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91 Cards in this Set

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What are the three types of anaerobic digesters?
psychrophilic, mesophilic, thermophilic
What is the temperature range in psychrphilic digester?
50 - 67 ° F
What is the temperature range in mesophilic digester?
68-113 °F
What is the temperature range in thermophilic digester?
114-135 °F
the operating temperature should never vary ( go up or down) more then how many degrees per day?
plus or minus 1 °F
What are the 2 stages in an anaerobic digester??
acid forming and gas (methane) forming
What stage is more sensitive to changes in temperature or digester environment?
gas formers
What is the purpose of a secondary digester?
storage prior to dewater and to provide seed sludge when the digeter is upset, stuck or sour
What is the best way to feed a digester?
small amt, continuously
Why shouldn't supernatant be withdrawn from the primary digester?
a. because you may remove gas formers with the supernatant
a. because the primary digester is completely mixed
what parameter is considered the best to use to monitor an anaerobic digester?
volatile acid to alkalinity ratio
what is the ideal VA/A ratio?
0.1
If the VA/A ratio go up, what action is needed?
stop feeding; feeding sludge from secondary digester; or add alkalinity
how much gas is produced for every cu ft volatile matter destroyed?
8 to 12 cu ft of gas
what is acid regression?
acid production is reduced and ammonia compounds form. pH goes up
the capacity of water to neutralize acids is called?
alkalinity
what is the decant liquid or supernatant taken form the centrufuge called?
centrate
rapid withdrawal of thickened sludge causes what condition?
coning
the washing of digested sludge is called
elutriation
during which stage to microorganisms oxidize their own cellular mass?
endogenous
What is an lysimeter?
a device used to measure the water draining though the soil
What is possitive pressure?
PSI greater then atmospheric
What is negative pressure?
PSI less then atmospheric
which microorganism lives on dead or decaying matter and is an acid former?
saprophytes
What is struvite?
scale or deposit of magnesium ammonium phosphate hexahydrate
When is the best time to remove supernatant?
during low flows to the plant
What is the best way to avoid foaming problems in the digesters?
start mixing as soon as you start filling the digester
What is the common microorganism found in anaerobic digestion?
facultative
how do microorganisms get oxygen in an anaerobic digester?
from molecular oxygen in compounds of PO4,NO2,SO4,NO3 etc
What is purpose of a flame arrester?
prevents flame or spark from entering digester
what is the purpose of thermal valve?
when fusible elements melts it shuts off flow of gas
when should flame arresters be serviced?
once a quarter
What keeps the floating cover from falling into the tank?
corbels
what keeps the floating cover level?
ballast
what keeps the floating cover from falling in the digester sludge?
the floatation chamber
the floating cover is tilted, there is no scum visible around the edges. What is likely cause?
a. ballast broken off
a. rain water collection on the top of cover
a. water in floating cover chamber
floating cover tilting. There is heavy scum around the edges. What is the likely cause?
scum blanket
how are samples taken from an anaeroic digester?
thief hole
What should the mixture of gas be?
30% CO2 and 70% methane
What is the indication that there is too much caron dioxide?
yellow flame
how often should you clean an anaeroic digester?
3-8 years
what condition indicates the digester needs cleaning?
when 1/3 of capacity is filled or process failing
what color is the supernatant?
amber ( really usually grayish)
what color is the digested sludge?
black
how are digesters heated?
heat exchangers
What is used to mix digesters?
mixers, draft tues, recirculation, and gas
What is used to measure pressure?
manometers
The scum blanket causes what problems?
keeps bugs from food
What is purpose of floating covers?
provides flexile space for gas storage
Supernatant from anaerobic digester was returned to headworks. The MLSS is good but the effluent is turbid. What is likely cause?
the MLVSS is low
what percentage of gas formation should take place in primary digester?
90%
Anaerobic supernatant is returned to the AT. the MLSS remains good, but the effluent deteriorates. What is the likely cause?
a. low WAS & high SVI
b. MLVSS decreased
c. low aeration
pH increased
a. low WAS & high SVI
Acidity is the measure of the _______?
a.Acid strength of a liquid
b.hydroxide cont
c. capacity to buffer against acids
d. both A & C
a.Acid strength of a liquid
In the anaerobic digester, which stage is the most sensitive to changes in loading, pH and temperature?
a. acid forming
b.methane forming
c. supernatant withdrawal
d. sludge withdrawal
b.methane forming
If scum layer is formed in an anaerobic digester, what can happen?
a.overproduction of methane
b. coning
c. food entrapment preventing bug contact
d. increased supernatant
c. food entrapment preventing bug contact
When is the best time to withdraw supernatant for a digester?
a. when gas formation is slow
b. during high flows
c. during low flows
d. when coning occurs
c. during low flows
operators should avoid withdrawing supernatant from a primary digester because?
a. high temp
b. coning
c. gas formers may be removed
d. clogging of thief hole
c. gas formers may be removed
rapid withdrawal of digested sludge can cause?
a. temp increase
b. coning
c. foaming
d. deflocculation
b. coning
a mesophilic digester operates in what range?
a. 50 - 68 F
b. 68 - 133 F
c. 113 - 120
d. above 113 F
b. 68 - 133 F
The lab reported the digester sludge analysis as follows: pH 6.6, VA 1,000, alkalinity 1,000. How is the digester functioning?
a. stable
b. feed rate too low
c. floating cover should be raised
d. digester going sour
d. digester going sour - stop feeding immediately
What so facultative bacteria use as a food source when living in anoxic conditions?
a. saprophytes
b. sulfates, polyphosphates, nitrates, etc
c. autotrophic organisms
d. heterotrophic organisms
b. sulfates, polyphosphates, nitrates, et
An activated sludge WWPT with anaerobic digestion gets a high volume of organic load during the week and low organic loading on weekends. This cause pin floc and solids washout on weekends. What can be done to remedy the situation?
a. maintain constant RAS
b. increase RAS on weekends
c. withdraw supernatant on weekends
d. increase sludge age
c. withdraw supernatant on weekends
Supernatant is returned to the head of the plat from the secondary digester. Why not from the primary digester?
a. volatile acid/alkalinity ratio
b. immovable roof
c. primary thief holes higher
d. primary digester contents are completely mixed
d. primary digester contents are completely mixed
Which organisms operate either with or without air?
a. anoxic
b. facultative
c. filamentous
d. protozoan
b. facultative
What keeps a floating coverr from dropping into the water surface?
a. ballast
b. thief holes
c. corbels
d. flame arresters
c. corbels
Flame arresters should be installed where?
a. before the furnace
b. at waste gas burner
c. A & B
d. all the above
d. all the above
When should flame arresters be serviced?
a.annually
b. semiannually
c. daily
d. quarterly
d. quarterly
a glass tube partially filled with a liquid that measures gas pressure is called?
a. meniscus
b. rotameter
c. graduated cylinder
d. manometer
d. manometer
from what point do you read the manometer?
a. bottom
b. top
c. front
d. back
b. top
Which of the following thrive at 60º F?
a. mesophilic
b. psychrophilic
c. saprophytic
d. none of the above
b. psychrophilic
What is the term most often used when washing digested sludge?
a. detritus
b. elutriation
c. deflocculation
d. none of the above
b. elutriation
Rapid withdrawal of sludge from an anaerobic digester causes?
a. heat remission
b. increased pH
c. coning
d. sedimentation
c. coning
Anaerobic digester samples are taken from which point?
a. recirculation pump
b. flame arrester
c. hollow cone
d. thief hole
d. thief hole
What happens on a digester during the acid regression stage?
a.acid decreases
b. pH increases
c. alkalinity increases
d. alkalinity decreases
e. A, B & C
e. A, B & C
A _______ is provided for a floating cover by the __________ ?
a. ballast / corbel
b. access hatch / thief hole
c. gas seal / annular space
d. PRV / corbel
c. gas seal / annular space
What is the purpose of flotation chambers of anaeroic digester floating cover?
a. gas storage
b. breakup scum layer
c. seed sludge
d. prevents cover form sinking into the sludge
d. prevents cover form sinking into the sludge
What has a fusible element that melts causing gas flow to stop?
a. thermal valve
b. chlorine tank
c. thief hole
d. flame arrester
a. thermal valve
What is the simplest way to start an anaerobic digester?
a. raw waste
b. seed sludge
c. primary sludge
d. secondary sludge
b. seed sludge
WWTP records must be kept on site for how many years?
a. 10
b. 7
c. 5
d. 3
d. 3
a WWTP MOR ( Monthly Operating Report)must be received by FDEP (Florida Department of Environmental Protection) by the ___ of the month following the month of operation?
a. 31st
b. 28th
c. 15th
c. 10th
b. 28th
The composited influent sample must insure___ are not included on the sample?
a. digester supernatant, RAS, process wastes
b. screenings, grit
c. screening , grit, RAS
d. trickling filter effluent, RAS, screenings
a. digester supernatant, RAS, process wastes
how often must reuse systems, 0.5MGD or higher samples for TSS, CBOD, and nutrients?
a. 2 days/wk
b.3 days/wk
c. 5 days/wk
d. 7 days.wk
d. 7 days.wk
the gas flame from the digester is yellow. What does that indicate?
a. VA/A ratio of 0.1
b. too mush methane
c. too much carbon dioxide
d. digester temp 99°
c. too much carbon dioxide
What % of the digester gas mixture should be methane?
a. 35%
b. 70%
c. 60%
d. 50 %
b. 70%
What is usually the first sign that a digester is going sour?
a. pH drops
b. temp drops
c. gas production increases
d. VA/A ratio goes up
d. VA/A ratio goes up
What is the best test to use to operate a digester successfully?
a. pH
b. temp
c.VA/A ratio
d. volatile pound removed
c.VA/A ratio
What does alkalinity do in the digester?
a. controls supernatant withdrawal
b. determines sludge withdrawal
c. buffers against the acid
d. controls scum blanket
c. buffers against the acid
When should you measure the sludge blanket for SBR (Sequencing Batch Reactor)?
a.after sludge withdrawal
b. end of idle
c. end of settle cycle
d. after decant
c. end of settle cycle
What lab equipment is used to measure 100 mL accurately?
a. graduated cylinder
b. beaker
c. BOD bottle
d. volumetric pipette
d. volumetric pipette
in an anaerobic digester how does bacteria get oxygen?
a. air bubbler
b. air compressor
c. psychrophilic
d. sulfates and other organisms
d. sulfates and other organisms
high-level disinfection facilities must reduce TSS to____ before application of disinfectant.
a. 20 mg/L
b. 5 mg/L
c. 30 mg/L
d. 15 mg/L
b. 5 mg/L