Application of fuzzy logic for on-line control of a laboratory-scale anaerobic reactor

Abstract

An automatic control system, based on fuzzy logic, has been designed to be used in connection to a laboratory-scale anaerobic reactor. The automatic control system is based on a computer that receives all the data from the sensors through a PLC and the keyboard and, by means of a series of fuzzy control rules, it elaborates a control action that modifies the pumps operation times on the base of one working-cycle. A MATLAB program produces the fuzzy inference and it also takes the control decisions. The inference time reached is about 1 ms. Measurements of pH, ORP, T and reactor water level are constantly relayed to the fuzzy controler. The control system has a series of tools that could be useful to the operator such as simulation screen, evaluation screen and trend graphics. The user interface described allows to work with data not obtained directly by means of sensors, so expensive sensors could be avoided. Thus, the operator can enter data from chemical or biological analyses by the keyboard, and elaborate his own fuzzy control rules and membership functions. Moreover, it is possible to evaluate the impact of control decisions without operating on the process. Therefore, the fuzzy controller is a simple, practical, and low-cost technology and allows the operator to control and modelling the system even if he is not an expert.