Probing Coagulation Behavior of Individual Aluminum Species for Removing Corresponding Disinfection Byproduct Precursors: The Role of Specific Ultraviolet Absorbance.

He Zhao,Huijuan Liu,Jiuhui Qu,Di Zhang,Chengzhi Hu,Chon-Lin Lee

doi:10.1371/journal.pone.0148020

Abstract

Coagulation behavior of aluminum chloride and polyaluminum chloride (PACl) for removing corresponding disinfection byproduct (DBP) precursors was discussed in this paper. CHCl3, bromine trihalomethanes (THM-Br), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potential yields were correlated with specific ultraviolet absorbance (SUVA) values in different molecular weight (MW) fractions of humic substances (HS), respectively. Correlation analyses and principal component analysis were performed to examine the relationships between SUVA and different DBP precursors. To acquire more structural characters of DBP precursors and aluminum speciation, freeze-dried precipitates were analyzed by fourier transform infrared (FTIR) and C 1s, Al 2p X-ray photoelectron spectroscopy (XPS). The results indicated that TCAA precursors (no MW limits), DCAA and CHCl3 precursors in low MW fractions (MW<30 kDa) had a relatively good relations with SUVA values. These DBP precursors were coagulated more easily by in situ Al13 of AlCl3 at pH 5.0. Due to relatively low aromatic content and more aliphatic structures, THM-Br precursors (no MW limits) and CHCl3 precursors in high MW fractions (MW>30 kDa) were preferentially removed by PACl coagulation with preformed Al13 species at pH 5.0. Additionally, for DCAA precursors in high MW fractions (MW>30 kDa) with relatively low aromatic content and more carboxylic structures, the greatest removal occurred at pH 6.0 through PACl coagulation with aggregated Al13 species.

Highlights

Humic substances (HS), which widely exists in raw water, can react with chlorine in water treatment process to form halogenated disinfection byproducts (DBPs) [1]
The general trend was that lower molecular weight (MW) fractions had more reactive DBPs precursors, especially for trichloroacetic acid (TCAA) precursors
The scores of different MW samples were relatively scattered. This result indicated that the effect of Specific ultraviolet absorbance (SUVA) to DBPs formation potential (DBPsFP) was variable by different MWs

Summary

Introduction

Humic substances (HS), which widely exists in raw water, can react with chlorine in water treatment process to form halogenated disinfection byproducts (DBPs) [1]. For DBPs control, enhanced coagulation is considered to be one of the best available techniques (BATs) [2, 3]. Aluminum salts, such as aluminum sulfate, aluminum chloride (AlCl3) and polyaluminum chloride (PACl) coagulants, are commonly used for reducing DBP precursors in drinking water treatment [4,5,6,7,8]. Previous investigations demonstrated aluminum species showed in situ Al13 species of AlCl3 at pH 5.0 (or aggregated Al13 of PACl at pH 6.0) were preferentially bound to DBP precursors with aromatic and carboxylic structures [7]. Further research reported that hydrophilic and low molecular weight (

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