Characterisation of natural organic matter (NOM) removed by magnetic ion exchange resin (MIEX® Resin)

Abstract

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.

Pre-treatment of surface waters for ceramic microfiltration

“…3c). These data are consistent with the findings of previous studies showing some LMW organics to be recalcitrant to coagulation and the removal of high MW BPs by IEX to be marginal (Fabris et al 2007;Huber et al 2011;Humbert et al 2007;Mergen et al 2009;Myat et al 2012). Subsequently, clarification followed by SIX was found to yield very low residual organics concentrations (Fig.…”

Enhanced coagulation with powdered activated carbon or MIEX® secondary treatment: A comparison of disinfection by-product formation and precursor removal

“…When used in isolation or as a primary treatment before coagulation (rather than as a secondary treatment, as we have here) MIEX ® has been shown to outperform EC in removal of UV absorbing NOM (Boyer and Singer, 2005). It also has a capacity to adsorb both hydrophilic and hydrophobic organic acids, adsorbs organic compounds over a large range of molecular weights compared to EC (Drikas et al, 2003;Singer and Bilyk, 2002), and can therefore remove NOM fractions recalcitrant to removal by EC (Fearing et al, 2004;Mergen et al, 2009;Morran et al, 2004).…”

Removal of disinfection by-product precursors by coagulation and an innovative suspended ion exchange process

“…NOM that is of low MW (LMW) and hydrophilic in nature is not as amenable to removal by coagulation. It is therefore available to react with chlorine to form unwanted disinfection by-products (DBPs) (Mergen et al 2009), some of which are potentially harmful to human health (Richardson and Ternes, 2014). Water treatment works (WTWs) faced with treating water containing high levels of natural organic matter (NOM), or difficult to remove organic matter, are therefore finding meeting DBP regulatory requirements much more challenging using conventional treatment methods.…”

“…In many cases it has been shown to achieve very high dissolved organic carbon (DOC), especially relating to charged LMW and hydrophilic organic compounds which can be significant DBP precursors. IEX thus appears to target different organic fractions to coagulation (Bolto et al 2002;Drikas et al 2003;Allpike et al 2005;Mergen et al 2009;Bond et al 2010;Kristiana et al 2010).…”

“…Much of the research into the use of IEX for DBPFP control has focussed on the MIEX process (Singer and Bilyk, 2002;Drikas et al, 2003;Allpike et al 2005;Mergen et al 2009).…”