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3.4.1 Ammonia Toxicity
The experiments were conducted in a closed 0.9-liter batch respirometer equipped
with a recorder, DO meter, and water jacket vessel to maintain a constant temperature as
shown in Figure 3.3.
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Figure 3.3 Respirometer
The operating conditions for yeast and bacterial culture used in this experiment are
given in Table 3.3. The experiment was conducted with low So/Xo (initial substrate
concentration/biomass concentration) ratio. The oxygen uptake rate (OUR) was measured
until the OUR reaches a constant value, which is approximately equal to OUR in the
endogenous phase (Ekama, et al., 1986). The results from the respirometric experiments
would provide the OUR data which can be applied to evaluate the inhibition effects of
ammonia on the microorganisms. Ammonium chloride (NH4Cl) was used as a source of
ammonia. The NH4-N concentration was varied from 200 to 2,000 mg/L.
Table 3.3 Operating Conditions for Yeast and Bacteria Mixtures in Respirometer
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1. Respiration Cell 2. Water Jacket 3. Air Diffuser
4. DO Probe 5. Magnetic Bar 6. Magnetic Stirrer
7. Expansion Funnel 8. DO Meter 9. Recorder
Operating Conditions Yeast Mixture Bacteria Mixture
pH 3.5 to 3.8 6.8 to 7.0
Temperature ( o C) 30±0.5 30±0.5
MLVSS (mg/L) 800 to 1,000 800 to 1,000
So/Xo ratio 0.01 to 0.02 0.01 to 0.02
Suppressing nitrification None Adding 70 mg/L as NH3-N *
Remark: * Liebeskind (1999)
The experimental procedure for the determination of the inhibitory effects is as
follows:
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