Explain the process of secondary treatment given to the primary effluent up to the point it shows significant change in the level of biological oxygen demand (BOD) in it.

During the secondary treatment of the primary effluent how does the significant decrease in BOD occurs?

Select the correct sequence of events in a sewage treatment process. A. Passages of primary effluent into large aeration tanks for mechanical agitation and pumping or air . B. Passage of effluent into the settings tank and formation of activated sludge. C. Physical removal of particles thought filtration and sedimentation . D. Release of effluent from the secondary temperature plant into natural water bodies. E. Growth of useful aerobic microbes into flocs which significantly reduce the BOD.

Given below are the steps involved in sewage treatment. Arrange them in proper sequence and select the correct option. A. Passage of primary effluent into large aeration tanks for mechanical agitation and pumping of air. B. Passage of secondary effluent and formation of activated sludge. C. Physical removal of particles through filtration and sedimentation D. Release of effluent from the secondary treatment plant into natural water bodies. E. Growth of useful aerobic microbes into flocs which significantly reduce the BOD.