Abstract
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.
Highlights
Surface water treatment plants (WTP) face many challenges including stricter regulations on disinfection by-products (DBP) levels imposed by the United States Environmental Protection Agency (U.S EPA)
aluminum sulfate (Alum)- and aluminum chlorohydrate (ACH)-based coagulation was studied in parallel at full scale over a period of three years to investigate DBP formation potential removal
It was found that Alum performed better with regards to DBP formation potential removal because of preferential dissolved organic carbon (DOC) removal
Summary
Surface water treatment plants (WTP) face many challenges including stricter regulations on disinfection by-products (DBP) levels imposed by the United States Environmental Protection Agency (U.S EPA). Water 2016, 8, 318 portion, quantified as dissolved organic carbon (DOC) [2], reacts with chlorine during disinfection to form THMs [3] and HAAs. A robust approach to limit the formation of DBPs is to maximize. Optimization of the coagulation process includes the selection of appropriate coagulant and dose in order to achieve DOC removal levels that will keep the treatment facility in compliance while controlling associated chemical costs. WTPs must be able to adjust their treatment processes as the DOC in the surface water changes, which is a limitation associated with the use of jar tests. The purpose of this study is to compare two coagulants, aluminum sulfate (Alum) and aluminum chlorohydrate (ACH), effectiveness in removal of DOC and DBP formation potential at a full-scale plant that has the ability to run side by side treatment trains utilizing two different coagulants. Further analysis of EEMs of raw and settled water samples was performed utilizing parallel factor (PARAFAC) analysis
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