Ultrafiltration (UF) pretreatment and reverse osmosis (RO) were used to treat the blowdown water from circulating cooling water system. The UF product water meets the requirements as RO feed water. To optimize the operation of cooling water system with UF-RO and to ensure a satisfactory cooling water quality within the JRA (Japan Refrigeration and Air Conditioning Industry Association) water standard. a reasonable concentration factor was determined. The results suggest that when the concentration factor was maintained at 1.3, the cooling water could meet the JRA water standard, and the makeup tap water rate was minimal. Calculated Langelier saturation index (LSI) and electrochemical measurements indicate that cooling water had a very slight scaling tendency, and would not cause corrosion. Finally, a comparative cost analysis between applying UF-RO treatment and adding chemical inhibitors in cooling water system was carried out, it is concluded that applying UF-RO in air conditioning circulating cooling water system is more economical. (c) 2009 Elsevier B.V. All rights reserved