Effects of pH and antiscalant on fouling of RO membrane for reclamation of spent rinse water from metal plating

This study explored the effects of feed pH and antiscalant on fouling control of RO process for the reclamation of the spent rinse water from a nickel-plating operation. Antiscalants Flocon® 260 (F-260) and PermaTreat® 191 (PC-191) were used. In the RO process, it was found that there was a critical pH value between 4.8 and 6.5, above which permeate pH was lower than the feed pH, but below which the reverse was observed. Therefore, effects of feed pHs at above and below the critical pH value were investigated. The results showed that a feed pH below the critical pH value in the range of 4.2-4.8 could result in reduced RO membrane fouling as well as savings on NaOH. This condition was recommended for use in the reclamation of the spent rinse water. F-260 and PC-191 did not reduce fouling of RO membrane. High boron rejections of above 86% in a RO process were observed in this study and the cause needs further investigation. It was concluded that a low feed pH significantly reduced fouling of RO membrane used, and addition of F-260 or PC-191 into the feed was not recommended in this particular application.