TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

different feeding rates and water flow rates to the tubing. The pH value in the reactors
was kept in the range of 7.3-8.6, which was optimal for nitrification bacteria growth
(Winkler, 1981). The temperature of the reactor was maintained at 20.8±0.4°C.
Figure 2 Schematic of the hydraulic controlled experimental system.
Results and Discussion
Nitrification kinetics
Figure 3 illustrates the typical Michaelis-Menten type response obtained from the reactor
series system at 20ºC. The relationship between TAN removal rate and TAN
concentration started as first-order reaction at low concentrations and approached zeroorder
above approximately 4 mg/l of TAN. Curve fitting the experimental data resulted
in the following expression:
S
μ 20 = 2020 * ( )
(6)
1.
8 + S
Equation (6) implies that the maximum nitrification potential under the experimental
conditions is 2,020 mg TAN-N/m 2 -day. The nitrification rate reaches the 50% potential
at a TAN concentration around 1.8 mg/l.
Both Figure 3 and equation (6) provide additional insights for understanding nitrification
processes. At low concentrations, TAN is assumed to be the limiting substrate since the
dissolved oxygen concentration was maintained above 5 mg/l. As TAN concentration
increased, nitrification rates limitation was switched to DO (Bovendeur et. al. 1990 and
Zhang et. al. (1994). According to Tanaka and Dunn (1982), oxygen becomes the
limiting substrate when the bulk liquid concentration ratio of oxygen to ammonia drops
below 2.72 based on the relative amounts of the two nutrients penetrated to the biofilm.
For a DO concentration in bulk solution of 5.5 mg/l, oxygen becomes the limiting
substrate when the bulk ammonia concentration reaches 2 mg/l. Therefore, the zeroorder
response in Figure 3 is due to a second limiting substrate, oxygen.
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