STD 12 - 8. microbes in human welfare — Biology STD 12 Science — Question

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Primary or physical treatment of sewage is the physical removal of large and small particle from sewage. First, the floating debris is removed by sequential filtration by passing through wire mesh screens. Then, the grit (soil and small pebbles) are removed by sedimentation in settling tank. The sediment is called primary sludge and the supernatant is the effluent