Abstract : During the last years, the efficiency of pollution removal and sludge treatment processes are major concerns because of the more restrictive legislation related to nutrient discharge. A key point in the field of activated sludge wastewater treatment plants (WWTPs) is the secondary settler efficiency. This paper presents a benchmark study to control, using fuzzy algorithms, the sludge height in a secondary settler. The presented control strategy is based on simple on-line data (influent and recycle flows) and daily analitycal values of the Sludge Volume Index (SVI) allowing the fuzzy algorithm to reduce sludge height variations and thus to increase the settling process efficiency. The developed controller has been applied to the Cassà de la Selva activated sludge WWTP (Spain).
