A control system for the in-line coagulation applied in an ultrafiltration process was developed. The dosing strategy aims to apply a minimal coagulant dose while maintaining desirable process performance by regulating the initial filtration resistance. This is achieved by a feedback controller. It was found that the control system performs well; adaptation to changing conditions is achieved adequately and sufficiently fast. The initial resistance of the last filtration before the chemical cleaning phase can be controlled within an accuracy of approximately 3% (of the total resistance) or 9% (of the fouling resistance). Compared to the current dosing strategy, a significant reduction of coagulant consumption can be achieved. (c) 2007 Elsevier B.V. All rights reserved.