This paper presents the design and analysis of a multivariable robust-adaptive control strategy for a continuous aerobic wastewater treatment bioprocess. The design procedure is developed under the realistic assumption that the bacterial growth rates are uncertain and the influent flow rates are disturbed, but some lower and upper bounds of these uncertainties (possibly time varying) are known. The control structure is achieved by combining a linearizing control law with an interval observer able to estimate lower and upper bounds of unmeasurable states. The performance of the control algorithms are illustrated by simulations performed for a recycled wastewater treatment bioprocess for which kinetic dynamics are highly nonlinear, time-varying and incompletely known. (C) 2012 Elsevier Ltd. All rights reserved.