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The Archie Elledge Wastewater Treatment Plant (WWTP), located in Winston-Salem, NC is owned and operated by the Winston-Salem / Forsyth County Utilities Commission. A step feed modifications project was implemented to achieve the following objectives:

Prevent periodic zoogleal bulking episodes that were caused by high soluble BOD loading and low dissolved oxygen (DO) conditions.

Eliminate the need to overaerate the downstream cells of the basins and reduce electrical costs by applying the organic load along the entire length of the basins.

Maintain current level of phosphorous removal achieved in the activated sludge basins.

Achieve denitrification through the use of anoxic cells at the step feed locations in order to increase energy savings.

BioWin simulation software was used to simulate the plant activated sludge system to determine expected process performance and to estimate potential energy savings. Construction of the project was completed in November 2000. The estimated annual energy savings achieved by the project exceeds 150,000 (29%) and it is estimated that project costs will be recovered in approximately 8.5 years. This paper will discuss the design of the step feed modifications at the plant, phosphorous and nitrogen removal considerations, changes made during construction to improve process performance, operational performance after completion of the retrofit, and the energy cost savings realized from the retrofit.

Document Type: Research Article


Publication date: 2001-01-01

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