2. What is BOD?
Is the amount of dissolved oxygen required to oxidize
the organic compound by living organism in water
sample.
Which occurs at certain temperature over a specific
time period.
Here the organic compound oxidize by CO2 and H2O.
3. Method to determination of BOD
Dissolved oxygen concentration in a sample must be
measured before and after incubation.
Incubation occurs at dark place.
4. Winkler method
Mn2+ and KI are added to the water sample.
In alkaline solution, the dissolved oxygen will oxidize
Mn2+ as Mn4+.
2 MnSO4 + O2 → 2 MnO2
Which appears as brown color precipitate.
In acid medium, the brown color precipitate will
dissolve and back to solution.
5. Cont……
The Mn4+ reduces as Mn2+ while the I- oxidize as I2.
Mn(SO4)2 + 2 I− → Mn2+ + I2 + 2 SO4
2−
Next, the liberated I2 is titrated against standard
S2O3
2− solution.
2 S2O3
2−(aq) + I2 → S4O6
2−(aq) + 2 I−(aq)
8. What is COD?
The COD is a test.
To determine the amount of oxygen that needs to
oxidize all organic compound in water sample
chemically.
COD is normally expressed in ppm OR mg/l.
9. Method to determine the COD
Reflux Method.
‐ Initially add HgSO4.
‐ Add H2SO4 very slowly.
‐ Add Excess amount of K2Cr2O7(aq).
10. Cont….
titrate remaining unreduced K2Cr2O7 with FAS(Ferrous
Ammonium Sulfate), using 2 to 3 drops ferroin
indicator.
At end point, the color change from blue-green to
reddish brown.
11.
12. a = volume of FAS used for blank solution.
b = volume of FAS for used for sample.
m = molarity of FAS.
vs = volume of sample.
