Wastewater Treatment Plant Operations, Exams of Water and Wastewater Engineering

Download Wastewater Treatment Plant Operations and more Exams Water and Wastewater Engineering in PDF only on Docsity!

Wastewater Treatment Operator Certification Test 2

202 4/2025 With Correct Questions And Answers

What is the methane content in a properly operating anaerobic digester? a. 30 to 35% by volume b. 1 to 2% by volume c. 65 to 70% by volume d. 15 to 20 % by volume - ANSWER>> c What will the addition of chlorine gas do to the pH of wastewater? a. Moderately increase the pH b. pH will not be affected c. Significantly increase the pH d. Decrease the pH - ANSWER>> d What is the purpose of a Parshall flume? a. Measure turbidity b. Measure flowrate c. Measure settling rate d. Measure solids content - ANSWER>> b What is the typical removal efficiency of settleable solids in a primary clarifier?

a. 95 to 99% b. 40 to 60% C. 20 to 50% d. 10 to 15% - ANSWER>> a Which of the following is true about pumping scum from a primary clarifier? a. Pumping scum is less problematic during cold weather b. Scum rarely leads to plugged pipelines due to its viscous nature c. Scum causes more piping problems than other substances pumped at a wastewater treatment plant. d. Scum causes the least amount of piping problems among all the substances pumped at a wastewater treatment plant pumped at a wastewater treatment plant - ANSWER>> c What might cause thick billows of white sudsy foam in the aeration tank? a. MLSS is too high b. Temperature in the aeration tank is too low c. Old sludge d. MLSS is too low - ANSWER>> d What does the "M" in F/M ratio represent? a. MLSS in the aeration tank

b. The influent BOD loading rate into the aeration tank c. The mixed liquor volatile suspended solids in the aeration tank d. The mass of inorganic solids in the aeration tank - ANSWER>> c In general- how will warmer temperature affect the settling rate of solids in a clarifier? a. Decrease the settling rate b. Increase the settling rate c. Temperature will not affect the settling rate d. Worsens the settling rate - ANSWER>> b What could happen if the digester gas is mixed with air (85 TO 95% by volume)? a. Cause an explosion b. Improve efficiency of digestion c. The bacteria will become aerobic and increase VSR d. The digester becomes safer to operate due to less toxic gas in the system. - ANSWER>> a How will algae impact the chlorine demand in the pond effluent? a. Slightly decreases chlorine demand b. Does not affect chlorine demand c. Significantly decreases chlorine demand

d. Increases chlorine demand - ANSWER>> d Which of the following is true about a positive displacement pump? a. It is a type of centrifugal pump b. Suction valve should be closed when the pump is started c. It must never be started with the discharge valve closed d. Adds head to liquid using several impellers - ANSWER>> c What is true about the F/M ratio? a. MLVSS data is not required to determine the F/M ratio b. Volume of the secondary clarifier is not needed to determine the F/M ratio c. The amount of COD or BOD entering the aeration tank does not have to be known to calculate the F/M ratio d. The amount of organisms in the aeration tank is not needed to calculate the F /M ratio - ANSWER>> b Which of the following is one of the basic rules of laboratory work? a. Do not leave keys in equipment or vehicles at any time b. Patrol the facilities frequently and look for suspicious activity or behavior c. Never pipet hazardous material with your mouth even if the pi pet has been sterilized

d. Lock out and tag out relevant mechanical and electrical equipment before starting any maintenance activity - ANSWER>> c What is the recirculation ratio for a trickling filter? a. Qr/Q b. Q/Qr c. Q/ Qr+Q d. Qr+Q/Q - ANSWER>> a Which of the following is true about COD and BOD? a. They are direct measurements of the organic content in the influent b. They measure the inorganic content of the influent c. They represent the amount of filamentous bacteria in the influent d. They are indirect measurements of the organic content in the influent - ANSWER>> d What is the purpose of the grit channel? a. Remove dissolved and non-settleable organics b. Remove heavy inorganic wastes. c. To allow activated sludge to settle d. Remove substances that float and readily settle from the wastewater as part of primary treatment. - ANSWER>> b

Which of the following is true about the extended aeration process? a. Bugs get more food b. Wasting is not necessary c. It does not produce as much waste sludge as other processes. d. It is very different from the conventional activated sludge process - ANSWER>> c What is the correct formula for solids in raw wastewater? a. Non-volatile solids + Suspended solids = Total solids in the influent b. Dissolved solids + Settleable solids = Total suspended solids c. Colloids + dissolved solids = total suspended solids d. Non-settleable solids + Settleable solids = Total suspended solids. - ANSWER>> d What is "freeboard" in a waste stabilization pond? a. Operational depth of the pond b. Wooden inlet and outlet structures c. Wooden baffles d. Vertical distance from normal water surface to the top of the levee. - ANSWER>> d What is one of the requirements for a BOD test? a. The BOD bottle should be completely filled to the top.

b. The BOD bottles must be 100-mL in size c. Sample bottles should be incubated at 30 degrees Celsius d. Stoppers should not be installed on the bottles to ensure proper air flow to the samples - ANSWER>> a What should be scheduled every 3 months for a flamer arrester in an anaerobic digester? a. Replacement b. Maintenance c. Flow test d. Temperature test - ANSWER>> b What is common practice in an activated sludge process? a. Waste all activated sludge b. Sludge age of 14 days for conventional system c. Recirculate activated sludge d. limiting DO to increase microorganism population - ANSWER>> c Prior to entering a permit-required confined space what should you verify? a. A standby person should be at the entrance to the confined space. An additional person is not required b. A standby person should be within 30 feet of the confined space.

c. A standby person should be within 50 feet of the confined space. d. A standby person should be located outside the entrance to the confined space while another person should be within sight or call of the standby person. - ANSWER>> d What is a common way to determine the organic strength of wastes in the influent? a. Test for the biochemical oxygen demand b. Test for the biological oxygen demand c. Test for the volatile solids reduction d. Test for the carbon and hydrogen concentrations - ANSWER>> a What should you do if you are mildly exposed to chlorine gas? a. Breathe heavily to inhale clean air b. Cough to release chlorine from lungs c. Immediately evacuate the contaminated area- remain calm- keep warm- breathe lightly- and avoid coughing d. Keep your body as cool as possible - ANSWER>> c What are the main sources of domestic sewage in the collection system? a. Canals b. Surface flow c. Ocean outfall

d. Households and commercial establishments - ANSWER>> d Why is it important to maintain a horizontal weir in a clarifier? a. Prevent sludge bulking b. Prevent short-circuiting c. Prevent gasification d. Prevent excessive slime growth - ANSWER>> b What are mostly removed in the grit channel? a. Biomass b. Organics c. Dissolved solids d. Sand- eggshells- cinders- and heavier particulate matter - ANSWER>> d How often should an anaerobic digester be fed? a. Several times a day b. Once a day c. Twice a week

4. Five times per week - ANSWER>> a What is the health effect of carbon dioxide? a. Vomiting b. Migraine c. Can lead to asphyxiation

d. Rapid heart beat - ANSWER>> c Which of the following enters the headworks of a treatment plant? a. Effluent b. Supernatant c. WAS d. Influent - ANSWER>> d Which gas diminishes your sense of smell? a. Hydrogen b. Hydrogen sulfide c. Nitrogen d. Ethane - ANSWER>> b What type of microorganism can use nitrate as a source of oxygen? a. Aerobic bacteria b. Anaerobic bacteria c. Facultative bacteria d. Zoogleal - ANSWER>> c What is the equivalent of 1 mg/L? a. 1 ppb b. 10 ppm

c. 10 ppb d. 1 ppm - ANSWER>> d Select the most accurate statement about extended aeration. a. The bugs are retained in the aeration tank much shorter than the conventional activated sludge system b. Extended aeration produces the most waste sludge compared to other activated sludge processes c. An oxidation ditch is usually operated in extended aeration mode and is used for small flows d. Extended aeration is the least common type of package plant treatment process - ANSWER>> c What is equivalent to organic solids? a. Volatile solids b. Fixed solids c. Suspended d. Colloids - ANSWER>> a What should be done if a large amount of organic matter is found in the grit channel? a. Decrease the velocity of wastewater b. Inject sodium hydroxide at the headworks c. Raise the pH d. Increase the velocity of wastewater - ANSWER>> d

Which flowrate should you use to calculate the hydraulic loading to a trickling filter? a. Plant inflow b. Plant inflow minus recirculated flow c. Plant Inflow plus recirculated flow d. Recirculated flow - ANSWER>> c What is the difference between the sludge from a primary clarifier and secondary clarifier? a. Secondary sludge is denser than primary sludge b. Primary sludge is denser than secondary sludge c. Specific gravity of secondary sludge is larger than that of primary sludge d. Primary sludge has a smaller specific weight than secondary sludge - ANSWER>> b Which process includes a blower? a. Trickling filter b. Waste stabilization pond c. Chlorine contact tank d. Activated sludge - ANSWER>> d How does an activated sludge system remove waste from wastewater?

a. Physical treatment b. Chemical treatment c. Biological treatment d. Radiological treatment - ANSWER>> c Which of the following best describes pre-chlorination? a. Mainly used for disinfection and requires a large amount of chlorine residual in the wastewater at the chlorine contact chamber b. Addition of chlorine to wastewater at the entrance to the plant and used for odor control- BOD reduction- grease removal- and aid sedimentation c. Injected on a well-clarified effluent d. Describes a type of chlorination to address sludge bulking - ANSWER>> b When would you expect reduced algae population and less oxygen released into a pond? a. Fall and winter when the weather is cool and sunlight is reduced b. Summer when there is abundant sunlight c. Spring when the weather transitions from cool to warm d. When photosynthesis is very effective and at its peak - ANSWER>> a What is the first step of the lockout/tagout procedure?

a. Shut down the equipment if it is operating b. Operate the energy isolating device so that the equipment is isolated from its energy source c. Lockout the equipment with assigned lock or tag d. Notify all affected employees that a lockout or tagged system is going to be used and the reason why - ANSWER>> d What type of process is the activated sludge system? a. Anaerobic b. Anoxic c. Aerobic d. Jonie - ANSWER>> c What will happen if too much raw sludge is added to the digester? a. pH will increase due to increase in sodium hydroxide b. Acid fermenters will predominate and lower the pH c. pH will not be affected d. Methane fermenters will thrive - ANSWER>> b What might cause sludge to rise in a clarifier? a. Gasification from aging sludge b. pH is too high c. Sludge withdrawal rate is too high d. Photosynthesis - ANSWER>> a

What happens when carbon dioxide is removed from a pond? a. Decreases pH b. pH is not affected c. Increases pH d. Sudden increase in H2S - ANSWER>> c How much dissolved oxygen should be in a conventional activated sludge system if good effluent is being produced? a. 6 to 8 mg/L b. 0.5 to 1 mg/L c. 4 to 6 mg/L d. 2 to 4 mg/L - ANSWER>> d What is the typical concentration of mixed liquor suspended solids in a conventional activated sludge process? a. 50 to 1000 mg/L b. 1000 to 4500 mg/L c. 4500 to 5500 mg/L d. 5500 to 6500 mg/L - ANSWER>> b The temperature of the plant influent is: a. Slightly warmer than tap water b. Slightly cooler than tap water c. Much cooler than tap water

d. Much warmer than tap water - ANSWER>> a The purpose of disinfection is to: a. Kill all microorganisms in the wastewater b. Stabilize the pH c. Destruction or inactivation of pathogenic bacteria d. Oxidize the minerals in the effluent - ANSWER>> c What must you do before entering a room with harmful concentration of chlorine gas in the air? a. Read the O&M manual b. Wear self-contained breathing apparatus (SCBA) c. Prepare the fire extinguishers d. Cover your mouth and spray aqueous ammonia in the room - ANSWER>> b What does black sludge at the bottom of a secondary clarifier located downstream of a trickling filter signify? a. Pumping rate is excessive b. Pumping duration is too long c. Detention time is too short d. Sludge has stayed in the secondary clarifier too long - ANSWER>> d

If the lab results show that the plant influent sample has a COD of 100 mg/Land a BOD of 300 mg/l- which of the following is most likely true? a. Lab results appear incorrect b. Carbon concentration is very high c. Organic content is unusually high d. COD seems excessive - ANSWER>> a If a primary clarifier is placed out-of-service then how should a plant with at least two trickling filters operate the system? a. Operate the filters in parallel b. Divert the influent to several trickling filters c. Operate the filters in series d. Maintain existing operation without changing filter arrangement - ANSWER>> c What is the main reason for preventing a direct connection between a potable water pipe and a stuffing box (packings) of a wastewater pump? a. Wears out the glands quicker b. Glands should not be wet c. Potable water will rapidly destroy the stuffing box d. Cross connection - ANSWER>> d Which of the following is true about algae in a pond?

a. During the daytime the algae will release carbon dioxide b. During the daytime the algae will release oxygen for the aerobic bacteria in the pond c. Algae uses sunlight to produce hydrogen sulfide d. Photosynthesis helps algae create carbon monoxide - ANSWER>> b Which of the following is not true about hydrogen sulfide? a. Hydrogen sulfide is flammable b. Hydrogen sulfide is explosive under certain conditions c. Hydrogen sulfide is lighter than air d. Hydrogen sulfide is toxic - ANSWER>> c What type of treatment is primarily used to thicken sludge instead of dewater the sludge? a. DAF b. Sludge drying bed c. Centrifuge d. Vacuum filters - ANSWER>> a Why should sludge at the bottom of a clarifier be removed in a timely manner? a. To improve the performance of the grit channel b. To maintain a consistent volume of sludge in the drying bed c. To minimize the formation of chloramines

d. To prevent sludge gasification which causes the sludge to float - ANSWER>> d What is the purpose of sludge digestion? a. Convert primary and secondary sludge to mostly hydrogen sulfide b. Increase efficiency of the OAF c. Reduce the volume of the sludge and stabilize the solids d. Increase solids volume - ANSWER>> c Which of the following is true about trickling filters? a. It is mostly an anaerobic process b. The three main parts of a trickling filter are media distribution system and underdrain c. In computing BOD loading it is standard practice to include the BOD of the re-circulated effluent d. Filter ponding is usually due to inadequate organic loading - ANSWER>> b Which of the following could cause foaming in an anaerobic digester? a. Temperature is kept constant b. Feeding sludge at regular short interval c. Digester is well-mixed d. Organic overload - ANSWER>> d

Which of the following parameters should be monitored several times a week in a pond? a. TDS b. MLSS c. Dissolved oxygen- temperature- and pH d. MLVSS - ANSWER>> c Which is true about the temperature in an anaerobic digester? a. Temperature in a digester should not be changed by more than 1 degree Fahrenheit per day b. Temperature must be changed significantly according to sludge loading rate c. Temperature at the bottom should be higher than at the top of the digester d. Mesophilic digestion requires a temperature between 105 to 108 degrees Fahrenheit - ANSWER>> a The effectiveness of disinfection is determined by: a. The chlorine residual concentration b. The chlorine demand c. The chloramine concentration in the effluent d. The coliform concentration in the effluent - ANSWER>> d

An increase in the acid/alkalinity ratio for an anaerobic digester means: a. The digester ls in an ideal condition b. The carbon dioxide content is decreasing c. Acid concentration is increasing or alkalinity is decreasing d. pH of the sludge in the digester is increasing - ANSWER>> c Which of the following will not cause short-circuiting in a clarifier? a. Uneven weir settings b. Flow line of launder is low c. Damaged or missing inlet line baffles d. Velocity of wastewater is greater in some sections than in others - ANSWER>> b A grab sample is most suited for these constituents. a. BOD b. TSS c. Suspended solids concentration d. Residual chlorine - ANSWER>> d The organic loading to a trickling filter is expressed as: a. lbs BOD/day/1000 ft3 b. lbs BOD/day/1000 ft2 c. lbs BOD/day/ft2

d. lbs BOD/1000 gallon - ANSWER>> a How often should the sludge at the bottom of a clarifier be pumped? a. Once a week b. Bi-weekly c. Frequently throughout the day d. Once every three days - ANSWER>> c Which of the following will not affect settling characteristics in a clarifier? a. Temperature b. Short circuit c. Detention time d. Depth of launder - ANSWER>> d The best way to evaluate the effluent TSS concentration from a plant is to: a. Check the grab sample at peak flow b. Check the composite sample of TSS c. Check the grab sample at low flow d. Check the grab sample during average flow - ANSWER>> b Which of the following is not associated with an aeration tank? a. RAS

b. WAS c. RBC d. MCRT - ANSWER>> c What creates hydrogen sulfide? a. Excessive aeration b. Surface active agents c. Organic matter under aerobic condition d. Decomposing organic matter under anaerobic condition - ANSWER>> d A pond with a detention time of less than three days will perform similar to: a. Sedimentation tank b. Aeration tank c. Trickling filter d. RBC - ANSWER>> a Which type of bacteria is used for a trickling filter? a. Anaerobic bacteria b. Anoxic bacteria c. Aerobic bacteria d. Facultative bacteria - ANSWER>> c Which of the following is not associated with a trickling filter?

a. Media b. Filamentous bacteria c. Zoogleal film d. Recirculation - ANSWER>> b What is an MCRT? a. A calculation that indicates the tendency of activated sludge solids to thicken b. A measure of food provided to bacteria in an aeration tank c. The amount of volatile suspended solids in the mixed liquor- of an aeration tank d. An expression of the average time a microorganism will spend in an activated sludge process - ANSWER>> d What is the typical BOD removal efficiency in a primary clarifier? a. 10 to 15% b. 40to 60% c. 20 to 50% d. 95 to 99% - ANSWER>> c What does the "F" in F/M ratio represent? a. The microorganism population in the aeration tank b. The amount of filamentous bacteria in the activated sludge process c. The MLVSS in the aeration tank

d. The food for the microorganisms flowing into the aeration tank in lbs/day - ANSWER>> d Which of the following describes the appearance of healthy activated sludge? a. Thick greasy dark tan foam b. Brown with a moderate amount of crisp white foam c. Clear liquid with clear foam d. Gray liquid with no foam - ANSWER>> b What is used to control filamentous organisms? a. Polymer b. Sulfur dioxide c. Coagulant d. Chlorine - ANSWER>> d What are commonly used to control chlorine feed rate for disinfection? a. BOD and MLVSS b. pH and temperature c. Flow and chlorine residual d. DO and TSS - ANSWER>> c Which toxic gas is commonly found in septic wastewater and smells like rotten eggs?