Wastewater treatment systems have, over the past decades, been subjects for optimization and control research. One of the most intricate problems faced is that direct measurements of the variables of interest are seldom available. A large part of research has therefore been aimed at the extraction of suitable information from indirect measurements such as dissolved oxygen, pH, and oxidation reduction potential (ORP). Even if relatively complex tools, such as neural networks and fuzzy logic, have been used to conceive control laws, advantage is seldom taken of such tools with respect to development of the actual control algorithm. In this paper, a simple yet effective tool is presented that allows the detection of a desired process state by means of the Hotelling’s T2 statistic. The detection tool is generic in nature and is thereby applicable to any process where a certain desired state is to be detected by means of measured variables reflecting the targeted state. Its advantages over formerly proposed co...