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

that the nitrifying bacteria are more sensitively inhibited by a given concentration of
chemical toxicant than the heterotrophic bacteria. Thus, failure of the nitrifying process
would occur before the carbonaceous removal process. Blum and Speece (1992) also
reported that Nitrobactor exhibited approximately the same toxicity as aerobic
heterotrophs. Thus, to prevent the interference of the nitrifying system in the toxicity test,
70 mg/L of Nitrogen as NH3-N was added to suppress nitrification (Liebeskind, 1999) in
the bacterial system.
The major biokinetic parameters found in the two systems namely, the bacterial and
yeast sludge are expressed in Table 4.3 and 4.4, respectively. The concentration of free
ammonia produced in the system was also measured using a dissociation equation of
ammonium salt into ammonia and hydrogen ion (Ortiz, et al., 1997). The formulae used for
measuring the free ammonia in given below:
[NH3-N] = 17 [NH4 + -N] 10 pH Eq. 4.1
14 exp [ 6344 / ( 273 + T ) ] + 10 pH
The inhibition was found to be much higher in the bacterial sludge than that of the
yeast sludge. The probable reason for this could be the low oxygen uptake of 0.0030 mg
O2/mg VSS. h compared to that 0.0078 mg O2/mg VSS. h of the bacterial culture even at
an ammonium chloride concentration of 70 mg/L. The complete biokinetic parameters
measured for the yeast and bacterial system are presented in Table C-3 and C-4 of
Appendix C. The free ammonia nitrogen concentration in the bacterial sludge was found to
reach a maximum of 20 mg/L whereas that found in yeast sludge was 0.013 mg/L. It has
been found that the ammonia concentration of 31 to 49 mg/L can cause toxicity (Cheung,
et al., 1997) and at a concentration of 200 mg/L can adversely affects the sludge properties
(Robinson and Maris, 1985). The toxicity of the compound also depends upon the nature
and the composition of the waste. This could be the reason for relatively high toxicity of
the ammonia in the landfill leachate. In a yeast based biological system, it was found that a
free ammonia concentration of 11 mg/L would inhibit the growth of Candida utilis where
the ammonium nitrogen concentration was 350- 520 mg/L (Ortiz, et al., 1997). Relatively
low toxicity in the leachate studies could be attributed to the low pH.
Table 4.3 Effect of Free Ammonia Concentration on Yield Coefficient and the Specific
Growth Rate of the Bacterial Sludge
NH4Cl
(mg NH4-N/L)
Free NH3
(mg NH3-N/L)
Y
(mg VSS/mg COD)
µ
(d -1 )
70 0.44-0.70 0.39 0.093
1000 6.36-10.05 0.38 0.055
1500 9.54-15.07 0.35 0.046
2000 12.72-20.10 0.29 0.031
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