Effects of estrone and organic carbon exposure on the transformation of estrone†
Exposure of biomass to estrone (E1) and alternate organic substrates was studied to determine whether cometabolism or multiple substrate utilization is an operating mechanism for the transformation of E1 and if feeding intervals affect the selection of E1 degrading bacteria. Biomass generated in membrane bioreactors (MBRs) was capable of degrading E1 regardless of E1 exposure. Nevertheless, pre-exposed biomass had higher E1 transformation rates (P = 0.05) and un-exposed biomass showed a clear lag phase (6 h) prior to E1 tranformation. These results are consistent with and strongly suggest metabolic transformation of E1 via multiple substrate utilization. In the feeding interval study, longer intervals between feeding periods selected for E1 degraders at high organic carbon loads (100 mg COD L−1 d−1; P = 0.018), but had no effect at low organic carbon loads (30 mg COD L−1 d−1; P = 0.32). A lag phase was observed in E1 transformation during famine periods but was absent during feast periods. This result indicates that the presence of other organic carbon substrates speeds the transformation of E1. This research is the first to demonstrate evidence for the role of multiple substrate utilization in the transformation of E1 and suggests operating conditions to improve selection for and activity of E1 degrading bacteria.