Dear Sunil: (1) Activated ...

Dear Sunil: (1) Activated Sludge is one of the many ways to treat wastewater.  It is an aerobic system, meaning, the process employs aerobic microorganisms to help us to clean the wastewater, which requires free oxygen to live.  (2) Aeration: a physical process used to transfer free oxygen to the water: it can go from fine bubbles put at the bottom of the thank (like in a fish pond) to letting the water fall through a packed media (stones, plastics, and so; (3) extended aeration is a variation of the activated sludge process in which we use a very high retention time in the aeration tank looking for a lower F/M (Food/Microorganisms) value.  Doing so, we try to produce less final amount of sludge to be disposed and a more stable system but we have a higher initial investment cost and operational cost.