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Actual vs. Wahlberg-Predicted RAS TSS

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September 29, 2019

GSA, MCRT, SRT, and Sludge Age Defined

I think there is confusion, sometimes, in how operators (which includes me) define the terms mean cell residence time (MCRT), solids retention time (SRT), sludge age, and, though seldom used these days (was it ever used?), Gould sludge age (GSA). In this post I want to have a detailed discuss...

January 15, 2019

The Math You Need, When You Need It

Mean Cell Residence Time (MCRT)

The MCRT is also referred to as sludge age or solids retention time (SRT).

This is the "complete" or full version of the MCRT equation that includes the mass of solids in the secondary clarifiers.

This form of the MCRT equation does not include the mass of solids in the s...

December 19, 2016


Before going into a detailed discussion of the F:M (food-to-mass or food-to-microorganism) ratio I want to let you know about changing views toward this process control parameter. Here are two opposing examples, the first from 1988 and the second from 2011.


This ratio, called the food-to-microorganism or food/mass (F/M) r...

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