Activated sludge that originated from a biogenic fed-batch reactor under steady-state was re-cultivated with the same biogenic substrates to test the changes in the sludge's performance in acclimation and degradation of a xenobiotic. Re-cultivations with varying biogenic concentrations were conducted at time points ranging from 16 d before to 4 d after the acclimation reactions. Biogenic re-cultivation energizes sludge cells thereby benefiting the re-cultivated biomass by shortening its acclimation lag time. Lag time increases on both sides of the re-cultivation time where lag has been shortened the most: (1) in short recultivation times before and after acclimation reactions, high concentrations of new or unfinished biogenic substrates cause diauxic growth that delays acclimation; (2) in long re-cultivation times, the re-cultivated biomass loses its energy-rich advantage. Both these lag lengthening situations have their worst cases in which acclimation lag times become longer than that of the original sludge, thus counterbalancing the benefits. (C) 2011 Elsevier Ltd. All rights reserved.