The objective of this research was to develop on-line measurement and feed-back control strategies for evaluation and optimization of a glucose-fed CSTR digester. Using methane yield as a direct on-line measurement, a model and algorithm were developed and applied for feed-back control and adaptive optimization of the digester for temperature. The model and algorithm were modified and integrated into an expert system to use methane production rate and dilution rate to automatically detect and recover digester abnormal performance resulting from underloading, overloading, and addition of an inhibitor (phenol). On-line fluorometric measurement of NADH, which is a measurement of overall microbial activity, was evaluated for its potential contribution to this control strategy.