Long-Term Comparison of Disinfection By-Product Formation Potential in a Full Scale Treatment Plant Utilizing a Multi-Coagulant Drinking Water Treatment Scheme

A comparative study of two coagulants, aluminum sulfate ( Alum) and aluminum chlorohydrate ( ACH), used in parallel in a full scale water treatment plant ( WTP) in Ohio from October 2009 to December 2012, was conducted to determine disinfection by-product ( DBP) formation potential removal based on both dissolved organic matter ( DOM) and fluorescence-derived metrics. Water quality parameters and fluorescence intensity of water samples collected before and after coagulation were measured three times per week and fluorescence matrices were analyzed using parallel factor ( PARAFAC) analysis, while DBP formation potential was measured in a weekly basis in pre-and post-coagulation water samples. This study revealed that Alum consistently removed more trihalomethane ( THM) formation potential per mg/L of dissolved organic carbon ( DOC) than ACH. ACH treated waters averaged approximately 33% more THM formation potential when normalized to DOC. Similarly, haloacetic acid ( HAA) formation potential averaged 10% higher in ACH treated waters. From the fluorescence analysis, PARAFAC components C1 and C2 ( humic-like fluorophores groups) removal were 23% and 16% higher, respectively, with Alum when compared to ACH. Monte Carlo simulations, based on neural network models developed from the field data, were performed to compare DBP formation across a wide range of conditions. At similar pH, the model results showed that ACH coagulated water had 13% and 20% higher THM and HAA formation potential, respectively, when compared with Alum. The observations from this study reveal that a coagulant's preferential removal of DBP precursors has an impact on DBP formation despite similar DOC removal.