reverse any two line leads connected to the motor How often should distributor arms on a trickling filter be flushed? - CORRECT ANSWER- Weekly Typical dimensions of an RBC filter - CORRECT ANSWER- 12 ft diameter 25 ft long What percent of media is submerged in an RBC? - CORRECT ANSWER- 40% Typical rotation speed of an RBC - CORRECT ANSWER- 1.5 RPM What makes a RBC a simple process to operate? - CORRECT ANSWER- No recycling of effluent takes place Describe staging at an RBC plant - CORRECT ANSWER- 1 shaft, 4 stages, flow is parallel to shaft

4 shafts, 4 stages, flow is parallel to shaft 4 shafts, 4 stages, flow is perpendicular to shaft Typical plant flow for an RBC plant - CORRECT ANSWER- 5 MGD or less Typical BOD removal efficiency of an RBC plant - CORRECT ANSWER- 80 - 95% Advantages of an RBC over trickling filter plant - CORRECT ANSWER- Elimination of distributor arm problems Elimination of ponding Elimination of filter flies Reduced media sloughing Efficient use of media Lack of anaerobic conditions Limitations of an RBC plant - CORRECT ANSWER- Lack of flexibility due to the absence of recirculation More sensitive to industrial waste Typical time for biological slime to grow on an RBC - CORRECT ANSWER- 1 - 2 weeks Appearance of healthy slime on an RBC - CORRECT ANSWER- Uniform Shaggy Brown-to-gray No bare spots