Transcript Chapter 4. Natural Organic Matter: Structural

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
• 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)
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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
pH 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,
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
• 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 humictype 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