Application of mathematical tools to improve the design and operation of activated sludge plants. Case study: the new WWTP of Galindo-Bilbao Part II:Operational strategies and automatic controllers

This paper presents a new sensitivity analysis methodology for Activated Sl udge WWTPs. It is based on both (a) the calculation of the range of "manipu lated input variables" that satisfy the restrictions imposed on the "output variables" and (b) on the computation of Isolines of the output variables inside the feasible operating specs. This analysis allows a more precise de scription of the operating constraints, facilitates the understanding of th e steady state behaviour of the process and detects possible areas where th e process is very sensitive to small disturbances. The feasible operating s pace for two Activated Sludge WWTP processes for CN removal (RDN, DRDN), us ing SRT and DO level as "input variables" an well as effluent quality and e xploitation costs as the main "output variabies" is studied. The proposed m ethodology facilitates the selection of the appropriate operational strateg y and the design of automatic controllers. Some examples of the application of this methodology for the design of automatic controllers in a real WWTP are briefly presented.