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Evaluating Clarifier Robustness Using Monte Carlo Simulation

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Secondary clarification is typically used for solids separation prior to effluent discharge, or advanced treatment, at most activated sludge wastewater treatment plants. The secondary clarification process must function properly to assure desired operating performance of the activated sludge treatment process. However, typical operating conditions in activated sludge wastewater treatment plants are usually far from “ideal” or “steady state”. As a result, secondary clarifiers are required to function across a broad range of hydraulic loading conditions with a feed that can be highly variable in its concentration, settling, and thickening characteristics.

Solids flux analysis using the ‘state point’ operating concept has been demonstrated as a useful tool in both the design and evaluation of secondary clarifier performance. Solids flux analysis may be used to determine if clarifier failure by settling, thickening, or overall solids loading rate can be expected for a given operating condition. Specifically, this paper demonstrates the use of a Monté Carlo state point analysis simulation technique to estimate the robustness of a secondary clarification system under a wide range of operating conditions typical of a full-scale activated sludge wastewater treatment plant. Robustness was measured as a “safety factor” defined as the ratio between the critical solids flux and the actual solids flux at the appropriate operating point. Robustness was evaluated for settling, thickening and overall solids loading rate failure modes.

In summary, it is demonstrated that the Monté Carlo simulation assessment of secondary clarifier settling, thickening and solids loading rate safety factors can be a useful tool in predicting clarification system robustness and can aid engineers in developing secondary clarifier designs appropriate for the variability found in the various system inputs that influence secondary clarifier performance.

Document Type: Research Article


Publication date: 2001-01-01

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