the NaOH and Na,CO, were added to the NaCl, RBS and RO16 mixtures at the fourth step The first run at step with the original pll of the solution, which was about 1.50; CI rejection of 27% was achieved with this solution. The second and third runs were conducted with the acidified solutions using H So, and HCI, respectively, with the Cl rejections of about 20% and 14%. These values were slightly lower than the CI rejection obtained at the first run of this step and at th first three steps of the study. The lowest Cl rejection was achieved at the acidified solution with HCI. Low CI rejections are very important for later reuse of permeate in the dyeing pro- cesses 17]. An increase oftheNaClconcentration in the feed with the addition ofHCIdecreased the osmotic pressure differences further in the feed and permeate due to the Cl concentration in the HCI. Using HCl for acidification increases NaCl recovery at the permeate better than Hrso.