The sample collected from the effluent must represent the general status of waste water otherwise the treatment plant based on such samples , will not give the expected results.

For collecting sample two methods are used :-

1) Grab Sample :-

These sample are taken at a point , below the surface where the turbulence is properly mixing the effluent particles.

2) Composite Sample :-

• The grab sample as explained above are collected at a regular intervals during the day and these samples are mixed together.
• The amount of the sample to be mixed is determined on the basis of the rate of flow of the effluent in the stream.
• These composite samples give the average of the impurities of the effluent.