  Due to severe mathematical modeling and calibration difficulties open-loop
feedforward control is mainly employed today for wastewater denitrification,
which is a key ecological issue. In order to improve the resulting poor
performances a new model-free control setting and its corresponding
"intelligent" controller are introduced. The pitfall of regulating two output
variables via a single input variable is overcome by introducing also an
open-loop knowledge-based control deduced from the plant behavior. Several
convincing computer simulations are presented and discussed.
