Math Solutions: Mean Cell Residence Time (MCRT)

Mean cell residence time is defined as an expression of the average time (days) that a microorganism will spend in the activated sludge process — or how long sludge is in the system. It is a critical operating parameter in the biological treatment process, with impact on various other parameters and equations (i.e., other "math solutions").

It may also be important for operators and engineers taking certification exams.

Depending on your required math solution pertaining to MCRT, calculations and unit of expression require explicit formulas. Some common examples are demonstrated below:

Calculate mean cell residence time (MCRT):

Calculate lbs. of mixed liquor suspended solids (MLSS) in an activated sludge system:

Calculate lbs. of MLSS wasted (in days):

Calculate lbs. of total suspended solids (TSS) in effluent:

Calculate flow using MCRT:

Playlist of 10⁺ process control (including MCRT) calculations

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This is the Mean Cell Residence Time (MCRT) solution presentation in my series of “Math Solutions.”  If you have specific wastewater math queries, please submit a question.  

About Dan Theobald:

Known in the industry as “Wastewater Dan,” Daniel L. Theobald, proprietor of Environmental Services (www.esdlt.com), is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on industry experience operating many variants of wastewater treatment processing units and is eager to share with others his knowledge about water conservation.

Theobald serves as an active consultant for industries looking to achieve and maintain improved wastewater treatment at reduced cost. He is a Lifetime Member of the Who’s Who Registry of Professionals and holds numerous certifications from wastewater management regulatory boards and professional organizations. Theobald contributed one chapter to the Water Environment Federation’s (www.wef.org) Manual of Practice # 37 (MOP-37), a technical manual resource guide for biological nutrient removal, published in 2013.