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The activated sludge process does not lend itself well to the application of control strategies. Of the numerous factors affecting the capacity and performance of the activated sludge process, the operator can control the return activated sludge (RAS) flow rate to a greater degree than any other, often by simply setting the desired value in a computer system.

This paper describes three effects of the RAS flow rate on the behavior of the activated sludge system:

Influent Kinetic Energy

Flocculent Settling Zone Concentration (Mass)

Compression Zone Concentration Profile (Mass)

Although the paper does not present a complete strategy for determining RAS flow rate and operating strategy due to the unique features of each system, it describes how these factors should be considered by system engineers and operators when approaching activated sludge operations and RAS pumping system designs. The paper focuses only on the hydraulic and solids distribution factors above and does not consider biological affects such as clarifier denitrification or secondary phosphorus release.

The paper concludes by presenting a developing approach that may improve secondary clarifier design, operating and modeling techniques.

Document Type: Research Article


Publication date: January 1, 2004

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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