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Secondary Treatment Systems

Extended Aeration Process


The purpose of the secondary treatment system is to oxidize the BOD5 and suspended solids of a waste stream to an effluent being discharged of approximately 90% of the incoming influent. This process is considered  the secondary treatment process. Simple, but very effective -the plant operator can run the settle  ability test to monitor the operation of the system.  Over a one hour period will measure the mixed liquor solids within the aeration zone and plot them on the ideal curve.  If the solid level is very low the blowers are running for too long of a period and vice-versa.  The more air the less solids, the less air the more solids.  The operator will want to maintain approximately 40% solids in the aeration chamber over a 30 minute period.

This process involves providing the exact amount of air for the food to micro requirements.

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To meet today’s secondary treatment effluent limits being discharged from domestic wastewater, an advanced secondary wastewater treatment processes is used to meet those conditions. The Wastewater Depot, LLC secondary treatment system is available for those design flow rates up to 500,000 GPD.  The most common applications this system is used with is our lift stations or flow equalization systems.  The process is called an activated sludge type extended aeration  process.


The flow diagram below shows the return activated sludge being returned from the bottom of the clarifier to the aeration chamber for further treatment.  The clear liquid within the clarifier chamber to pass over the weir and discharge as treated effluent.

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Unique Features

The Wastewater Depot, LLC secondary treatment system features a compact design, automatic air control system, quality components ideal for retro-fitting, ease of installation, and simple operation.

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