My research project is on Robust NonLinear Model Predictive Control of a Water-Treatment Aereation Sequencing Batch Reactor (SBR). The removal of pollutants from wastewater is a public health problem that demands technically efficient and cost competitive strategies. The use of sequencing batch reactors (SBR) is one of the main innovative alternatives that has been used for the treatment of water effluents. The problem under consideration consists in computing closed-loop optimal control policies of the aeration profiles under uncertain conditions such that the target values determining water quality are reached in minimum operating time. We propose a robust nonlinear model predictive control scheme to deal with uncertainty in the process model parameters. A sensitivity analysis was carried out to identify the model parameters featuring the strongest influence on model response. The uncertainty was modelled as bounded uncertainty on selected model parameters and a multi-scenario optimization approach was then used for its discretization.