Sewage treatment is carried out in 2 phases, primary and secondary phase. The steps involved in primary treatment phase of sewage are:
a. Physical removal of large and small particles from the sewage through filtration and sedimentation wherein first, floating debris are removed by sequential filtration followed by the grit (soil and small pebbles) are removed by sedimentation.
b. The settled solids form the primary sludge while the supernatant forms the effluent. This effluent is then taken for secondary treatment.
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