Influence of chlorination on metal binding by dissolved organic matter: A study using Log-transformed differential spectra

Abstract

This study employed the method of Log-transformed absorbance spectroscopy to probe interactions of Suwannee River fulvic acid (SRFA) and Aldrich humic acid (AHA) affected by chlorination with Fe(III), Al(III), and Cu(II) ions. Cl2/DOC ratios of 0.2 and 1.0 (mg/mg) were selected to represent chlorine doses that are commonly used in pre-chlorination and disinfection in water treatment processes. Spectroscopic data were interpreted based on non-ideal competitive adsorption coupled with a Donnan electrostatic sub-model (NICA–Donnan model) that was employed to quantify the constants describing relevant complexation equilibria. The data demonstrated that effects of chlorination on dissolved organic matter (DOM) and metal interactions depend on the metal, chlorine dose and intrinsic DOM properties. Fe(III) was observed to form strong complexes with DOM and relatively little change of Fe(III) binding were observed both SRFA and AHA affected by chlorine. The amount of bound Al(III) decreased significantly at high total Al(III) concentrations (>5μM) due to the reducing of phenolic groups after chlorination. The amount of bound Al(III) decreased only slightly for chlorinated SRFA but for AHA Al(III) binding increased at low total Al concentrations (<1μM) due to the generation of additional carboxylic groups after chlorination. It is different from Fe(III) and Al(III), the dominant involvement of Cu–DOM binding is carboxylic groups in both fulvic and humic acid, especially for humic acid, the increase of carboxylic group after chlorination for SRFA at low Cl2 dose and for AHA at both low and high dose lead to increase the total amount of bound Cu(II).