Thesis - faculty.ait.ac.th - Asian Institute of Technology

Where;
J = ∆P Eq. 4.2
µRt
J = Permeate flux (L/m 2 .h)
∆P = Applied pressure (kPa)
µ = Dynamic viscosity (N.s/m 2 )
Rt = Total resistance for filtration or Hydraulic resistance of clean
membrane (m -1 )
The membrane resistance (Rm) of the YMBR was found to be 6.66 x 10 11 m -1 and
that of BMBR was found to be 6.29 x 10 11 m -1 . The membrane used in the study had a
surface area of 0.42 m 2 and pore size of 0.1 µm. Both the membranes had a similar pore
size and almost the same membrane resistance. The membrane resistant is important as
with increasing membrane operation, the membrane resistance tends to increase the
transmembrane pressure, which after a certain limit decreases the flux to a great extent.
During this stage when the transmembrane pressure reaches a maximum, the membrane is
said to be fouled. The effect of the membrane resistance prior to and after fouling has also
been studied which would be discussed in later part of this chapter.
4.3.2 Optimization of HRT in Terms of Membrane Bioreactor Treatment Efficiency
(1) COD Removal Efficiency
The influent COD concentration was maintained around 7,000 to 9,000 mg/L, and
the volumetric loading rate was gradually increased from 6.7 to 17.9 kg COD/m 3 .d by
decreasing HRT from 24 h to 12 h with 4 h decrement. A detailed tabulation of the results
is given in Table E-1 and E-2 of Appendix E for the BMBR and YMBR systems,
respectively. The increase in organic loading in terms of COD concentration and change in
HRT is presented in Figure 4.13. As a real leachate from the transfer station and sanitary
landfill was used, fluctuations in the feed could not be avoided. In all experimental runs,
the MLSS of both the systems were maintained around 10,000 to 12,000 mg/L and DO
concentration of above 2.0 mg/L. Figure 4.14 and 4.15 illustrates the MLSS concentration
and pH, respectively in both the membrane bioreactors. The fluctuations in the pH of the
BMBR reactor could be due to the products if the degradation taking place within the
system.
While treating the medium-aged landfill with membrane bioreactors, the effluent
COD concentration fluctuated with that of the influent concentration. The influent and
effluent COD concentration in the BMBR and YMBR are presented in Figure 4.16. It was
observed that the average COD removal efficiency of the YMBR was slightly higher than
that of the BMBR for varied HRT, though the difference was just marginal. The reason for
the increased run period at 16h HRT was the absence of significant improvement in the
treatment performance in terms of COD removal. In a study conducted by Sun, et al., 2002
found similar results. When an influent wastewater with 2,400 mg/L COD was treated
using a submerged MBR, it was found that a change in HRT from 3 to 6 days did not
significantly affect the performance. The removal efficiency just changed from 92 to 93%.
A high COD removal of the high strength wastewater could be due to the increased HRT
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