Activated Sludge Process involves aeration tank with suspended micro-organisms (MLSS) which degrade organic matter present in effluent. The MLSS is further settled in secondary clarifier and the settled sludge is recirculated back in aeration tank to maintain the MLSS. Air/ Oxygen is supplied either by surface or diffused aeration system. The Hydraulic Retention time (HRT) is around 6 – 7 hrs and Sludge Retention Time (SRT) is between 8 – 15 days.


Extended aeration is similar to Activated sludge process except that it includes higher HRT (8 – 10 hrs) and SRT (20 – 25 days) as compared to activated sludge process and hence produces highly stabilized sludge.


Diffused aeration system shall be used to provide desired oxygen to micro-organisms, which also serves to maintain the reactor contents in a completely mixed regime & dissolve oxygen (DO) level of 2 ppm.


The mixed liquor from aeration tank enters the central well of INDION Secondary clarifier for separation of sludge and liquid. At the end of the aeration period the wastewater and biological mass mixture (mixed liquor) flows in through outlet trough to the INDION Secondary clarifier. Here the suspended solids (MLSS) and liquid are separated by gravity. The separated solids are returned to the aeration tank as return sludge, while the liquid overflows over weir into clarified water tank for further treatment. 

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