WASTEWATER GRADE 1 EXAMINATION
QUESTIONS THAT HAVE SIMPLIFIED
ANSWERS
domestic wastewater - correct answer-Comes from schools, homes, hospitals, businesses, light industrial
facilities.
population equivalents - correct answer-100 lbs wastewater per day, .2 lbs TSS/day, .17 BOD/day
industrial wastewater - correct answer-Comes from industries. Compatible wastes can be processed by
the plant. Incompatible wastes are toxic to the plant.
sanitary wastewater - correct answer-The combined domestic and industrial waste waters from
community.
storm water - correct answer-Water that runs off roads, parking lots, and other impervious surfaces
during rain and snow storms
sanitary sewers - correct answer-Convey domestic and industrial waste waters, typically from where they
are generated to the plant.
storm sewers - correct answer-Convey storm water, typically from storm drains directly to a point of
discharge (stream, river, ocean).
combined sewers - correct answer-Convey sanitary waste water combined with storm water.
Reasons to collect samples - correct answer-federal and state regulatory compliance, process control,
trouble shooting, special studies including future designs.
grab sample - correct answer-One time sample. Chlorine residual, coliform tests, settable solids,
dissolved oxygen, pH, grease and oil, sulfide tests.
Time based composite sample - correct answer-Fixed volume of sample is collected after passage of a set
amount of time over a certain time period.
Flow based composite sample - correct answer-Fixed volume of sample is collected after a prescribed
amount of flow has passed through the sampling point, or a volume of sample proportional to the flow is
collected after passage of a prescribed amount of time over a certain time period. This sample can also
be called a flow proportional composite sample.
diurnal flow - correct answer-Low at night between 2 and 5 am, steady steep increase in flow starting
after 5 am, reaching first peak in the late morning or early afternoon, slight decrease through the
afternoon, second peak between 6 and 9 pm, and a tapering off of to the low flows of 2 am.
BOD - correct answer-Depletion of dissovled oxygen in a sample over 5 days at 20c is measured. Direct
measure of the amount of dissolved oxygen consumed by aerobic bacteria over five days, indirect
measure of the organic strength of waste water, used to asses the performance of WTP and the unit
operations and unit processes used in WTP.
, COD - correct answer-This test involves the chemical oxidation of all organics in a sample. Measure of
organic strength of waste water, COD is always greater than BOD, In raw municipal sewage COD is
typically 2 to 4 times greater than BOD, takes 2 hrs to run COD compared to 5 days for BOD therefore
more appropriate for process control.
pH - correct answer-The log of the reciprocal of the the hydrogen ion concentration. PH 6 is 10 times the
hydrogen ion concentration of 7. 5 is 100 times the conc of ph 7.
Total solids - correct answer-TSS + TDS
Settleable solids - correct answer-All settleable solids are TSS but not all TSS are settleable.
Hydrogen sulfide h2s - correct answer-Toxic, flammable and explosive, rotten egg odor, dulls sense of
smell, paralyzes ability to breath, corrosive, heavier than air collects in low lying areas.
Methane ch4 - correct answer-Anaerobic digester have 62-70% methane vol basis. Lel is 5% and uel is
15%.flammable/ explosive. Odorless, not toxic but can asphyxiate at high conc, lighter than air.
Anaerobic digester gas - correct answer-65% methane, 34% carbon dioxide, 1% other inert gases.
Contains less than 1% h2s
Parshall flume - correct answer-Open channel device that constricts the flow in such away that the depth
of flow upstream of the flume is directly related to the flow rate passing through the flume. Does not
measure velocity.
Carbon dioxide - correct answer-Aerobic bacteria exhale carbon dioxide. Anaerobic bacteria produce
carbon dioxide. Non flammable, odorless, not toxic but can asphyxiate at high conc, heavier than air.
Grit - correct answer-Sand, coffee grounds, seeds, small pieces of gravel and metals, eggshells. Removed
by velocity controlled grit chambers or aerated grit chambers. Flow is slowed to 1 f/s
Objectives of primary treatment - correct answer-Remove TSSset and the BOD associated with TSSset,
remove floatable material(scum)
Performance of primary clarifiers - correct answer->95% SS removal, 40-60% TSS removal, 25-40% BOD
removal, detention time 1.5 to 2.5 hrs, weir over flow 10000 to 15000 gal/d ft, hydraulic loading 600 to
1200 gal/d ft2
Hydraulic loading - correct answer-Gal/d ft2 (Surface loading or surface over flow rate) how many gallons
of water per day are passing through each square foot of clarifier surface area. Performance is directly
related to hydraulic loading .
Weir overflow rate - correct answer-Gal/d ft. Divide flow in gal/ day by weir length in units of feet.
Detention time - correct answer-Generally 1 hr minimum. If too long(2.5 -3hrs) then odors may be a
problem in a primary clarifier and BOD removal may be compromised due to solubilization of BOD in the
sludge blanket. Divide vol by influential flow rate.
Primary clarifier performance - correct answer-The BOD and TSS tests should be run on 24hr, flow
weighted primary influent and primary effluent composite samples. SS test should always be a grab
sample.
QUESTIONS THAT HAVE SIMPLIFIED
ANSWERS
domestic wastewater - correct answer-Comes from schools, homes, hospitals, businesses, light industrial
facilities.
population equivalents - correct answer-100 lbs wastewater per day, .2 lbs TSS/day, .17 BOD/day
industrial wastewater - correct answer-Comes from industries. Compatible wastes can be processed by
the plant. Incompatible wastes are toxic to the plant.
sanitary wastewater - correct answer-The combined domestic and industrial waste waters from
community.
storm water - correct answer-Water that runs off roads, parking lots, and other impervious surfaces
during rain and snow storms
sanitary sewers - correct answer-Convey domestic and industrial waste waters, typically from where they
are generated to the plant.
storm sewers - correct answer-Convey storm water, typically from storm drains directly to a point of
discharge (stream, river, ocean).
combined sewers - correct answer-Convey sanitary waste water combined with storm water.
Reasons to collect samples - correct answer-federal and state regulatory compliance, process control,
trouble shooting, special studies including future designs.
grab sample - correct answer-One time sample. Chlorine residual, coliform tests, settable solids,
dissolved oxygen, pH, grease and oil, sulfide tests.
Time based composite sample - correct answer-Fixed volume of sample is collected after passage of a set
amount of time over a certain time period.
Flow based composite sample - correct answer-Fixed volume of sample is collected after a prescribed
amount of flow has passed through the sampling point, or a volume of sample proportional to the flow is
collected after passage of a prescribed amount of time over a certain time period. This sample can also
be called a flow proportional composite sample.
diurnal flow - correct answer-Low at night between 2 and 5 am, steady steep increase in flow starting
after 5 am, reaching first peak in the late morning or early afternoon, slight decrease through the
afternoon, second peak between 6 and 9 pm, and a tapering off of to the low flows of 2 am.
BOD - correct answer-Depletion of dissovled oxygen in a sample over 5 days at 20c is measured. Direct
measure of the amount of dissolved oxygen consumed by aerobic bacteria over five days, indirect
measure of the organic strength of waste water, used to asses the performance of WTP and the unit
operations and unit processes used in WTP.
, COD - correct answer-This test involves the chemical oxidation of all organics in a sample. Measure of
organic strength of waste water, COD is always greater than BOD, In raw municipal sewage COD is
typically 2 to 4 times greater than BOD, takes 2 hrs to run COD compared to 5 days for BOD therefore
more appropriate for process control.
pH - correct answer-The log of the reciprocal of the the hydrogen ion concentration. PH 6 is 10 times the
hydrogen ion concentration of 7. 5 is 100 times the conc of ph 7.
Total solids - correct answer-TSS + TDS
Settleable solids - correct answer-All settleable solids are TSS but not all TSS are settleable.
Hydrogen sulfide h2s - correct answer-Toxic, flammable and explosive, rotten egg odor, dulls sense of
smell, paralyzes ability to breath, corrosive, heavier than air collects in low lying areas.
Methane ch4 - correct answer-Anaerobic digester have 62-70% methane vol basis. Lel is 5% and uel is
15%.flammable/ explosive. Odorless, not toxic but can asphyxiate at high conc, lighter than air.
Anaerobic digester gas - correct answer-65% methane, 34% carbon dioxide, 1% other inert gases.
Contains less than 1% h2s
Parshall flume - correct answer-Open channel device that constricts the flow in such away that the depth
of flow upstream of the flume is directly related to the flow rate passing through the flume. Does not
measure velocity.
Carbon dioxide - correct answer-Aerobic bacteria exhale carbon dioxide. Anaerobic bacteria produce
carbon dioxide. Non flammable, odorless, not toxic but can asphyxiate at high conc, heavier than air.
Grit - correct answer-Sand, coffee grounds, seeds, small pieces of gravel and metals, eggshells. Removed
by velocity controlled grit chambers or aerated grit chambers. Flow is slowed to 1 f/s
Objectives of primary treatment - correct answer-Remove TSSset and the BOD associated with TSSset,
remove floatable material(scum)
Performance of primary clarifiers - correct answer->95% SS removal, 40-60% TSS removal, 25-40% BOD
removal, detention time 1.5 to 2.5 hrs, weir over flow 10000 to 15000 gal/d ft, hydraulic loading 600 to
1200 gal/d ft2
Hydraulic loading - correct answer-Gal/d ft2 (Surface loading or surface over flow rate) how many gallons
of water per day are passing through each square foot of clarifier surface area. Performance is directly
related to hydraulic loading .
Weir overflow rate - correct answer-Gal/d ft. Divide flow in gal/ day by weir length in units of feet.
Detention time - correct answer-Generally 1 hr minimum. If too long(2.5 -3hrs) then odors may be a
problem in a primary clarifier and BOD removal may be compromised due to solubilization of BOD in the
sludge blanket. Divide vol by influential flow rate.
Primary clarifier performance - correct answer-The BOD and TSS tests should be run on 24hr, flow
weighted primary influent and primary effluent composite samples. SS test should always be a grab
sample.
