Reverse osmosis (RO) membrane technology cannot be applied for the direct purification of nano-scale particle-containing wastewater due to membrane fouling/clogging problems. In this study, a three-stage pre-treatment process was developed to remove nano-scale particles from wastewater prior to further water purification using RO. The proposed pre-treatment system involved chemical coagulation/flocculation followed by sand filtration (SF) and ultrafiltration (UF). Backgrinding (BG) wastewater, which contained high concentrations of inorganic nano-particles, was used to evaluate the feasibility of this three-stage process for nano-scale particle removal. The BC wastewater (collected from a semiconductor manufacturing plant) had turbidity and suspended solids concentrations of approximately 1403 NTU and 77.8 mg/L, respectively. Up to 98% of the turbidity and particles could be removed through chemical coagulation/flocculation when 2.2 mg/L of polyaluminum chloride was used as coagulant and 0.5 mg/L of polymer was used as flocculant. However, the SF system could not effectively remove the nano-scale particles from BC wastewater directly. More than 99% of the turbidity and particles could be removed with the application of a UF unit [spiral-wound (SW) or hollow-fiber (HF) membrane] after the coagulation/flocculation/SF processes. Results indicate that the three-stage system is appropriate for the pre-treatment of nano-particle-containing wastewater. (C) 2011 Elsevier B.V. All rights reserved.