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

4.2 Biokinetic Studies
Bio-kinetic experiments are important in any biological treatment systems. A
biological system consists of a mixture of organisms with different growth patterns and
degradation rates. The overall growth and degradation rate is important for the degradation
of the pollutants present in the waste. Therefore, bio-kinetic studies were conducted to get
an overall picture of the degradation potential and growth of the microorganisms used in
the degradation pattern.
4.2.1 Acclimatization of Mixed Yeast and Bacterial Sludge
Prior to the biokinetic study, it is necessary to acclimatize the organisms to the
prevailing toxic conditions of the leachate having high COD and ammonia concentrations
along with other humic organic components. After acclimatization of the culture to be used,
a rich mixture of resistant leachate degrading organisms could be obtained. In the present
experiment, bacterial and yeast culture were used to degrade the leachate in the membrane
bioreactors. Preceding acclimatization of the yeast culture, to obtain a wide range of the
yeast species, yeast was enriched using the standard enrichment technique. The enrichment
was completely accomplished once the yeast reached a MLSS concentration of 3,000 mg/L.
The acclimatization and the enrichment of the bacterial and yeast culture was done as
described in section 3.3.2. The pH of the yeast culture was maintained at around 3.5 as
yeast activity is pronounced at low pH and this would also help in preventing bacterial
contamination.
(1) Organic Removal
The acclimatization of the bacterial and yeast culture were done as described in
section 3.3.2 with the simulated medium-aged landfill leachate having characteristic given
in section 3.2 with variation in COD load, which was step-wise increased to finally obtain
an acclimatized culture. The operation conditions for the acclimatization process are
mentioned in the Table 3.2. The organic load while acclimatizing was step wise increased
from 3,800 to 7,300 for bacterial as well as yeast culture. The acclimatization was done
step-wise until a COD removal approximately 70% could be achieved. The changes in the
biomass concentration along with the F/M ratio and COD removal efficiencies were
noticed. These measured parameters are given in Table B-2 and B-3 of Appendix B.
Acclimatization of yeast and bacterial culture took about 67 days. The change in the
COD removal efficiency and the F/M ratio is given in Figure 4.1 and 4.2. It was found that
after 67 days, the COD removal efficiency with yeast culture was higher than that of
bacterial culture. The COD removal efficiency reached 75% in yeast sludge compared to
66% in the bacterial sludge. This indicates that, yeast culture could probably be more
effective in leachate treatment than the bacterial culture. However, as the results obtained
are not sufficient to conclude that yeast system has a better performance than bacteria
system, further investigation is necessary. F/M ratio decreased from 1.01 to 0.62 kg
COD/kg SS.d in the yeast culture and from 1.45 to 1.14 kg COD/kg SS.d in the bacterial
sludge. The difference between the F/M ratios in the bacterial culture was not as much as
the yeast culture. This suggests that the growth of the yeast culture was more prominent
than the bacterial culture. Lower the F/M ratio, the better is the leachate treatment capacity
of the system. This could be the reason for the better removal efficiency of COD by the
yeast culture.
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