Effect of sludge retention time on sludge characteristics andmembrane fouling of membrane bioreactor
OUYANG Ke , LIU Junxin
DOI:
Received December 22, 2008,Revised February 24, 2009, Accepted , Available online
Volume 21,2009,Pages 1329-1335
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Three identical membrane bioreactors (MBRs) were operated over 2 years at di erent sludge retention time (SRT) of 10 d, 40 d and no
sludge withdrawal (NS), to elucidate and quantify the e ect of SRT on the sludge characteristics and membrane fouling. The hydraulic
retention times of these MBRs were controlled at 12 h.With increasing SRT, the sludge concentrations in the MBRs increased, whereas
the ratio of volatile suspended solid to the total solid decreased, and the size of sludge granule diminished in the meantime. A higher
sludge concentration at long SRT could maintain a better organic removal e ciency, and a longer SRT was propitious to the growth of
nitrifiers. The performance of these MBRs for the removal of COD and NH4
+-N did not change much with di erent SRTs. However, the
bioactivity decreased as SRT increase. The measurement of specific oxygen uptake rates (SOUR) and fluorescence in situ hybridization
(FISH) with rRNA-targeted oligonucleotide probes testified that SOUR and the proportion of the bacteria-specific probe EUB338 in
all DAPI-stainable bacteria decreased with increasing SRT. The concentrations of total organic carbon, protein, polysaccharides and
soluble extracellular polymeric substance (EPS) in the mixed liquor supernatant also decreased with increasing SRT. The membrane
fouling rate was higher at shorter SRT, and the highest fouling rate appeared at a SRT of 10 d. Both the sludge cake layer and gel layer
had contribution to the fouling resistance, but the relative contribution of the gel layer decreased as SRT increase.
