Figure 5 The simulated steady-state amount of nitrite in the effluent as a function of dissolved oxygen according to simulations made by Van Hulle (2005). The simulation was done under the assumption that the process was fed by a substrate containing 100 mg NH +4 - N l âˆ’1 . Elevated levels of nitrite could also have inhibitory effects on the anammox bacteria, further reducing the efficiency of the process. A too high DO level could also allow growth of nitrite oxidisng bacteria (e.g. Nitrobacter) which could disturb the process. A combination of the factors mentioned above will limit the maximum allowed DO level in the reactor for which the process is still effective, i.e., produces dinitrogen gas. This maximum will vary with the conditions in the reactor and the biofilm. Figure 6 show a simulation of how the steady-state production of dinitrogen gas of the process depend on the DO for a certain ammonium load. It is clear that a DO level, during the conditions in the left plot, should not exceed 1.5 mg/l and that the optimal DO level are close to 0.8 mg/l. In the right plot the optimal DO level are close to 1.3 mg/l.
Published on Nov 9, 2011