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Are Activated Sludge Simulation Models Useful To Operators?
Author: John R. Bratby, Laird Johnson, Denny S. Parker, Bill Van Derveer
Date: 10/01
Presented at WEF 74th Annual Conference and Exposition, Atlanta, GA October 13-17, 2001

Simulation models, such as BioWin™, are powerful tools which allow environmental professionals to accurately simulate the performance of activated sludge systems. However, the level of expertise required and the time to configure and calibrate the models may not be readily available at all plants. This paper demonstrates how the results from simulation models are converted into a series of convenient operational support charts. Typical information which the charts provide to the operators include the following: • Select the correct operating SRT for a given temperature and effluent ammonia concentration. • Select the number of internal mixed liquor recycle pumps for given temperatures, RAS rates and required effluent nitrate concentrations. • Predict the MLSS concentration at given SRTs, primary effluent loads, and temperatures. This chart is particularly useful when the operator has to predict the impacts of taking activated sludge reactors off line for maintenance or other reasons. • Predict the maximum allowable solids load to the secondary clarifiers to prevent failure. Therefore, the impacts of taking clarifiers off line, or adjusting the RAS rate can be readily determined. By accurately modeling the plant, the principal bottlenecks limiting treatment capacity were identified. The operating dissolved oxygen concentration (DO) limited the nitrification rate and required higher SRTs for adequate nitrification. Low DOs and incomplete denitrification also affected sludge characteristics, which limited the allowable solids loading to the clarifiers.

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