TM 5-814-3/AFM 88-11, Volume III
Three-stage systems are essentially a combination of separate stage nitrification and denitrification (fig 15-5).
The advantage of this system is its flexibility of operation and the main disadvantage is the capital cost
involved. This configuration also works to prevent short circuiting, which can be a problem in nitrification-
denitrification when plug flow is not achieved. The specific design factors are the same as for the individual
processes involved. Three-stage biological treatment can achieve nitrogen removals of over 95 percent.