Endogenous decay coefficient (k_d)

Endogenous decay coefficient (k_d)

The endogenous decay coefficient is used for designing a complete-mix activated-sludge system.
It accounts for the loss in cell mass due to oxidation of internal storage products for energy for cell maintenance, cell death, and predation by organisms higher in the food chain. Micro-organisms in all growth phases require energy for cell maintenance; however, it appears that the decay coefficient most probably changes with cell age. Usually, these factors are lumped together, and it is assumed that the decrease in cell mass caused by them is proportional to the concentration of organisms present. The decrease in mass is often identified in the literature as the endogenous decay.

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 584