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Grade 4 wastewater 101 certification
practice test
What is the beneficial concentration range of magnesium in an anaerobic digester?
a. 50 to 100 mg/L b. 75 to 150 mg/L c. 100 to 200 mg/L d. 150 to 250 mg/L - โ โ c. 100 to 200 mg/L
If the supernatant from an anaerobic digester that is returning to the plant process is of poor quality and is causing plant upsets, what is the most probable cause?
a. organic overload has occurred b. a toxic load has entered the digester c. there is excessive mixing and settling time is insufficient d. sludge recirculation line is partially or completely plugged - โ โ c. there is excessive mixing and settling time is insufficient
If the odor of the supernatant is sour from either the primary or secondary anaerobic digester, what is the most probable cause?
a. digester being overheated b. recirculation of gas is excessive c. digester pH is too low d. volatile-acid-to-alkalinity ratio has increased to 0.8 - โ โ c. digester pH is too low
What is the most probable cause of foam in the supernatant from either the single stage or the primary tank?
a. digester too stagnant as mixing is inadequate b. filamentous organisms are dying off by the billions c. excessive gas recirculation d. digester being overheated - โ โ c. excessive gas recirculation
At what pH will sodium hydroxide control sulfide generation for periods of about a month or more?
a. 9.5 b. 10.5 c. 11.5 d. 12.5 - โ โ d. 12.
What is the recommended organic loading rate in lb BOD/d/yd3 of media for an odor removal tower?
a. 0.2 b. 0.5 c. 1.0 d. 1.4 - โ โ b. 0.
The best temperatures reported for combusting odorous gases from a wastewater plant begin at temperatures greater than
a. 1,000ยฐF b. 1,200ยฐF c. 1,500ยฐF d. 1,800ยฐF - โ โ c. 1,500ยฐF
How many times can activated carbon be regenerated before it is usually replaced?
a. 3 times b. 6 times c. 9 times d. 11 times - โ โ a. 3 times
a. an algae bloom b. suspended solids to float c. oxygen toxicity for protozoans and other organisms, especially rotifers d. the formation of pinpoint floc - โ โ d. the formation of pinpoint floc
In the oxidation ditch process, what should be done if dark solids appear in the settling tank?
a. increase disinfection to reduce septic conditions and waste b. increase the return sludge rate c. add oxygen to the settling tank through the clarifier's diffusers d. waste all the solids and start the settling process over - โ โ b. increase the return sludge rate
A thick dark foam on the surface of the oxidation ditch indicates that the
a. process is performing well b. rotor revolutions per minute (rpm) are too fast c. wasting rate should be increased d. flow through the ditch is too slow - โ โ c. wasting rate should be increased
What should the operator do if the oxidation ditch becomes hydraulically overloaded due to a heavy rainstorm?
a. temporarily store the excess rainwater in the primary clarifier b. increase the dissolved oxygen levels c. shut down one or more rotor assemblies d. send excess wastewater to the settling tank - โ โ c. shut down one or more rotor assemblies
The blower system at a wastewater plant has to be shut off for cleaning the activated sludge process. The process will not be adversely affected, if the system is off for only
a. 5 to 10 min b. 15 to 30 min c. 30 to 60 min d. 1 to 2 hr - โ โ c. 30 to 60 min
When the pressure difference indicated on a manometer reads _______, the air filters on a blower for an aeration tank should be cleaned or changed.
a. 3 in. b. 5 in. c. 7 in. d. 10 in. - โ โ a. 3 in.
The waste activated sludge wasting rate should not be changed by more than _______ from one day to the next.
a. 10 to 15% b. 20% c. 20 to 25% d. 25% - โ โ a. 10 to 15%
What is the possible number of pounds of sludge volatile matter produced per pound of biochemical oxygen demand (BOD) removed from a conventional plant running the activated sludge process?
a. 0.15 lb b. 0.25 lb c. 0.55 lb d. 0.85 lb - โ โ c. 0.55 lb
If an operator calculates the wasting rate for activated sludge to be 45 gpm over the following 24 hr, the operator should waste
a. bulking; septicity b. septicity; denitrification c. too high a flow; bulking d. too high a flow; septicity - โ โ b. septicity; denitrification
A settleability test is performed on a secondary clarifier at an activated sludge plant. If the sludge floats too soon, then the sludge age should be reduced. What else may be done?
a. increase the DO b. decrease the BOD c. increase the F/M (food-to- microorganism) ratio d. decrease the F/M ratio - โ โ c. increase the F/M (food-to-microorganism) ratio
If the mixed liquor suspended solids (MLSS) concentrations of one aeration tank are substantially different from another aeration tank at an activated sludge plant, what would be the most probable cause?
a. alkalinity too low in one of the tanks b. diffusers plugged or broken in one of the aeration tanks c. denitrification has occurred in one of the tanks d. aeration tanks have unequal flow distribution - โ โ d. aeration tanks have unequal flow distribution
What would be the most probable cause for the return sludge to have too low a sludge concentration?
a. the mean cell retention time is too short b. sludge is being overoxidized c. sludge is being underoxidized d. the sludge consists
mainly of actinomycetes - โ โ d. the sludge consists mainly of actinomycetes
If filamentous organisms are the cause of sludge floating on the surface of secondary clarifiers, what would be the best solution?
a. decrease DO in aeration tank b. increase sludge return rate c. reduce mean cell residence time (MCRT) d. decrease pH to 6.5 - โ โ b. increase sludge return rate
If a toxic shock load caused pin floc in the overflow of the secondary clarifier, what would be the best course of action?
a. increase the MCRT b. get the sludge return rate as high as possible c. decrease the sludge return rate as soon as possible d. decrease the DO in the aeration tank(s) - โ โ b. get the sludge return rate as high as possible
If the mean cell retention time was too long and caused dark tan foam on the aeration tank, what would be the best course of action?
a. moderately increase sludge wasting to reduce the MCRT b. quickly increase sludge wasting to reduce the MCRT c. slowly but significantly decrease sludge wasting to reduce the MCRT d. quickly decrease sludge wasting to reduce the MCRT - โ โ a. moderately increase sludge wasting to reduce the MCRT
a. stalked ciliates b. free-swimming ciliates c. rotifers d. Mastigophora - โ โ c. rotifers
If an activated sludge plant is not experiencing sludge bulking or high sludge volume index (SVI) problems, then there is no need to count
a. stalked ciliates b. free-swimming ciliates c. filaments d. large Mastigophora - โ โ c. filaments
When looking through a microscope, an operator sees the presence of nematodes and a predominance of rotifers from a sample collected from the activated sludge plant. What is the most likely cause?
a. DO is too low b. anaerobic conditions exist c. F/M ratio is too low d. MCRT is too short - โ โ c. F/M ratio is too low
If the activated sludge sample contains predominately nematodes and rotifers, then the activated sludge process most probably
a. has high F/M ratio and high MCRT b. has high F/M ratio and low MCRT c. has low F/M ratio and high MCRT d. has low F/M ratio and low MCRT - โ โ c. has low F/M ratio and high MCRT
In the step-feed and contact stabilization modes, what would most likely happen if the return activated sludge (RAS) flow was increased?
a. it would decrease the SVI b. it would increase the SVI c. reaeration detention time would be reduced d. it would decrease the F/M ratio - โ โ c. reaeration detention time would be reduced
Why does a sequencing batch reactor (SBR) usually produce a better effluent than a conventional activated sludge plant?
a. because only the top 50% of the supernatant is decanted b. because only the top 70% of the supernatant is decanted c. because the water is motionless just before it is decanted d. because the SBR concentrates the suspended solids more efficiently - โ โ c. because the water is motionless just before it is decanted
If a sequencing batch reactor normally removed BOD and suspended solids, what would an operator have to do to also remove nitrogen and phosphorus?
a. increase the mixing time b. increase the mixing and aeration time c. increase the reaction and settling time d. increase the aeration and settling time - โ โ c. increase the reaction and settling time
An operator starting up a new sequencing batch reactor plant obtains 2,000 gal of seed sludge from another activated sludge plant. How long will it take before this seed sludge is capable of treating wastewater?
a. 3 to 5 days b. 1 to 2 weeks c. 1 month d. 2 months - โ โ b. 1 to 2 weeks
a. 10 days b. 15 days c. 20 days d. 30 days - โ โ b. 15 days
In general, a wastewater activated sludge plant will lose activated sludge in the effluent at a rate of _______ of the total solids required to be wasted.
a. < 2.5% b. < 5% c. < 7.5% d. < 10% - โ โ b. < 5%
Respiration rate values for activated sludge of less than 4 mg O2/hr/gm MLSS indicates
a. typical values of most conventional activated sludge processes b. understabilized organic matter c. biological organisms are not healthy or stable d. organic matter is undergoing rapid biodegradation - โ โ c. biological organisms are not healthy or stable
Respiration rate values for activated sludge of more than 20 mg O2/hr/gm MLSS indicates
a. slow biodegradable organic matter b. typical values of most conventional activated sludge processes c. biological organisms are not healthy or stable d. organic matter is undergoing rapid biodegradation - โ โ d. organic matter is undergoing rapid biodegradation
Which one of the following is the most common cause of wastewater toxicity to microorganisms due to its excessive amounts?
a. heavy metals b. acids c. petroleum products d. detergents - โ โ d. detergents
Which one of the following is the least common cause of wastewater toxicity to microorganisms?
a. residual chlorine b. free ammonia c. chlorinated hydrocarbons d. solvents - โ โ c. chlorinated hydrocarbons
In the startup of an industrial waste treatment plant, chemicals are added to the aeration basin until the microorganisms reproduce and approach an MLSS level of
a. 2,000 mg/L b. 2,500 mg/L c. 3,000 mg/L d. 3,500 mg/L - โ โ a. 2,000 mg/L
What is the odor detection limit of chlorine gas?
a. 0.1 ppm b. 0.3 ppm c. 0.5 ppm d. 1.0 ppm - โ โ b. 0.3 ppm
What is a cathode?
a. negative pole of an electrolyte b. positive pole of an electrolyte c. negative pole of an electrolytic cell or system d. positive pole of an electrolytic cell or system - โ โ negative pole of an electrolytic cell or system
The least reactive metals are called a. anodic metals b. galvanic metals c. cathodic metals d. tempered metals - โ โ c. cathodic metals
a. a digester to destabilize and break down the toxins b. an approved sanitary landfill c. an incinerator d. a sludge pond for further aerobic breakdown - โ โ b. an approved sanitary landfill
Which one of the following best defines the term stray-current corrosion?
a. decomposition of a metal by its reaction with an acidic water b. decomposition of a material caused by an outside electric current c. reaction between a metal and water d. reaction between two different metals with water acting as an electrolyte - โ โ b. decomposition of a material caused by an outside electric current
On startup of a small package wastewater treatment plant, lime should be added to the digestion unit when the pH goes below
a. 6.8 b. 7.0 c. 7.2 d. 7.5 - โ โ b. 7.
If the effluent to a small package wastewater treatment plant using the activated sludge process appears turbid, what is most probably the cause?
a. low concentration of dissolved oxygen (DO) in the aeration tank b. pumping rate for the return of activated sludge is out of balance c. excessive aeration rates in the aeration tank d. alkalinity is too high - โ โ b. pumping rate for the return of activated sludge is out of balance
If a small package treatment plant utilizing the activated sludge process has a lightcolored floating sludge on the surface of the clarifier, which one of the following would most likely eliminate the floating sludge?
a. increase the sludge wasting rate b. add a pH stabilizer, as pH is too low c. reduce the aeration rates d. increase the return sludge rate - โ โ c. reduce the aeration rates
What usually causes frothing in the activated sludge process?
a. too low a solids level b. too high a solids leaving c. too short a retention time d. too long a detention time - โ โ d. too long a detention time
Which one of the following suggestions would most likely control foaming?
a. increase the detention time b. water sprays c. increase the dissolved oxygen d. increase solids wasting - โ โ b. water sprays
What is the ideal level of solids in a jar test sample collected from an aeration tank if it is allowed to settle for 30 min?
a. ยผ of the jar depth b. โ
of the jar depth c. โ
of the jar depth d. ยฝ of the jar depth - โ โ d. ยฝ of the jar depth
If a wastewater plant receives highly variable flows, it can store the wastewater during periods of high flow and release the wastewater during periods of low flow. What is the recommended storage volume in percent of total daily flow for such a wastewater plant?
a. 10 to 20% b. 25 to 33% c. 30 to 40% d. at least 50% - โ โ a. 10 to 20%
Why do petroleum waste treatment plants use the extended aeration mode?
a. to maximize petroleum waste degradation by oxidation b. to increase the mixed liquor volatile suspended solids (MLVSS) and thus maximize oxidation of petroleum wastes c. to maintain the nitrification population essential for ammonia oxidation d. to maintain a low F/M ratio, which causes the microorganisms to use sulfides as an energy source - โ โ c. to maintain the nitrification population essential for ammonia oxidation
What could be added to the effluent if phenols are close to the National Pollutant Discharge Elimination System (NPDES) limit at a petroleum waste plant?
a. soda ash b. caustic soda c. nitric acid d. hydrogen peroxide - โ โ d. hydrogen peroxide
What is the optimal pH range for the biological nitrification process?
a. 7.0 to 7.3 b. 7.3 to 7.9 c. 7.3 to 8.0 d. 7.5 to 8.5 - โ โ d. 7.5 to
What is the temperature range for good nitrification to take place?
a. 60 to 95ยฐF b. 70 to 80ยฐF c. 75 to 85ยฐF d. 75 to 95ยฐF - โ โ a. 60 to 95ยฐF
In the nitrification process, phosphorus is added to the aeration system and adjusted according to _______ and the concentration of total Kjedahl nitrogen (TKN) in the wastewater.
a. MLSS b. MLVSS c. BOD5 level d. MCRT - โ โ c. BOD5 level
Adequate amounts of nitrogen and phosphorous are especially lacking most often from which one of the following wastes?
a. industrial b. domestic c. fermentation industries d. food processing - โ โ d. food processing
When treating industrial wastes, for every 100 lb of incoming BOD there should be how many pounds of ammonia nitrogen?
a. 1 lb b. 5 lb c. 10 lb d. 12 lb - โ โ b. 5 lb
