Chemical Oxygen Demand (COD) Test of Waste Water by APHA Method

COD TEST

INTRODUCTION :-
Chemical Oxygen Demand is the quantity of oxygen required to oxidize the organic matter in water by a strong chemical oxidizing agent.
*This method is applied to domestic and industrial water sample.
PRINCIPLE:-
The sample is refluxed in a strong acid solution with a known excess of potassium dichromate solution in the presence of mercuric sulphate to remove chloride interference and silver sulphate as a catalyst. The excess of potassium dichromate is titrated against ferrous ammonium sulphate using ferroin as an indicator. The amount of potassium dichromate used is proportional to the oxidisable organic matter present in the sample.
REAGENTS USED:-
1. Potassium dichromate solution 0.025N
2. Ferrous ammonium sulphate (FAS) 0.1N
3. COD Acid
4. Ferroin Indicator
5. Mercuric sulphate powder
6. potassium hydrogen phthalate standard.

CALCULATION:-
COD mg/lit =
(blank - sample) × Normality of FAS × 8 × 1000/ Volume of sample
= ( 26.5 - 25.7 ) × 0.0951 × 8 × 1000/20
= 30 mg/litre.
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Видео Chemical Oxygen Demand (COD) Test of Waste Water by APHA Method канала Ashish Singh Chemist