Environmental Engineering Reference
In-Depth Information
C oMposite s aMpling p roCedure and C alCulation
Because knowledge of the procedure used in processing composite samples is
important to water/wastewater operators, the actual procedure used is covered in
this section:
1. Determine the total amount of sample required for all tests to be performed
on the composite sample.
2. Determine the average daily flow of the treatment system.
Note: Average daily flow can be determined by using several months of data,
which will provide a more representative value.
3. Calculate a proportioning factor:
Totalsample volumere
quired(mL)
Proportioning factor
=
(16.3)
No.ofsamples
×
Averagedaily fl
ow (MGD)
Note: Round the proportioning factor to the nearest 50 units (e.g., 50, 100, 150) to
simplify calculation of the sample volume.
4. Collect the individual samples in accordance with the schedule (e.g., once/
hr, once/15 min).
5. Determine the flow rate at the time the sample was collected.
6. Calculate the specific amount to add to the composite container:
Required volume (mL) = FlowT T × Proportioning factor
(16.4)
where T = time sample was collected.
7. Mix the individual sample thoroughly, measure the required volume, and
add to a composite storage container.
8. Keep the composite sample refrigerated throughout the collection period.
Example 16.5
Problem: The effluent testing will require 3825 mL of sample. The average daily
flow is 4.25 MGD. Using the flows given below, calculate the amount of sample to be
added at each of the times shown:
8 a.m.
3.88 MGD
9 a.m.
4.10 MGD
10 a.m.
5.05 MGD
11 a.m.
5.25 MGD
12 noon
3.80 MGD
1 p.m.
3.65 MGD
2 p.m.
3.20 MGD
3 p.m.
3.45 MGD
4 p.m.
4.10 MGD
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