Wastewater Treatment: Questions and Answers, Exams of Water and Wastewater Engineering

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2024-2025 Wastewater Class 2 Ohio ABC

Part 2. Questions and Correct Verified

Answers. Graded A

1 cu ft/sec is equal to ________. 30024 gph 500 gpm 0.72 mgd 0.65 mgd - ANSD 40 CFR Part 503 provides regulations and guidelines for managing _______________. industrial discharges laboratory testing wastewater residuals (biosolids) toxic pollutant discharge - ANSC 65 000 gal/day of sludge from a primary clarifier is pumped to a gravity thickener. If the solids content of the sludge is 4% and the surface area of the thickener is 850 sq ft, what is the solids loading rate of the thickener? Assume the weight of the sludge is 8.34 lbs/gal. 12lbs/day/sq ft 26 lbs/day/sq ft 3 lbs/day/sq ft

19 lbs/day/sq ft - ANSB A ____________ controller receives sensor output from the process variable and compares it to the setpoint or desired result then adjusts the system accordingly. manual feedforward compound feedback - ANSD A ____________ controller receives sensor output from the process variable and compares it to the setpoint or desired result then adjusts the system accordingly. - ANSFeedback A "dewatering beach is a component of a(n) ________. anaerobic digester centrifuge belt filter press aeration basin - ANSB A biotower is an alternative to what wastewater treatment process? high-purity oxygen tank activated sludge aeration basin rotating biological contactor trickling filter - ANSD

A centrifugal pump must acheive a flow rate of 550 gpm against a total dynamic head of 75 ft. What would be the water horsepower requirement for this pump, assuming that the liquid to be pumped has a specific gravity of 1.2? 10.8 whp 12.5 whp 15.3 whp 6.4 whp - ANSB A chlorine demand test shows the __________________________. amount of chlorine needed to kill all coliforms safe amount of chlorine to add without harming the receiving stream amount of chlorine needed to remove the chemical oxygen demand amount of chlorine needed to provide a specific residual after a given time - ANSD A confined space atmosphere contains a combustible gas. At what percentage of the Lower Explosive Limit (LEL) for that gas is the atmosphere considered "hazardous"? 19.5% 10% 15% 1% - ANSC A control system that uses information about the inputs to a process in order to prevent process errors is known as a ________________ controller.

manual compound feed forward feedback - ANSC A dirty filtrate coming from your pressure filter dewatering system indicates either too high a feed pressure or ___________. the feed sludge solids concentration is too low lime scales on the edges of your pressure plates torn/punctured filter media too little sludge being fed to the system - ANSC A flow of 3700 gpd of sludge is pumped to a 37 000 cu ft digester. The solids concentration of the sludge is 6% with a volatile solids concentration of 75%. If the digester reduces volatile solids by 55%, how many lbs/day volatile solids are destroyed per cu ft of digester capacity. Assume the sludge weights 8.34 lbs/gal. Round to the nearest hundreth. 0.06 lbs VS destroyed/cu ft 0.1 lbs VS destroyed/cu ft 0.02 lbs VS destroyed/cu ft 0.04 lbs VS destroyed/cu ft - ANSC A good way to measure the biological activity and aeration in your biological reactor is to use the ________________ test. SOUR

SS

TKN

VSS - ANSA

A limiting factor for digester loading is ___________. hydraulic detention time pathogen type pathogen content sludge color - ANSA A low solids content in the aeration basin is typically indicated by the presence of _________________. a brown, leathery foam a black color with a rotten egg odor floating sludge a white, fluffy foam - ANSD A pH drop in an aerobic digester can be caused by ______________. clogging of diffusers nitrification or CO2 buildup hydraulic overloading organic underloading - ANSB A pH drop in an aerobic digester can be caused by ______________.

organic underloading hydraulic overloading nitrification or CO2 buildup clogging of diffusers - ANSC A positive displacement pump should never be started ____________. with the discharge valve closed with the discharge valve open without being primed before relieving all pressure in the discharge pipe - ANSA A properly functioning heated anaerobic digester can have an alkalinity as high as ___________. 1000 mg/L 5000 mg/L 2500 mg/L 500 mg/L - ANSB A screen system that can be internally or externally fed influent is the ___________. rotary drum screen continuous conveyor screen catenary bar screen reciprocating rake bar screen - ANSA

A secondary clarifier is 75 ft in diameter and receives a combined RAS and primary effluent flow of 4.0 mgd. If the MLSS concentration is 2450 mg/L, what is the solids loading rate on the clarifier? 14 lb/d/ft 17 lb/d/ft 12 lb/d/ft 19 lb/d/ft2 - ANSD A sludge pump has a bore of 10 in (0.83 ft) and a stroke length of 3 in (0.25 ft). If the pump operates at 32 strokes/minute, how many gpm are pumped? Assume 100% efficiency and volume displacement. Density of the sludge is 7.48 gal/cu ft. 12 gpm 32 gpm 26 gpm 20 gpm - ANSB A total chlorine dosage of 6.9 mg/L is required for disinfection. If the effluent flow is 3.1 mil.gal/day and the hypochlorite used has 65% available chlorine, how many pounds /day of hypochlorite will be required? 158 lbs/day 512 lbs/day 274 lbs/day 395 lbs/day - ANSC

A trickling filter loaded at a rate of 64 kg BOD5/100 m3×d (40 lbs. BOD5/ 1000 ft3/day) would be considered a______________. intermediate rate filter roughing filters low rate filter high rate filter - ANSA A vertical column of fluid is also known as _________. friction factor viscosity level head density height - ANSC A viscous, jelly-like slime covering a trickling filter or RBC is known as a(n) _____________. anaerobic film population biological growth filter fouling - ANSC A visual indicator of a chlorine leak ______________. can be seen on the leak gauge can be produced by spraying water on the system is green or reddish brown deposits on metal

is the presence of white vapors near the floor - ANS A water-filled mechanical pump seal not only helps to prevent leaks, but also ___________. keeps the pump primed cools the material being pumped acts as a reserve water supply prevents pump shaft wear - ANSD Aerobic digesters not only digest sludge, but can also be used to _________________. disinfect the sludge ferment the sludge thicken the sludge filter the sludge - ANSC After a settleometer test you have a thin layer of clear supernatant over a poorly settling sludge and your SVI is greater than 150 mL/g. This condition is referred to as ________________. septic sludge ashing sludge bulking pin floc - ANSC

An aerated grit chamber must maintain a constant velocity of ___________ for proper operation. 1.2 m/s (4 ft/sec) 0.9 m/s (3 ft/sec) 0.3 m/s (1 ft/sec) 0.6 m/s (2 ft/sec) - ANSC An anaerobic digester is failing when __________. methane-former numbers decrease volatile acid concentration increases alkalinity of the sludge decreases all of the above - ANSD An ideal carbon to nitrogen ratio for composting sludge is _______________. 500: 1: 30: 1:30 - ANSC As part of the national pretreatment program (40 CFR Part 403), plants with a design flow of more than ____________ must develop an industrial waste pretreatment program. - ANS19 000 m3/d (5 mgd) At temperatures less than _______, the rate of volatile solids reduction drops so low that aerobic digestion processes are rendered ineffective.

20°C (68°F)

10°C (50°F)

40°C (104°F)

30°C (86°F) - ANSB

Auxiliary fuel requirements in a multiple hearth incinerator are lower for sludges with a high percentage of volatiles. The volatile content of a sludge may be maximized by: All of the above Removing sludge inorganics such as grit Avoiding the use of ferric chloride and lime in the dewatering process Not digesting the sludge - ANSA Bacteria associated with fixed film reactors can thrive in water with a pH as low as ________.

5.5 - ANSD Blowers can produce discharge temperatures in excess of ____________. 93°C (200°F) 75°C (167°F) 58°C (136°F)

45°C (113°F) - ANSA

C - ANS

Calcium hypochlorite contains ___________% available chlorine. 85 65 20 40 - ANSB Chlorine can be used to control filter flies in trickling filters. The chlorine residual recommended for filter fly control is _______. 0.1 to 0.3 mg/L 1 to 2 mg/L 500 to 600 mg/L 200 to 300 mg/L - ANSB Class "C" extinguishers are used for ___________. electrical fires wood fires metal fires gas fires - ANSA Coliform bacteria are ____________.

A) pathogens which cause hepatitis B) more resistant to chlorination than pathogenic bacteria C) pathogens which cause typhoid D) less resistant to chlorination than pathogenic bacteria - ANSB Dominance of flagellates in your mixed liquor indicate ________? low F:M, high SRT low F:M, low SRT high F:M, high SRT high F:M, low SRT - ANSD For a trickling filter, organic loading is typically expressed as _____________. kg BOD (lb BOD) mg BOD/d (oz BOD/d) kg BOD/100m2×d (lb BOD/1000 ft2/d) kg BOD/100m3×d (lb BOD/1000 ft3/d) - ANSD For an activated sludge nitrification process, how much alkalinity is required to oxidize 0.45 kg (1 lb) of ammonia 6.70 kg (14.77 lb) 4.65 kg (10.25 lb) 7.72 kg (10.01 lb)

3.2 kg (7.14 lb) - ANS3.2 kg (7.14 lb) Theoretically, 3.2 kg (7.14 lb) is required to oxidize 0.45 kg (1lb) of ammonia. If this loss of alkalinity is not compensated for during nitrification, the pH will drop and the process can fail. For efficient removal, phosphorus must be biologically converted to ______________. orthophosphate polyphosphorus metaphosphorus organic phosphate - ANSA For preventive maintenance of a comminutor, how often should the channel be drained and the unit cleaned? monthly weekly annually daily - ANSA From a meatpacking plant, food industry, or dairy you would expect to find all of the following pollutants EXCEPT _____________. fats, oils, and grease volatile organics wide variations in pH high BOD - ANSB

Heat exchangers are typically used in a wastewater treatment plant for _______________. warming cold influent dissolving powder polymer into solution warming the contents of small clarifiers in cold weather heating sludge for anaerobic digestion - ANSD How many pounds of polymer must be added to 30 gallons of water to make a 0.1% polymer solution? 0.50 lbs 1.50 lbs 0.25 lbs 1.0 lbs - ANSC Hydrogen sulfide is _______________. insoluble in water, corrosive, and toxic soluble in water, corrosive, and toxic soluble in water, non-corrosive, and nontoxic soluble in water, flammable, and nontoxic - ANSB If a good floc forms before contacting a gravity belt thickener but the slurry exiting the belt is very wet, the most likely cause is _________________. the rollers are not parallel the belt tension is too tight

all of the above the belt is dirty and clogged - ANSD If adding sodium bicarbonate to an anaerobic digester for pH control, care should be taken not to overdose because ___________________________. CO2 will be consumed and can result in a vacuum in the tank sodium toxicity can result calcium carbonate can precipitate and cause problems pH may spike above 12.0 - ANSB If it is determined you need to add chlorine to your RAS to control a filamentous problem, what is typically the maximum safest dosage used for this process? 10 - 15 kg of chlorine for every 1000 kg of MLVSS (10 lb chlorine for every 1000 lb MLVSS) 8 - 10 kg of chlorine for every 1000 kg of MLVSS (4lb chlorine for every 1000 lb MLVSS) 1 - 2 kg of chlorine for every 1000 kg of MLVSS (1lb chlorine for every 1000 lb MLVSS) 3 - 5 kg of chlorine for every 1000 kg of MLVSS (2lb chlorine for every 1000 lb MLVSS) - ANSD If solids in water have a specific gravity of 1.30, then they are _______________. 30 % heavier than water 3 % lighter than water 13 % heavier than water

30 % lighter than water - ANSA If the ammonia concentration in an anaerobic digester exceeds ____________, the environment becomes toxic. 3000 mg/L 1000 mg/L 5000 mg/L 200 mg/L - ANSA If there is a significant rise in the volatile acid to alkalinity ratio in your anaerobic digester, you should NOT _________________. increase the sludge withdrawal rate add seed sludge from a secondary digester or other solids process extend the mixing time adjust the digester temperature for an extended period of time - ANSA If your RAS rate is too high, what is typically the primary result? solids will overload the clarifier and wash out the solids level to the final effluent decreases aeration in the basin would increase anaerobic conditions would develop in your secondary clarifier - ANSA In order to control odor from hydrogen sulfide, wastewater containing sulfides should be maintained at a pH of ____________.

less than 7 about 7 about 9 less than 4 - ANSC In order to promote nitrification in an activated sludge process, the ____________ can be lowered. pH F:M ratio wastewater temperature RAS rate - ANSB In terms of mechanical equipment in a treatment plant, MCC stands for _________. main circuit conductor maintenance management center motor current control motor control center - ANSD In terms of sludge thickening (primarily gravity thickening), WAS typically can be described as __________. compacting easily has a low sludge volume index settling rapidly

forming a light, fluffy floc that settles poorly - ANSD In the contact stabilization process, where is the food absorbed into the process? clarifier reaeration reactor contact reactor influent - ANSC In the wastewater industry, PLC refers to a _______________________. Pressure Limit Control Programmable Logic Controller Plastic-Lined Conduit Pump Level Circuit - ANSB In the wastewater industry, PLC refers to a _______________________. Programmable Logic Controller Pump Level Circuit Pressure Limit Control Plastic-Lined Conduit - ANSA Jar tests indicate that the best liquid polymer dose for waste stream is 12 mg/L. The flow to be treated is 2.5 mil. gal/day. Determine the gpd setting for the liquid polymer chemical feeder if the liquid polymer is a 60% solution (assume the polymer solution weights 8.34 lb/gal). 1% equals 10,000 mg/L.

100 gpd 50 gpd 25 gpd 10 gpd - ANSB Mean cell residence time (MCRT) is mathematically described as the mass of solids (lb or kg) in a process _____________________. divided by the mass of solids leaving the process (lb/d or kg/d) multiplied by the amount of solids entering the system (lb/d or kg/d) divided by the concentration of solids in the system (mg/L) multiplied by the concentration of solids in the system (mg/L or ppm) - ANSA Most gas piping systems are rated for _____________service. 700 kPa (100 psi) 1050 kPa (150 psi) 1500 kPa (200 psi) 350 kPa (50 psi) - ANSB Muriatic acid is also known as _____________. ferric chloride sodium hydroxide hydrochloric acid sulfuric acid - ANSC

NPDES permits outline all of the following parameters EXCEPT _________________. plant safety requirements monitoring and reporting requirements discharge location allowable flows - ANSA Operators begin to note that the wastewater in the 2 primary sedimentation tanks occasionally looks black and has a strong odor. You look back through the operating logs and note the following: Influent flows through the plant have been fairly constant. poor quality (high BOD) centrate is being returned to the primary sedimentation tanks Poor quality (high BOD) digester supernatant is being returned to the primary sedimentation tanks. wastewater is going septic in the collection system intermittent industrial discharges such as inks and dyes are causing the sedimentation tank contents to appear black - ANSB Operators that may be required to wear SCBAs cannot ______________. grow beards have less than 100% lung capacity have any facial hair have recent dental work - ANSA ORP stands for __________.

a. Oxygen Recirculation Pump b. Oxygen Reclamation Process c. Oxygen Residual Probe d. Oxidation-Reduction Potential - ANSD Potassium permanganate is used for _______________. odor control stabilization coagulation disinfection - ANSA Potassium permanganate is used for _______________. stabilization disinfection coagulation odor control - ANSD Predominance of free-swimming cillates and flagellates in activated sludge indicate? Low F/M, High SRT High F/M, Low SRT High F/M, High SRT Low F/M, Low SRT - ANSB

Reasons for flow equalization include all of the following, EXCEPT _________________. temperature fluctuation control pH variation damping flow variation damping BOD load fluctuation control - ANSA Sludge cake is moved through a multiple-health furnace by a process called ______________. rabbling pushing dosing turning - ANSA Sludge depth should not be greater than ______________ on gravity drying beds. 5 to 10 cm (2 to 4 in) 46 to 51 cm (18 to 20 in) 20 to 30 cm (8 to 12 in) 30 to 38 cm (12 to 15 in) - ANSC Some pressure filter systems for dewatering use a __________ system to help dewater sludges high in oils and grease. vacuum heating

precoat compressed air - ANSC Steps used to control filter flies on your trickling filter include increased hydraulic loading, cleaning spray nozzles, occasionally flooding the filter, and __________. chlorinating the filter draining the filter for an extended period of time changing to a new type of media fumigating the filter and area with pesticides - ANSA Stuffing boxes are primarily used to keep _____________ out of pump shafts. oil electricity air horsepower - ANSC The adverse effect a substance has on a living entity defines that substance's _________________. acidity toxicity alkalinity demand - ANSB The best method for protecting a steel tank from rust is _____________.

maintaining interior humidity painting regular washing adding a protective coating - ANSD The desired solids loading rate for a 80-ft diameter clarifier is 40 lbs/day/ sq ft. If the flow to the clarifier is 6.5 MGD, what is the required MLSS concentration? 4615 mg/L 3707 mg/L 3517 mg/L 3920 mg/L - ANSB The desired solids loading rate for a 80-ft diameter clarifier is 40 lbs/day/ sq ft. If the flow to the clarifier is 6.5 MGD, what is the required MLSS concentration? 4615 mg/L 3707 mg/L 3517 mg/L 3920 mg/L - ANSB The destabilization of sludge particles by decreasing the repulsive forces between particles is called ____________. equilization flocculation coagulation