The reject water or retentate generated from membrane application for recovery of water from tannery wastewater treatment contains certain refractory organics. These refractory organics are present in substantial quantity in the condensate of reject water also. Hence the treatment of rejects using conventional methods is rather difficult. In this paper, an attempt has been made to treat the reject water from the reverse osmosis (RO) and nano filtration (NF) operation on tannery wastewater using ozonation treatment technique. Ozonation studies on RO and NF rejects indicate that ozone dose of 80 and 100 mg/min for 60 and 70 min contact time achieves 59 and 78% chemical oxygen demand (COD) reduction, respectively. The mass balance in ozone indicates the ozone consumption for RU and NF rejects varies from 2.4 to 3.4 and 2.8 to 4.5 g/g of COD removed respectively. The results suggest that ozonation of RU and NF rejects would significantly reduce the refractory organic pollutant loading into the environment from wastewater reuse facility. (C) 2011 Elsevier B.V. All rights reserved.