Laboratory Testing

· COD
1) The sample is refluxed with known amounts of potassium dichromate and sulphuric acid.
2) The excess dichromate is measured by spectrophotometry, as the amount of organic matter is proportional to the potassium dichromate consumed.

· Phosphate
1) Ammonium molybdate is combined with the sample containing phosphate ion and form a yellow colour solution
2) A reducing agent, ascorbic acid is added to produce a blue colour solution that is proportional the amount of phosphate present.

· Hardness
1) EDTA, a tritrating agent is added into the sample.
2) Hardness is present if the dye turns reddish-pink from blue colour.

· Suspended Solids
1) Weigh the filter paper with the ceramic dish.
2) Filter paper is placed on the filtration unit and a sample vessel is attached to filter assembly.
3) The filter paper is left to dry in the over at ±105®C for an hour in the oven
4) Then it is being measured again for the amount of solids on the filter paper

· Chloride
1) An indicator, potassium chromate is added into the sample
2) Silver nitrate is used as a titrant in the process of titration.
3) The titred value is noted when the solution turns reddish-brown and calculated by the formula.

BOD vs COD

There is no correlation between the BOD and COD of the different water collection points. Theoretically, as BOD concentration increases, COD concentration should increase as well. However, our results showed otherwise. The reasons could be that:

1. The COD and BOD values were too low and insignificant to show a strong relation between them.

2. Apart from the grease tap, the other water collection points were relatively low in organic matter that can be chemically oxidized and organic matter decomposable by bacteria. The grease tap contained chemicals with nitrogen/phosphorus compounds in them. These chemicals were mainly soaps, detergents and grease that resulted in the high COD reading.
These nitrogen/phosphorus compounds were later on channeled to plants which absorbed them reducing their concentration greatly in the inlet, outlet and ponds.

3. There had been human error in carrying out the BOD test resulting in inaccurate final values.

Hence, the correlation between COD and BOD values is non-existent and can be ignored in this project.