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Chapter 4. Natural Organic Matter: Structural Characteristics and Reactive Properties

Chapter 4. Natural Organic Matter: Structural Characteristics and Reactive Properties. ORIGIN OF DISSOLVED ORGANIC CARBON IN AQUEOUS SYSTEMS Microbial degradation of organic matter Oxidative polymerization of phenolic compounds in plants and soils Photolytic degradation of NOM

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Chapter 4. Natural Organic Matter: Structural Characteristics and Reactive Properties

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  1. Chapter 4. Natural Organic Matter: Structural Characteristics and Reactive Properties • ORIGIN OF DISSOLVED ORGANIC CARBON IN AQUEOUS SYSTEMS • Microbial degradation of organic matter • Oxidative polymerization of phenolic compounds in plants and soils • Photolytic degradation of NOM • Nonvolatile organic acids dominant in DOC • Allochthonous: entering the system from the terrestrial watershed(유역) • Autochthonous: deriving from biota (e.g., algae, bacteria, and macrophytes) growing in the water body • Organic matter from different source materials  distinctive chemical characteristics

  2. ISOLATION OF AQUEOUS NOM • Adsorption Chromatography • Ion-exchange resins • Nonionic macroporous resins • XAD-8 resin method • Hydrophobic (acid) fraction (humic fraction) separated from the hydrophilic (nonhumic) fraction • XAD-8 and XAD-4 resins (two-column array) • Hydrophobic acids (humic & fulvic acids): HPOA • Hydrophobic bases: HPOB • Hydrophobic neutrals: HPON • Hydrophilic NOM: HPI • Transphilic neutrals: TPHN • Transphilic acids: TPHA • HPOA & TPHA: account for 50 to 90% of the DOC in most waters • About 20 to 30% of DOC – HPI

  3. ISOLATION OF AQUEOUS NOM • Membrane Filtration: Reverse Osmosis • Polyamide or polysulfone membrane • Advantages: 1) Rapid; 2) NOM not subjected to extreme pH values • Disadvantage: 1) Simultaneous concentration of salts; 2) a portion of NOM can sorb to the membranes

  4. NATURAL ORGANIC MATTER CHARACTERISTICS • Elemental Analysis • C, H, O, N, S, and ash contents: % by weight and specific ratios (C/H, C/O, C/N) • Acid fractions: lower C/O ratios • Base fractions: highest N content  lower C/N • Neutral fractions: lower C/H ratios • Specific UV Absorbance • UV absorbance of a given sample at 254 nm / DOC conc. (m-1 L/mg C) • Strong correlation between SUVA and aromatic-carbon content of NOM • HA > FA > THPA • SUVA: HPOA fraction (HA & FA)

  5. NATURAL ORGANIC MATTER CHARACTERISTICS • Molecular Weight • Mixtures! • Sedimentation equilibrium on Svedberg Ultracentrifuge • Gel filtration, high-pressure size exclusion chromatography, ultrafiltration, small-angle X-ray scattering: model compounds • 490 – 14,500 daltons (atomic mass unit, amu) • Pyrolysis Gas Chromatography/Mass Spectrometry • Generally 700oC (final temperature) • Hydrophobic and hydrophilic acids • Aromatic character – a large peak of phenol • A large proportion of proteins (peaks of toluene, styrene, pyrrole, and benzonitrile) and aminosugars • Humic acids are more heterogeneous than fulvic acids – carbohydrates are the most important class of constituents

  6. REACTIVITY WITH CHLORINE • Adsorption of DBP Precursors Onto XAD Resins • XAD-4 and 8 resins can retain significant fractions of NOM (DBP precursors) • Distribution of DBP Precursors: Hydrophobic and Hydrophilic Fractions of NOM • Chlorine demand: 0.8 to 2.8 mg Cl2/mg C • HPOA (I.e., humic substances) and TPHA: the highest total organic halide (TOX) and TCAA precursors • Hydrophobic NOM fractions (HPOA and HPON): the largest THM formation potentials • TOX precursors: HA > FA > TPHA • HPOA fraction (in particular FA – the most abundant fraction of DOC of surface waters): the major DBP precursors of humic-type waters

  7. REACTIVITY WITH CHLORINE • Relative Proportion of the DBPs • Chloroform: 20 to 25% - depends on pH conditions • THMFP/TOXFP ratio: 0.14 to 0.24 • Sum of THM, TCAA, and DCAA: 37 to 52% of the TOX depending on the fraction • Origin and nature of the NOM  production and distribution of DBPs • More hydrophilic fractions of NOM  more significant precursors of THMs than HAAs

  8. REACTIVITY WITH CHLORINE • Relation with Structure • Electron-rich moieties: extremely vulnerable to electrophilic attack – oxidation and substitution reactions can occur • Aromatic-carbon content: SUVA – TOXFP or THMFP

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