This paper presents an evaluation of two full-scale ultrafiltration systems used for the treatment of surface water for the pharmaceutical industry. Plant A operated in dead-end mode and plant B operated in dead-end mode with recirculation, coagulation and air-scouring. Total and irreversible fouling indices were used to evaluate the fouling rate and the hydraulic cleaning efficiency. Statistical analysis of the operational parameters showed that most of the hydraulically irreversible fouling was generated immediately after the chemical cleaning. Nonlinear correlation between fouling indices and the feed-water turbidity indicates a complex phenomenon of membrane fouling and suggests that turbidity should not be used as the only control parameter of an ultrafiltration system. As a result, a new concept of hydraulic and chemical cleaning cycle duration based on fouling indices is proposed. Recirculation during filtration, coagulation, and air-scouring in plant B was demonstrated to have a positive effect on the hydraulic cleaning efficiency compared to plant A. With a shorter backwash duration and a longer chemical cleaning cycle in plant B, approximately 15% of the permeate and 25% of the chemicals will be saved. Fouling indices can be used as a performance indicator and can help to optimize performance of ultrafiltration systems. (C) 2014 Elsevier B.V. All rights reserved.