An intelligent system for distributed control of an anaerobic wastewater treatment process

This paper describes the design and implementation of an intelligent system by means of which multiple anaerobic systems for wastewater treatment are controlled individually by local controllers which are linked to a common remote central supervisor via wide area networks in a client/server network architecture. The local control systems have a hybrid structure, comprising both algorithmic routines for data acquisition, signal preprocessing, calculation of plant operation parameters, etc., and an expert system based on production rules embodying non-mathematical or semiquantitative knowledge of the unit's operation. The system shows a modular structure, which allows for easy modification or updating with improved versions. The expert system starts up faster than a human operator and maintains the stability of the biological process by modifications in the operating conditions of the plants, reporting warnings and alarms to the central system. The central supervisor acquires, analyses, interprets and stores the data sent by the on-site bioreactor control systems in a relational database, allowing remote specification of plant operating setpoints and continual development of the system. The database is linked with the expert system in order to extend the working memory to the database, allowing its use as an information source. The client/server architecture has been analysed using two different aspects. Firstly, different operating systems were under consideration in the local equipment, in order to determine the networking, multitasking and temporal behaviour. Secondly, different implementations of the network communication were taken into account to make it more flexible, and to allow better adaptation to the communication infrastructure. (C) 2000 Elsevier Science Ltd. All rights reserved.