Chapter 2

Characterization of NOM

Mika Sillanpää*, Anu Matilainen**,  and Tanja Lahtinen┼     *Lappeenranta University of Technology, LUT Faculty of Technology, LUT Chemtech, Laboratory of Green Chemistry, Sammonkatu 12, 50130 Mikkeli, Finland     **Finnish Safety and Chemicals Agency, Kalevantie 2, 33100 Tampere, Finland     ┼University of Jyväskylä, Department of Chemistry, Organic Chemistry, Survontie 9 B, 40500 Jyväskylä, Finland

Abstract

Worldwide reports over the last few decades have shown that the amount of natural organic matter (NOM) in surface water is continuously increasing, which has an adverse effect on drinking water purification. For many practical and hygienic reasons, the presence of NOM in drinking water is undesirable. Various technologies have been proposed for NOM removal with varying degrees of success. The properties and amount of NOM, however, can significantly affect the process efficiency. To improve and optimize these processes, it is essential to characterize and quantify NOM at various points during purification and treatment. It is also important to be able to understand and predict the reactivity of NOM or its fractions at different stages of the process. Methods used in the characterization of NOM include resin adsorption, size exclusion chromatography, nuclear magnetic resonance (NMR) spectroscopy, and fluorescence spectroscopy. The NOM in water has been quantified with parameters including ultraviolet and visible, total organic carbon, and specific UV-absorbance. More precise methods for determining NOM structures have been developed recently: pyrolysis gas chromatography-mass spectrometry, multidimensional NMR techniques, and Fourier transform ion cyclotron resonance mass spectrometry. This chapter focuses on the methods used for the characterization and quantification of NOM in relation to drinking water treatment.

Keywords

Characterization; Chromatography; Concentration; Fractionation; Natural organic matter (NOM); Spectroscopy Abbreviations AFM    Atomic force microscopy AOC    Assimilable organic carbon AOPs    Advanced oxidation processes ATR    Attenuated total reflectance BDOC    Biodegradable dissolved organic carbon COD    Chemical oxygen demand DBP    Disinfection by-product DBPFP    Disinfection by-product formation potential DOC    Dissolved organic carbon EEM    Excitation-emission matrix ESI    Electrospray ionization FA    Fulvic acids FIFFF    Flow field-flow fractionation FTICR-MS    Fourier transform ion cyclotron resonance mass spectrometry FTIR    Fourier transform infrared GAC    Granular activated carbon GC    Gas chromatography HA    Humic acids HMW    High molecular weight HMBC    Heteronuclear multiple bond correlation HPLC    High performance liquid chromatography HPSEC    High performance size exclusion chromatography HR-MAS    High resolution magic-angle spinning ICP AES    Inductively coupled plasma atomic emission spectroscopy IR    Infrared LC-MS    Liquid chromatography-mass spectrometry LC-OCD    Liquid chromatography-organic carbon detection MM    Molar mass MWD    Molecular weight distribution NMR    Nuclear magnetic resonance NOM    Natural organic matter OCD    Organic carbon detection PARAFAC    Parallel factor PSS    Polystyrene sulfonate Py-GC-MS    Pyrolysis gas chromatography-mass spectrometry RO    Reverse osmosis RPHPLC    Reversed-phase high-performance liquid chromatography SEC    Size exclusion chromatography SEM    Scanning electron microscopy SHA    Slightly hydrophobic acid SUVA    Specific UV-absorbance TEM    Transmission electron microscopy THM    Trihalomethane TOC    Total organic carbon UV-Vis    Ultraviolet and visible VHA    Very hydrophobic acid

2.1. Introduction

Natural organic matter (NOM) is a complex mixture of organic compounds. Some of this organic matter is negatively charged, and it can possess a wide variety of chemical compositions and molecular sizes (Thurman, 1985; Swietlik et al., 2004). All disinfection methods (chlorine, ozone, chlorine dioxide, chloramines, and UV radiation) reportedly produce their own suite of disinfection by-products (DBPs) and bioreactive compounds in drinking water (Richardson et al., 2007). Present knowledge and experience show that the hydrophobic and high molecular weight (HMW) compounds of NOM are the most significant precursors to DBP formation (Hua and Reckhow, 2007; Chen et al., 2008). Hydrophilic matter may also play a key role in the formation of new compounds during disinfection, especially in waters with low humic components. More efficient removal of NOM requires more knowledge of the organic matter present in raw water, and novel methods have been developed for the characterization of these organic compounds. At the same time, existing methods and techniques have been improved. These characterization methods are used to study the composition of NOM prior to treatment and during various stages of the treatment process (Chen et al., 2007; Sarathy and Mohseni, 2007; Her et al., 2008a; Liu et al., 2008; Tercero Espinoza et al., 2009; Zhao et al., 2009; Liu et al., 2010). The diversity of molecules that constitute NOM and the relatively low concentrations of NOM in water often make characterization difficult. There is, therefore, a significant need for methods that can either accurately characterize NOM in these dilute solutions or isolated or concentrated NOM. The NOM in raw water must be characterized to understand its role in water treatment (Matilainen et al., 2011). Ideally, once the various NOM components and fractions of a raw water source have been determined, the treatment processes that will eliminate the most dominant NOM fractions could be selected. Yet, NOM contains literally thousands of chemical constituents. Thus, it is not realistic to characterize NOM on the basis of individual components, as discussed in the introduction, but it is more practical to identify groups of chemicals with similar properties (Croue et al., 2000). An alternative approach to the characterization of NOM is to study how it reacts to DBP formation and the occurrence of different DBPs in drinking water (Culea et al., 2006; Kanokkantapong et al., 2006b; Chen et al., 2008; Cooper et al., 2008; Richardson et al., 2008; Blodau et al., 2009). The binding potential of NOM with inorganic and organic micropollutants may also be relevant to drinking water treatment (Gjessing et al., 2007; Laborda et al., 2009; Park, 2009). Different unit processes remove different NOM fractions during water treatment (Haarhoff et al., 2010). Therefore, more sophisticated characterization techniques are required (Matilainen et al., 2011). Several complementary methods can provide definitive structural or functional information about NOM, and have been found to correlate well, allowing for comprehensive characterization (Jaouadi et al., 2012; Penru et al., 2013). These analytical methods also provide better information for process design and optimization than the conventional dissolved organic carbon (DOC) measurements. DOC, chemical oxygen demand (COD), UV254, pH, turbidity, and color are common water quality parameters assessed by water treatment facilities in their quality control. Assessment of these parameters does not require sophisticated equipment, is simple and fast to perform, and can be automated. Yet, such assessments offer no information about the characteristics of NOM such as molar mass (MM) or hydrophobicity. Traditionally, humic substances have been classified into three categories based on their solubility: humic acid (HA), fulvic acid (FA), and humin. This is an operational division, however; the terms do not refer to single compounds but to a wide range of compounds of similar origin (Uyguner-Demirel and Bekbolet, 2011). NOM may be characterized by high performance size exclusion chromatography (HPSEC) analysis, which determines the molecular weight distribution (MWD) of NOM (Chow et al., 2008; Korshin et al., 2009), or by fractionation techniques that use resins to divide the mixture of organic compounds of NOM into hydrophilic and hydrophobic fractions (Sharp et al., 2006a,b). Although these parameters provide useful information regarding the change in organic characteristics during treatment and impact on DBP formation, it has...