The design and implementation of a new adaptive controller for anaerobic digesters is presented using a general nonlinear mode! and an uncertainties estimation scheme. The primary advantage of this controller over standard adaptive controllers is that biogas flow rate measurements are not required. The resulting controller is similar in form to standard adaptive controllers and can be named analogously. The adaptive control strategy has been implemented in a pilot-scale anaerobic digester showing good performance and robustness against changes in the feed load.