Natural aquatic organic matter (NOM) reacts with chlorinated disinfectants used to treat public drinking water supplies resulting in the formation of toxic and carcinogenic disinfection byproducts (DBPs). Therefore, treatment processes that reduce the concentration of NOM prior to drinking water disinfection have been found to reduce the formation of these unwanted DBPs. Conventional enhanced coagulation was compared with a novel anion exchange resins for reducing DBP precursors located in the negatively charged fraction of the NOM matrix.
Three anion exchange resins (AERs) were compared (IRA-910, IRA-958, and MIEX) to determine which resin would not only remove NOM but DBP precursors as well. All the AERs were found to be highly proficient at NOM reduction specifically the moieties that absorb UV light at 254 nm and 272 nm over 75 minutes of contact time; however, MIEX removed NOM at a faster rate than the Amberlite resins. Results show that pH had no significant effect on the removal of chromophores and fluorophores (i.e. EEM base pairs A and C) when treated with MIEX or enhanced coagulation. Coagulation was effective at removing 30-45% NOM for Akron and Barberton source waters based on peak intensity excitation-emission pairs taken from the EEM (excitation- emission matrix). Peak intensity in the T region of the EEM for the Barberton source water, which correlates to positively charged soluble microbial, was found to be relatively resilient to each NOM removal process.
DBP formation was determined as a function of pH for the different NOM removal processes. MIEX resulted in significant reduction in DBP concentrations for both source waters when compared to DBP formation in the chlorinated raw source waters. MIEX out performed both coagulants reducing the formation of DBPs in both source waters. At an elevated chlorine concentration in the raw samples, as pH increases from 6.5 to 8, chloroform formation increases, TCAA concentrations decrease and dichloroacetic acid (DCAA) is not affected. The two coagulants both reduced DBP formation; however, alum appeared to reduce DBP concentrations more significantly than ACH at pH 8.2.