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

NH3 + H + NH4 +
At low pH, when H + is high, the equilibrium shifts towards the right direction. This
results in low ammonia concentration. The low percentage inhibition in the yeast system
could be attributed to this, as the operation pH of the yeast system is around 3.5 to 3.8
compared to 6.8 to 7.0 in the bacterial sludge.
Though, the ammonia concentration did not affect the yeast sludge much, it was
found to inhibit the microbial growth in the bacterial system. As the ammonium is present
in high concentration in the leachate, leaching becomes necessary prior to further
biological treatment. Thus, ammonia stripping was done to ensure better efficiency of the
biological system and prevent the inhibition of the toxic compounds to the organisms.
(2) Lead Toxicity
Many researches have shown the presence of toxic compounds in many landfill
leachate (Brown and Donnelly, 1988; Baun, et al., 1999). Other studies have shown that
leachate from a municipal solid waste landfill can be more toxic than the leachate from the
hazardous waste landfill (Brown and Donnelly, 1988; Schrab, et al., 1993; Clement, et al.,
1996). Even though large scale disposal of hazardous toxic metals is no longer practiced,
but small generators such as small businesses and households do continue to dispose
hazardous chemicals in the municipal landfills (Brown and Donnelly, 1988). One of such
compounds is the lead, which is present in the landfill leachate. The source of lead is
probably from plumbing fixtures in the individual homes and other lead-containing
products (such as leaded solder, battery, glass, PVC, and small lead items) which are
disposed of as waste.
Though, lead is found at a concentration lower than 1 mg/L (Chian and DeWalle,
1976; Ehrig, 1983; Keenan, et al., 1984; Robinson and Maris, 1985; Robinson, 1992), an
increased concentration of the lead can pose failure of the biological systems. To find out
the effect of the increasing lead concentration on the activated sludge, toxicity studies was
done with it using lead nitrate as a lead source. The lead nitrate in the bacterial system was
varied from 20-100 mg/L compared to 2-25 mg/L in the yeast system. The lead nitrate used
in the yeast system was lower than that of the bacterial system due to the reason that at
lower pH, lead would easily dissociate as a free ion (Cui, et al., 2000). The lead toxicity
was done as described in section 3.4.2. The biokinetic parameters for the lead toxicity
studies in bacteria and yeast leachate is given in Table C-5 and C-6 of Appendices C. The
substrate concentration in the study was similar to that of the ammonia toxicity study.
The substrate utilization by the yeast and bacterial sludge is presented in Table 4.5. It
is found that the substrate utilization of the bacterial system is higher than that of yeast
sludge. As the soluble lead concentration increased from 0 to 10.98 mg/L, the oxygen
utilization rate decreased from 0.519 mg O2/mg VSS.h to 0.075 mg O2/mg VSS.h. The
percentage inhibition at high concentration was found to be 85%. The inhibition effects of
the lead on the bacterial and yeast system is expressed in Figure 4.10 and 4.11, respectively.
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