Are Activated Sludge Simulation Models Useful to Operators?

Abstract

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.

Mathematical Modelling and Computer Simulation of Activated Sludge Systems

“…Since the level of expertise required and the time to configure and calibrate the models may not be readily available at all plants, the results from simulation models can be converted into a series of convenient operating support charts (Bratby et al 2001). Typical information which the charts provide to the operators include the following:…”

Mitigating the Cost of Denitrification in Fixed Film Plant With Nitrate Recycle

“…As part of the initial design, extensive modeling of unit processes at the plant was performed using clarifier models (Wahlberg et al, 1997;Bratby et al, 2001), trickling filter model (Logan et al, 1987(Logan et al, , 1987a, NTF model (Parker et al, 1995) and Brown and Caldwell's solids contact and aeration model. These separate models were integrated into a plant-wide mass balance model.…”

Anoxic or Anaerobic Selectors: Which Is Better?

“…However, care must be taken in both design and operation to provide adequate dissolved oxygen (DO) control in the aerobic zones (particularly the initial zones) as these zones have relatively high oxygen demands, particularly if the plant is nitrifying. Bratby et al (2001) showed that for one period at the Colorado Springs plant, high SVIs resulted from declining DO values in the aeration zones. Longer-term trends of SVI with DO are shown in Figure 5.…”