In recent years, the contaminant load in the bleaching process is reduced by installation of oxygen delignification facilities and by the improvement of bleaching sequence. The components in contaminant change, and the molecular weight of the components is becoming lower.
Changes of effluent properties from bleaching process will degrade COD recovery performance in UF membrane facility. In order to improve this COD recovery performance, the experiment of membrane for E/O stage effluent is carried out. In UF membrane process, most part of higher molecular weight components (more than several ten thousand) and about 50% of ten thousand molecular weight components are removed, resulting in 50 to 60% of COD recovery. As for color and AOX, the recovery capacity was more than that for COD.
The processing system, in which UF membrane is combined with RO membrane, is studied to improve COD recovery capability. In this system, permeate from UF membrane is processed by RO membrane and it is found that COD recovery capability improved from 53.5% to 67.0%.
It is also confirmed that the recovery capability for both color and AOX can be improved.