Guest Column | October 22, 2015

Math Solutions: Activated Sludge – No. 2

Wastewater Dan Theobald

By Daniel Theobald, "Wastewater Dan"

“Wastewater Dan” provides a second round of math solutions devoted to activated sludge calculation requirements.

Designed for both on-the-job and test-preparation purposes, these video tutorials offer mathematical templates for performing accurate wastewater calculations. Of the many topics addressed in the series, the initial set of solutions for waste activated sludge (WAS) has proved most popular.

This follow-up provides additional calculations that may be needed for activated sludge processes. In addition to operators, they may also serve educators, engineers, regulators, and others.

Depending on the calculation used, converting the unit or time of expression may be required for an accurate calculation.

Calculate Hydraulic Residence Time Hours (HRT):

Calculate Sludge Age (Days):

Calculate Food to Mass (F/M or F:M) Ratio:

Complete playlist of Wastewater Dan’s Math Solutions

This is the 'Activated Sludge – No. 2' 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 (, 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 ( Manual of Practice # 37 (MOP-37), a technical manual resource guide for biological nutrient removal, published in 2013.