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The Case for Staging Biological Reactors

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Historically, there has not been technical guidance for the configuration of biological basins with the exception of a 1930's recommendation to compartmentalize the basin. In the 1960s, the complete mix activated sludge (CMAS) process emerged as a dominant design concept, but in the last 15-20 years, there has been a trend to move away from the complete mix concept in recognition of its association with bulking sludge problems. However, many of the rectangular aeration basins with a length:width ratio less than 5:1 still maintain many of the hydraulic residence time characteristics of a complete mix basin. Many factors can be involved in the presence or absence of bulking organisms, both from the design and operation of the biological system. This paper will trace the history of experience and provide evidence linking a good settling, low SVI sludge to multi-staging of the total biological reactor. Bioselection zones and the significance of the dissolved oxygen content in the initial aerated zones will also be addressed.


Document Type: Research Article


Publication date: October 1, 2007

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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 These proceedings are not peer reviewed.

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