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

The various parameters concerned with biokinetic study of the bacterial and yeast
culture are given in Table C-1 and C-2 of Appendix C. The various biokinetic parameters
were measured using the Monad’s model. The substrate concentrations used in the
experiment from 5 to 40 mg/L and 7 to 42 mg/L with yeast and bacterial culture,
respectively. The rate of growth of the organisms in the bacterial culture was found to be
0.009 to 0.03 mg COD/mg VSS. h and 0.008 to 0.02 mg COD/mg VSS. h in the yeast
culture when the substrate concentration was gradually increased. The maximum yield
coefficient was 0.60 mg VSS/mg COD in the bacterial culture and 0.51 mg VSS/mg COD
in the yeast culture. The important parameters for yeast and bacteria sludge are presented
in Table 4.2. Additionally, estimation of the parameter group (µmax/(Y.Ks)) is used as a
measure for comparing the biodegradation kinetics, as suggested by Grady, et al. (1999).
Comparison of the biokinetic parameters for both yeast and bacteria sludge treating
leachate illustrates that the maximum specific growth rate (µmax) and the substrate
utilization rate (k) were determined to be less than the typical values for domestic
wastewater whereas Y value was in the range of domestic wastewater. There is a case that
the µmax and Y values are higher than usual. This might be noted that the µmax and Y values
are not always indicated the biodegradability because there are other factors that control
the biodegradation kinetics such as enzyme activity and substrate concentration. The yield
coefficient might be high and yet the enzyme activity might be low, resulting in slow
degradation rate. Sometimes the degradation rate might be dependent upon substrate
concentrations. Moreover, the parameter group (µmax/(Y.Ks)) of yeast and bacteria is 1.77 x
10 -3 and 3.06 x 10 -3 L/mg.h, respectively, indicating that the biodegradation of organics by
yeast is less than that of bacteria. Comparison of biokinetic parameters with the other
leachate case studies and the domestic wastewater is expressed in Table 4.2.
Table 4.2 Biokinetic Coefficients of Yeast and Bacteria Sludge for the Leachates
Biokinetic parameters
Type of
Sludge
µmax
(d -1 )
Y
(mgVSS/mgCOD)
k
(d -1 )
µmax/Y.Ks
(L/mg.h)
Reference
Yeast sludge 0.27 0.49 0.51 1.77 x 10 -3 Present study
0.42 0.52 0.81 3.06 x 10 -3 Present study
0.30 0.39 0.77 1.57 x 10
0.45 0.63 0.71
-3
1.00 x 10 -3
Zapf-Gilje and
Mavinic, 1981
0.23 0.50 0.46 1.06 x 10 -4 Gaudy, et al.,
1986
8.16 0.85 9.6 2.8 x 10
0.12 0.67 0.18
-4
0.4 x 10 -4
Bacteria
sludge
Pirbazari, et al.,
1996
0.56 0.36 1.56 1.06 x 10 -4 Chae, et al.,
1999
Domestic 6.00 0.60 2-10 2.08 x 10
wastewater
(0.4-0.8)
-2 Grady, et al.,
1999
In both cases, the maximum specific growth rate (µmax) was found to be less than the
domestic wastewater. This could be the type of organisms prevailing in the domestic
wastewater is different from that of the leachate. Though the maximum specific rate
differed from that of the domestic wastewater, the yield coefficient of both yeast and
bacteria sludge were found to be in the same range as domestic wastewater, while the
substrate utilization rate was lower than that of domestic wastewater. This might be due to
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