Fraction of Biomass that Remains as Cell Debris (fd)

Fraction of Biomass that Remains as Cell Debris (f_d)

In the aeration process of a complete-mix activated-sludge system the biomass growth process goes through several phases. During cell death, cell lysis occurs with the release of cellular materials into the liquid for consumption by other bacteria. A portion of the cell mass (cell wall) is not dissolved and remains as nonbiodegradable particulate matter in the system. The remaining nonbiodegradable material is referred to as cell debris and represents about 10 to 15 percent of the original cell weight. Cell debris is also measured as VSS (Volatile Suspended Solids) and contributes to the total VSS concentration measured in the reactor mixed liquor.

For designing a complete-mix activated-sludge system, where these coefficients come in handy, please take a look at the Summary of the Related Calculators.
More coefficients used for designing a complete-mix activated-sludge system, are gathered in the Table of Coefficients.

source: Metcalf and Eddy, page 586