Effect of the endogenous phase duration on the maximum substrate removal rate in mixed cultures

The maximum substrate removal rates, r x, m , were measured during the endogenous phase by means of a simple respirometric method. Excess biomass from a continuously-fed completely mixed (CM) and a semicontinuously-fed (SE) reactor was tested with ethylalcohol, glutamic acid, phenylalanine, acetic acid, phenol and glucose. It was found with the mixed culture from the CM system that during a 6-h endogenous period, the r x, m values remained constant with all the substrates tested. With the mixed culture from the SE system, the r x, m values increased during first 8–12 h of the endogenous period and then decreased. The authors conclude that the respirometric method measuring r x, m values can be used to optimize the contact stabilization process.