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

The yeast sludge was collected from the bottom sediments of a pond from the
Nonthaburi landfill site, Thailand. A two-liter container was used for enrichment and was
done using fill-and-draw process. The wastewater feed (having glucose as substrate) was
mixed with a diffused aeration system. The pH was adjusted to 3.5 which is optimum for
yeast growth and can prevent bacterial contamination (Elmaleh, et al., 1996). After 24
hours of aeration, the biomass suspension was allowed to settle for 10 hours. Yeast cells,
normally, settle in the bottom, whereas the acid-tolerant bacteria and filamentous fungi
would remain in the suspension. The bacteria and fungi present in the supernatant were
removed by decanting the supernatant. Around 1.5 liters of supernatant was decanted and
fresh medium was added to the next batch. When MLSS of the yeast biomass exceeded
3,000 mg/L, the enrichment process was accomplished.
b) Bacteria Sludge
The bacterial seed sludge was collected from the aeration tank in the activated sludge
process of a wastewater treatment plant.
3.3.2 Acclimatization
Acclimatization was done in order to obtain a mixed bacterial and yeast culture
which can tolerate leachate containing low biodegradable organics and high ammonia
concentration. Five-liter batch reactors were used for acclimatization through fill-and-draw
process. The operating conditions for the reactors are summarized in Table 3.2.
Table 3.2 Operating Conditions for Yeast and Bacteria Acclimatization
Operating Conditions Yeast Reactor Bacteria Reactor
HRT (h) 24 24
MLSS (mg/L) 10,000 5,000
COD (mg/L) 8,000±1,000 8,000±1,000
Temperature ( O C) 25 to 30 25 to 30
pH 3.5 to 3.8 6.8 to 7.0
Both the reactors were aerated by a diffused aeration system and the pH was adjusted
to 3.5 - 3.8 for yeast growth and 6.8 - 7.0 for bacterial growth, respectively. After 24 hours
of aeration, the biomass was allowed to settle for 3 hours. After 3 hours of settlement, the
supernatant was collected and centrifuged at 4000 rpm for 15 minutes. The experiment was
repeated for the next batch under the same conditions until a COD removal of 70% could
be achieved. Once the COD removal efficiency reached a value greater than 70%, the
acclimatization was presumed to be complete.
3.4 Toxicity Studies
The toxicity studies were done with yeast and bacterial culture. The toxicity of the
culture was tested for different concentrations of ammonia and lead.
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