The paper describes work toward development of a convenient decision support system to improve everyday operation and control of the wastewater treatment process. The goal is to help the operator detect problems in the process and select appropriate control actions. The system comprises subsystems for database management, data analysis including several statistical methods, and expert advice. The statistical methods investigated include construction of external reference distributions, computation of moving averages, graphical methods, discriminant functions for early detection of upsets and several kinds of control charts. The latter two methods are not built into the expert system. Reference distributions are used to help define fuzzy terms such as high and low for the conditions of the variables involved in the expert system control rules. The system is written in dBase-III and Lotus 1-2-3 and has a user-friendly interface for communication between the user and the system.