Regelungstechnische und verfahrenstechnische Maßnahmen zur Leistungssteigerung kommunaler Abwasserreinigungsanlagen

From 1996 to 2001, the Zentrum für Sensorsysteme ZESS of the University of Siegen conducted several R&D projects at the Municipal Wastewater Treatment Plant of Netphen.
With the technical setup of 1996 or earlier the plant was unable to meet lowered threshold values, which went into effect on 1 st of July 2001. In particular, the parameters ammonianitrogen (NH 4 -N) and total nitrogen (N ges ) turned out to be critical. Conventionally, performance enhancement in wastewater treatment is achieved either by building a new plant or by the constructional extension of an existing one. However, these very cost-intensive approaches could often be avoided by applying less expensive control and process engineering methods, as described in this thesis.
The process engineering method of installing lamella separators inside the activated sludge tank of the plant allows the pre-sedimentation of solid matter. Hence, a bigger number of pollutant-decomposing microorganisms are detained in the aeration tank, increasing the plant’s purification capacity without overloading the sedimentation tank.
In cooperation with associate partners, several control strategies were tested. Insufficiencies of the applied concepts induced the development of control strategies, using fuzzy logic for the determination of a time-variable O 2 -setpoint. The most powerful approach turned out to be a method featuring a fuzzy-controller with a variable structure for O 2 -setpoint generation. It explicitly recognises the most important state variables (NH 4 -N- and N ges -concentration inside the aeration tank). Save compliance with all threshold values has been achieved and the developed system was permanently implemented at the Municipal Wastewater Treatment Plant of Netphen in autumn of 2001. Thus, reconstruction or rebuilding of the plant could be avoided.