Correlating TMP increases with microbial characteristics in the bio-cake on the membrane surface in a membrane bioreactor.
Subcritical flux operation is widely practiced in membrane bioreactors (MBRs) to avoid severe membrane fouling and, thus, to maintain sustainable permeability. Filtration at a constant subcritical flux, however, usually leads to a two-stage increase in the transmembrane pressure (TMP): initially slowly, then abruptly. We have investigated the mechanism of this two-stage TMP increase through analyses of the structure and microbial characteristics of the bio-cake formed on the membrane. The MBR was operated under various subcritical and supercritical flux conditions. Under subcritical conditions, we observed the typical two-stage TMP increase. When a constant flux augmented and reached the supercritical conditions, however, the dual TMP change gradually transformed into a steeper, one-stage TMP increase. The second stage TMP increase under the subcritical flux was closely related to the sudden increase in the concentration of extra-cellular polymeric substances (EPSs) at the bottom layer of the bio-cake; we attribute the one-stage TMP increase under the supercritical conditions to the accumulation of microbial flocs and the reduced porosity of the bio-cake under compression. We explain the variation of the EPS concentration in the bio-cake in terms of the spatial and temporal changes of the live-to-dead ratio along the depth of the bio-cake.
Hwang
Byung-Kook
BK
School of Chemical and Biological Engineering, Seoul National University, Seoul, Korea.
Lee
Woo-Nyoung
WN
Yeon
Kyung-Min
KM
Park
Pyung-Kyu
PK
Lee
Chung-Hak
CH
Chang
In-Soung
IS
Drews
Anja
A
Kraume
Matthias
M
D001419:Bacteria / Q000378:metabolism; D018441:Biofilms; D001704:Biopolymers / Q000378:metabolism; D019149:Bioreactors; D011134:Polysaccharides / Q000378:metabolism; D011312:Pressure
D001704:Biopolymers; D011134:Polysaccharides