Waste Water Engineering
To test chemical oxygen demand (C.O.D.) of sewage, organic matter is oxidised by potassium dichromate in the presence of

Nitric acid
Citric acid
Hydrochloric acid
Sulphuric acid

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Waste Water Engineering
In the activated sludge process

Aeration is continued till stability
Aeration is done with an admixture of previously aerated sludge
Sludge is activated by constant stirring
Water is removed by centrifugal action

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Waste Water Engineering
The pressure exerted by

Pressure sewers are designed to be safe in tension
All listed here
The sewage when running full from inside, is called internal pressure
The internal pressure if any, causes tensile stress in the pipe material

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