This paper presents and discusses an alternative approach, called fuzzy control theory, which can forecast and control complex, uncertain and/or highly-non-linear systems properly. Building the set of control rules is a very difficult task in fuzzy control and they are generated through on-line operation data in this study, not through experts' knowledge and/or operators' opinions, which is different from conventional applications. The fuzzy control theory can be conveniently used as an aid for automatic control, especially for complex and highly-non-linear systems. The steps using the fuzzy control technique are issued, compared and discussed in this paper and are demonstrated by a case study of a dynamic activated sludge process which is much more complex than other wastewater treatment systems. The effects of forecast and control of the fuzzy controller established from the derived fuzzy model are shown by computer simulation and verified by experiments. The results indicate that the forecast and control utilities of the fuzzy controllers are good and very helpful to the understanding of complex systems.
