To Determine The Biochemical Oxygen Demand Of A Given Sample of Wastewater

Theory:

Bio oxygen demand (B.O.D) is the amount of oxygen required for the microorganisms (bacteria) present in the waster water to convert the organic substance to stable compounds such as CO₂ and H₂O,

Organic substance + oxygen bacteria -->CO₂ + H₂O

Bacteria placed in cintact with organic materials will utilize it as a food source in the utilization the organic material will be oxidized to CO₂ H₂O.

B.O.D is considered to be the measure of organic content of the waste, the B.O.D determination has been done by measuring the amount of oxygen utilezed by the microorganic has in the stabilization of wste water for 5 days at 20 C.

For domestic sewage the 5 days B.O.D value (B.O.D) is represent approximately 2/3 of the demand to be consumed of all the oxidization materials were in fact oxidized for measurment of high B.O.D values the waste is required to be dilute the diluted water is carefully manufactured and contains a mixture of salts neccessary for biological activities plus a phosphate buffer to maintain neutral PH.

The water is activated before mixing with sewage.

Apparatus:

Bottle burette, pipette, pipette filter, graduted cylinder

Chemicals:

Manganese sulphate alkali iodide acid concentrated sulphate acid stndard hio sulphate and star itch indicator.

Procedure:

1. Take two B.O.D tubes and half fill it with distilled water.

2. Add 3ml of waste water (polluted water) to the B.O.D tubes with the help of pipit.

3. Now filled the tubes with distilled water and fix stopper on it.

4. Put one of the tubes in incubator at 20 C for 5 days.

5. Add 2ml of alkali iodide oxide and shake well if oxygen is present the color will be brown otherwise while)

6. Add 2ml of concentrated H₂SO and shake well which will give a color which is in resemblance to mustard oil.

7. Take 200ml from this solution in a graduted cylinder and add 1ml of strach indicator to it which will give a yellowish color.

8. Put the gragraduated cylinder below the burette containing standard solution of sodium this sulphate and note the initial reading.

9. Fill dissolved oxygen of the first tube the dissolved oxygen is found in similar way.

10. Find the B.O.D by using the formula

B.O.D (mg/lit) = (zero day D.O - 5 days D.O ) x 300/ml of sample

The BRCES (British Royal Commission Effluent Standard) allows a B.O.D of 20 mg/lit in a treated sewagr to be discharged to body of water.