The aim of the research presented in this paper was to gain greater insight into the characteristics of NOM removed by MIEX® Resin. Previous studies have shown that MIEX® Resin increases the level of removable DOC when used in combination with coagulation, suggesting that these two processes target a different type of organics.
Initially the characteristics of DOC in regenerant solutions from four different MIEX® Resin treatment plants were analysed and compared to DOC in the respective raw water. Following this the raw water and the regenerant solutions were coagulated and the characteristics of the residual DOC analysed and compared to the regenerant solutions prior to coagulation.
From the regenerant solutions it was seen that MIEX® Resin targets DOC of increased UV254 absorbance, increased charge density and of mid to low molecular weight (5 to 2 kDa). In terms of hydrophobicity no preference of MIEX® Resin for a specific NOM type was seen. The presence of hydrophilic neutral acids in the regenerant solution was unexpected since the removal of only highly charged organic species was expected. Charge density measurements however revealed the presence of functional groups, allowing hydrophilic neutrals to be removed by anion exchange. Comparative coagulation of the raw water and regenerant solution showed that both a residual DOC of similar hydrophobicity in the sub 3 kDa area. Considering that this DOC fraction was present in the regenerant it was concluded that MIEX® Resin removes organics recalcitrant to coagulation from raw water and therefore increases DOC removal when both methods are combined.