Expert system for control of anaerobic digesters

Abstract

Continuous anaerobic digesters are systems that present challenging control problems including the possibility that an unmeasured disturbance can change the sign of the steady‐state process gain. An expert system is developed that recognizes changes in the sign of process gain and implements appropriate control laws. The sole on‐line measured variable is the methane production rate, and the manipulated input is the dilution rate. The expert system changes the dilution rate according to one of four possible strategies: a constrained conventional set‐point control law, a constant yield control law (CYCL) that is nearly optimal for the most common cause of change in the sign of the process gain, batch operation, or constant dilution rate. The algorithm uses a t test for determining when to switch to the CYCL and returns to the conventional set‐point control law with bumpless transfer. The expert system has proved successful in several experimental tests: severe overload; mild, moderate, and severe underload; and addition of phenol in low and high levels. Phenol is an inhibitor that in high concentrations changes the sign of the process gain. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 58:13–22, 1998.

Wastewater Treatment Systems: Modelling, Diagnosis and Control

“…• (Chynoweth et al , 1994) and (Pullammanappallil et al , 1992) have proposed expert control systems for anaerobic digestion.…”

Critical analysis of engineering aspects of shaken flask bioreactors

“…The CH 4 and CO 2 percentage can be measured using gas chromatographic methods or infrared measurements. The use of methane production as a process output for control is commonly employed (Renard et al, 1988(Renard et al, , 1991Ryhiner et al, 1992;Boscolo et al, 1993;Polihronakis, Petrou, and Deligiannis, 1993;Ryhiner, Heinzle, and Dunn, 1993;Chynoweth et al, 1994;Ehlinger et al, 1994;Moletta et al, 1994;Pullammanappallil et al, 1991Pullammanappallil et al, , 1992Pullammanappallil et al, , 1998. Pressure sensing is a reliable and straightforward technique for the on-line quantification of gas consumption or production in bioprocesses when only a single gas is involved (Anderlei et al, 2004).…”

Optimization of Raw Material Composition in an Agricultural Biogas Plant

“…As a result from poorly monitored systems, most anaerobic digesters are currently run at a less-than-optimum loading rate to prevent instability occurring in the digester. This instability often inhibits methanogens [27] and results in a decrease of the biogas yields.…”