| "Several troubles are reported about accumulated microorganisms in the reclaimed water distribution systems. This paper presents the results of residual organic matter (OM) removal and apparent bacterial regrowth potential of treated wastewater obtained from laboratory-scale experiments using advanced biological treatments: two immobilization process in series and a membrane bioreactor (MBR) process. Furthermore, a nanofiltration (NF) membrane process was applied to effluents of the both advanced biological treatments. The immobilization process removed large molecular weight (MW) fractions > 5000 since immobilized microorganisms had sufficiently acclimated. The NF membrane was more effective in rejecting large MW fractions in the effluents of the immobilization and the MBR treatments. But it was difficult to reject small MW fractions < 1000 by NF. Neutral hydrophilic fraction of DOC was reduced by the both advanced biological processes, and it can be thought that the microorganisms in the advanced processes could decompose and grow on the some part of the neutral hydrophilic fraction. Quantity of attached microorganisms in the second immobilization reactor was significantly reduced compared to that in the first immobilization reactor. Therefore, it suggests that apparent bacterial regrowth potential is controlled by the accumulation of effective microorganisms in the first reactor." |
