In order to better understand the phenomenon of organic removal during mineral salt precipitation of RO concentrate, the removal of organics during mineral salt precipitation was studied in a model brackish water system. Laboratory precipitation studies were carried out in batch reactors with on-line monitoring of pH and mineral salt ion concentrations via ion-selective electrodes. Grab samples were taken periodically for DOC analysis, crystal size distribution measurements and imaging of mineral crystals. The results of the study served as a basis for assessing the integration of mineral precipitation with RO desalting so as to attain high recovery and thereby minimize the volume of generated concentrate.
The present results demonstrate that the concentration of organics can be significantly reduced by seeded mineral crystallization. The interaction between the organic and mineral salt precipitation was quantified via the effective rate constants for mineral salt crystallization, while varying the organic concentrations. The results indicate that organic removal during mineral salt precipitation is affected by the evolution of mineral salt crystal size distribution. In addition, the removal of mineral salt precursors was found to be sufficiently high to allow operation of secondary RO desalting while eliminating the problem of membrane scaling.