Wastewater grade 1 exam Questions and Correct Answers
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How to control growth rate of microorganism in a aeration basin - ANSWER-Wasting WAS.
Mass of microorganism that will grow in activated sludge system is controlled by..... - ANSWER-Mass of
bod influent , growth rate being maintained, temperature of waste water.
WAS flow rate controls .... - ANSWER-Nitrification, mlss conc, sludge quality, effluent quality, secondary
clarifier capacity, secondary clarifier sludge blanket depth, oxygen requirements , occurrence of some
foam causing organisms.
How to fix WAS flow rate to achieve optimal sludge quality... - ANSWER-Maintain constant mlss or
moves conc or mass, maintain a constant mcrt, maintain constant food to microorganism ratio.
Mlss and mlvss are what type of variables - ANSWER-Response variables not control variables.
MCRT - ANSWER-Average time a single bacterium spends in the activated sludge system before it is
intentionally removed in the WAS or unintentionally removed in effluent. Range 5 to 15 days.
MCRT= (lbs of mlss ab+sec)/ (lbs/d of TSS leaving the system in effluent and WAS)
S - ANSWER-Lbs of mlss in system ab + secondary.
E - ANSWER-Lbs per day of TSS unintentionally lost in effulgent
W - ANSWER-Lbs per day of TSS intentionally removed in the WAS.
Food to microorganism ratio - ANSWER-F:m may be used to determine the conc of mlvss and mlss to be
maintained in the aeration basin. Typical ratios are .2 to .5 lb BOD/d lb mlvss. Extended aeration and
oxidation ditches operate at f:m ratios of .03 to .1 BOD/ d lb mlvss. F/m= ( lbs bod per day to AB)/(lbs of
mlvss in AB)
, How are mcrt and f/m related - ANSWER-Inversely related.
RAS - ANSWER-Control of RAS flow is necessary to ensure an adequate supply of microorganisms must
be returned to the aeration basin to treat influent waste. The sole purpose of the RAS is to keep the
biomass in the aeration basins and out of the secondary clarifiers. Typical RAS rate is 25-50 %, but
depends on mlss conc and the settleablity of the mixed liquor. Extended aeration rates are 75-150%.
Optimum RAS flow rate is the lowest possible that does not result in a significant secondary sludge
blanket.
Sludge volume index - ANSWER-How well activated sludge and mixed liquor solids compact. Not a
settleablity test. Units ml/g of activated sludge after 30 min of settling. Mlss conc must be measured on
the same sample used in the settling test. Ranges are 80 to 120 ml/g. Greater than 150ml/g are
considered bulking sludge.
Standard rate trickling filter - ANSWER-HL= 25-100gpd/ft2, OL= 5-25 lb bod/ d 1000 ft3 of media, media
is 6-8 ft rock, recirculation during low flows.
High rate trickling filter - ANSWER-HL= 100-1000 gpd/ft2, OL= 25-300 lb bod/d 1000ft3 of media, media
3-5 ft natural or synthetic, yes recirculation.
Roughing filter - ANSWER-OL= greater than 300 lb of BOD/ d 1000ft3. Generally used to reduce organic
loading to downstream biological treatment processes.
Disinfection - ANSWER-Kills pathogenic organisms. Does not sterilize.
Chlorine - ANSWER-Powerful oxidizing agent. Greenish yellow color, pungent similar to bleach
detectable at .2 to .4 ppm, 2.5 times heavier than air will sink to low points, boiling point is -29.15 f,
escaping liquid chlorine will turn into gas immediately, one volume of liquid cl2 converts to 460 volumes
of gas. Vaporizes from skin to cause frostbite, not explosive or flammable but can react violently with
many substances. Severe irritant, when mixed with water it forms acid, primary route of exposure is
eyes and respiratory system.
OSHA max level chlorine exposure - ANSWER-1 ppm
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How to control growth rate of microorganism in a aeration basin - ANSWER-Wasting WAS.
Mass of microorganism that will grow in activated sludge system is controlled by..... - ANSWER-Mass of
bod influent , growth rate being maintained, temperature of waste water.
WAS flow rate controls .... - ANSWER-Nitrification, mlss conc, sludge quality, effluent quality, secondary
clarifier capacity, secondary clarifier sludge blanket depth, oxygen requirements , occurrence of some
foam causing organisms.
How to fix WAS flow rate to achieve optimal sludge quality... - ANSWER-Maintain constant mlss or
moves conc or mass, maintain a constant mcrt, maintain constant food to microorganism ratio.
Mlss and mlvss are what type of variables - ANSWER-Response variables not control variables.
MCRT - ANSWER-Average time a single bacterium spends in the activated sludge system before it is
intentionally removed in the WAS or unintentionally removed in effluent. Range 5 to 15 days.
MCRT= (lbs of mlss ab+sec)/ (lbs/d of TSS leaving the system in effluent and WAS)
S - ANSWER-Lbs of mlss in system ab + secondary.
E - ANSWER-Lbs per day of TSS unintentionally lost in effulgent
W - ANSWER-Lbs per day of TSS intentionally removed in the WAS.
Food to microorganism ratio - ANSWER-F:m may be used to determine the conc of mlvss and mlss to be
maintained in the aeration basin. Typical ratios are .2 to .5 lb BOD/d lb mlvss. Extended aeration and
oxidation ditches operate at f:m ratios of .03 to .1 BOD/ d lb mlvss. F/m= ( lbs bod per day to AB)/(lbs of
mlvss in AB)
, How are mcrt and f/m related - ANSWER-Inversely related.
RAS - ANSWER-Control of RAS flow is necessary to ensure an adequate supply of microorganisms must
be returned to the aeration basin to treat influent waste. The sole purpose of the RAS is to keep the
biomass in the aeration basins and out of the secondary clarifiers. Typical RAS rate is 25-50 %, but
depends on mlss conc and the settleablity of the mixed liquor. Extended aeration rates are 75-150%.
Optimum RAS flow rate is the lowest possible that does not result in a significant secondary sludge
blanket.
Sludge volume index - ANSWER-How well activated sludge and mixed liquor solids compact. Not a
settleablity test. Units ml/g of activated sludge after 30 min of settling. Mlss conc must be measured on
the same sample used in the settling test. Ranges are 80 to 120 ml/g. Greater than 150ml/g are
considered bulking sludge.
Standard rate trickling filter - ANSWER-HL= 25-100gpd/ft2, OL= 5-25 lb bod/ d 1000 ft3 of media, media
is 6-8 ft rock, recirculation during low flows.
High rate trickling filter - ANSWER-HL= 100-1000 gpd/ft2, OL= 25-300 lb bod/d 1000ft3 of media, media
3-5 ft natural or synthetic, yes recirculation.
Roughing filter - ANSWER-OL= greater than 300 lb of BOD/ d 1000ft3. Generally used to reduce organic
loading to downstream biological treatment processes.
Disinfection - ANSWER-Kills pathogenic organisms. Does not sterilize.
Chlorine - ANSWER-Powerful oxidizing agent. Greenish yellow color, pungent similar to bleach
detectable at .2 to .4 ppm, 2.5 times heavier than air will sink to low points, boiling point is -29.15 f,
escaping liquid chlorine will turn into gas immediately, one volume of liquid cl2 converts to 460 volumes
of gas. Vaporizes from skin to cause frostbite, not explosive or flammable but can react violently with
many substances. Severe irritant, when mixed with water it forms acid, primary route of exposure is
eyes and respiratory system.
OSHA max level chlorine exposure - ANSWER-1 ppm
