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 an

d 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

• 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

• ISOLATION OF AQUEOUS NOM– Membrane Filtration: Reverse Osmosis

• Polyamide or polysulfone membrane• Advantages: 1) Rapid; 2) NOM not subjected to extreme p

H values• Disadvantage: 1) Simultaneous concentration of salts; 2) a

portion of NOM can sorb to the membranes

• 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)

• NATURAL ORGANIC MATTER CHARACTERISTICS– Molecular Weight

• Mixtures!• Sedimentation equilibrium on Svedberg Ultracentrifuge• Gel filtration, high-pressure size exclusion chromatography, ultr

afiltration, 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

• 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

• 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

• 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