Rebirth of Water - 2017-2018

APPENDIX A: CALCULATIONS USED TO DETERMINE WATER QUALITY
PARAMETERS.
A-1: Fecal coliforms:
In determining the total amount of fecal coliforms in a 100 mL of sample a plate count between
20 – 80 coliform bacteria must be counted from a 10 mL sample.
Counted fecal coliforms = counted bacteria ∗ dilution
Where:
counted bacteria = the bacteria counted on a agar plate from a 10 mL sample
dilution = dilution factor of the 10 mL sample
Total fecal coliforms = counted fecal coliforms ∗ 10
Where:
total fecal coliforms = amount of fecal coliforms in a 100 mL sample
counted fecal coliforms = number of coliform bacteria counted on the agar plate
If all plates are less than 20:
total colony counts
total volume filtered ∗ 100
Sample Calculation:
Counted fecal coliforms = 45 ∗ 100 = 4500 CFU
10 mL
Total fecal coliforms = 4500 ∗ 10 = 45000
CFU
100 mL
If plates were less than 20:
(19 ∗ 10) + (2 ∗ 100)
∗ 100 = 1950
CFU
20 mL
100 mL
A-2: Orthophosphates:
To determine the amount of phosphates in a litre sample of water the equation from the
calibration graph (Appendix B) must be used.
Y = 0.7737 ∗ x
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