Arrange the following steps of sewage treatment in correct sequence.

A. Degradation of dissolved organic matter.

B. Sequential filtration.

C. Digestion of activated sludge

D. Sedimentation in primary settling tank

The sequence of treating the sewage of cities and towns in sewage treatment plants is sequential filtration to remove the floating and suspended debris, primary sedimentation to remove the grit and soil, digestion of dissolved organic matter in aeration tank by aerobic bacterial and fungi and digestion of flocs or activated sludge by aerobes in anaerobic sludge digestor.