For determination of BOD the sample is diluted with distilled water such that the BOD of the diluted sample is less than about 6.0 mg/ L. The diluted sample is aerated to increase the DO level and seeding done...

Potassium dichromate is added to the sample for digestion of the organic matter present in the sample since potassium dichromate is capable of oxidizing a wide varieties of organic substances almost completely...

Trickling filters are either rectangular or circular in shape and about 2 m deep. They are filled either with coarse, crushed rock or large anth­racite coal or blast furnace slag or broken bricks or graded...