wastewater grade 1 exam Treatment updated
20-24/2025
domestic wastewater
Comes from schools, homes, hospitals, businesses, light industrial facilities.
population equivalents
100 lbs wastewater per day, .2 lbs TSS/day, .17 BOD/day
industrial wastewater
Comes from industries. Compatible wastes can be processed by the plant. Incompatible wastes are
toxic to the plant.
sanitary wastewater
The combined domestic and industrial waste waters from community.
storm water
Water that runs off roads, parking lots, and other impervious surfaces during rain and snow storms
sanitary sewers
Convey domestic and industrial waste waters, typically from where they are generated to the plant.
storm sewers
Convey storm water, typically from storm drains directly to a point of discharge (stream, river, ocean).
combined sewers
Convey sanitary waste water combined with storm water.
Reasons to collect samples
federal and state regulatory compliance, process control, trouble shooting, special studies including
future designs.
grab sample
One time sample. Chlorine residual, coliform tests, settable solids, dissolved oxygen, pH, grease and
oil, sulfide tests.
Time based composite sample
Fixed volume of sample is collected after passage of a set amount of time over a certain time period.
Flow based composite sample
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
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
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
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
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
TSS + TDS
Settleable solids
All settleable solids are TSS but not all TSS are settleable.
Hydrogen sulfide h2s
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
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
65% methane, 34% carbon dioxide, 1% other inert gases. Contains less than 1% h2s
Parshall flume
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
Aerobic bacteria exhale carbon dioxide. Anaerobic bacteria produce carbon dioxide. Non flammable,
odorless, not toxic but can asphyxiate at high conc, heavier than air.
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