A controller to suppress periodic disturbances on an industrial level control system has been designed. The plant is located in a heavily disturbed environment and has parameter uncertainties and an unknown input delay. The controller has been designed for an integral plant with unknown input delay and unknown gain to adaptively suppress disturbances at the input of the integrator. It is assumed that an estimate of the disturbance can be measured, as it was the case in our industrial plant, and that the disturbance can be predicted ahead in time for at least the input delay time of the system. The resulting controller consists of a standard feedback controller and an 'adaptive plug-in controller' to explicitly compensate for the disturbance. The algorithm is appropriate to use the conventional controller already implemented on the plant and simply add the 'adaptive plug-in'. Simulation results fed by experimental data of the disturbed level control system demonstrate the success of the method in practice.