Fractionation of Natural Organics

Fractionation of natural organics is required to link characteristics to treatment behaviour. Leenheer et al. (1989) expressed an urgent need to separate the complex mixture of HSs into more homogeneous fractions in order to understand its nature and properties. The fractionation of HS in terms of IVW, functional groups, elemental composition, and other characteristics, is limited by methods and patience (Swift (1985)). 

HA can be precipitated from natural waters by lowering the pH value to 1,0, while the FA remains in solution (Bourbonniere and van Haldeten (1989)). FA has an increased carboxyl and decreased aliphatic content which explains its higher solubility in water than HA (Rasyid et al. (1992)). The acidification step used to precipitate HA, hydrolysed the carbohydrates and altered the subsequent analysis (Clair et al (1996)). 

A more common method used for aqueous organics is the resin adsorption step (XAD8, XAD4), which was described in section 2.4.1 and can be used for concentrates to isolate the desired compounds. This method also requires acidification to separate FA from HA. 

For size or MW fractionation, essentially the same methods as described in section 2.5.4 can be applied as a preparative technique. Limitations are often the low concentrations of fractions, necessitating a concentration step which may induce sample alteration. 

The need for large volumes of material often leads to a scale-up of systems. With UF, for example, hollow fibre systems and stirred cells have been compared for the concentration and fractionation of HS. Kwak and Nelson (1977) showed that retention increased with pressure, decreased with ionic strength and was not concentration dependent. HoUow fibres proved ineffective for UF fractionation compared to flat sheet membranes due to clogging and indiscriminate retention effects (Kiichler et al (1994)). 

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Muller, M. B., Schmitt, D., and Frimmel, F. H. (2000). Fractionation of natural organic matter by size exclusion chromatography—Properties and stability of fractions. Environ. Sci. Technol. 34,4867 872. 

Humic substances are those organic compounds found in the environment that cannot be classified as any other chemical class of compounds (e.g., polysaccharides, proteins, etc.). They are traditionally defined according to their solubilities. Fulvic acids are those organic materials that are soluble in water at all pH values. Humic acids are those materials that are insoluble at acidic pH values (pH < 2) but are soluble at higher pH values. Humin is the fraction of natural organic materials that is insoluble in water at all pH values. These definitions reflect the traditional methods for separating the different fractions from the original mixture. 

Fulvic acids, an important, intermediate size fraction of natural organic matter, are believed to play an important role in the reduction of metals and organic pollutants. Reduction of Mn(III,IV) oxides (Sunda et al., 1983 Waite et al., 1988) and Fe(III) oxides (Waite and Morel, 1984a Waite and Morel, 1984c Finden et al., 1984) by fulvic acid has been examined extensively, under chemical conditions resembling those in the environment. 

Books have been written about HSs, which are the dominant fraction of natural organic matter (NOM). The International Humic Substances Society (IHSS) has been founded, but a common structure of a HS has not yet been widely accepted. The large variety of size, functional groups and origin makes researchers lives difficult and analytical methods remain complex and often lead to irreproducible results. The amount of literature available on HSs is extensive, but the quality of research done is often limited to the methods of analysis available and raw water samples used. Results are mostly incomparable due to the use of very different source materials and extraction methods. 

These findings imply a strong need to remove the smaller fraction of natural organics if regrowth potential is to be controlled. 

Sorption of organophosphorus insecticides to soil particles depends primarily on compound hydrophobicity and the fraction of natural organic matter (NOM) in the soil (19, 20). Mineral phases appear to exert more influence on sorption processes for organophosphorus insecticides than for more extensively investigated hydrophobic organic compounds (e.g., DDT). The sorption of most hydrophobic organic compounds is dominated by NOM when the fraction of soil organic matter, exceeds 0.002 (21). For... 

The fraction of the organics removed that result in synthesis varies, depending on nature and biodegradabiUty of the organics in question. A rough estimate is to assume that one-half is oxidized and one-half synthesized. 

One of the favored organisms for study of cellulolysis by Trichoderma is T. reesei. Consequently, many mutant strains which hyperproduce cellulase have been obtained by treatment with ultraviolet light, gamma irradiation, the linear accelerator, diethyl sulphate and N-methyl-N -nitro-N-nitroso-guanidine (7). Whereas much of the study of T. reesei has been with cellulose as substrate, it is relevant to consider the other fractions of natural lignocelluloses hemicellulose and holocellulose (the combined cellulose and hemicellulose fraction). 

Kaiser, K. Zech, W. (1998) Soil dissolved organic matter sorption as influenced by organic and sesquioxide coatings and sorbed sulfate. Soil Sci. Soc. Am. J. 62 129-136 Kaiser, K. Zech, W. (1999) Release of natural organic matter sorbed to oxides and a subsoil. Soil Sci. Soc. Am. J. 63 1157-1166 Kaiser, K. Zech,W. (2000) Dissolved organic matter sorption by mineral constituents of subsoil clay fractions. J. Plant Nutr. Soil Sci. 163 531-535... 

Leenheer, J. A. 1981. Comprehensive approach to preparative isolation and fractionation of dissolved organic carbon from natural waters and waste waters. Environmental Science and Technology 15 578-587. 

Kaiser, K. (2003). Sorption of natural organic matter fractions to goethite (a-FeOOH) effect of chemical composition as revealed by liquid-state 13C NMR and wet-chemical analysis. Org. Geochem. 34,1569-1579. 

Chen, I, LeBoeuf, E. I, Dai, S., and Gu, B. (2003). Fluorescence spectroscopic studies of natural organic matter fractions. Chemosphere 50, 639-647. 

Ma, H., Allen, H., and Yin, Y. (2001). Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent. Water Res. 35, 985-996. 

Egeberg, P. K., and Alberts, J. J. (2003). HPSEC as a preparative fractionation technique for studies of natural organic matter (NOM). Environ. Technol. 24,309-318. 

Mao, J. D., and Schmidt-Rohr, K. (2004a). Accurate quantification of aromaticity and non-protonated aromatic carbon fraction in natural organic matter by l3C sohd-state nuclear magnetic resonance. Environ. Sci. Technol. 38,2680-2684. 

Smernik, R. J., and Oades, J. M. (2000b).The use of spin counting for determining quantitation in solid state C-13 NMR spectra of natural organic matter 2. HF-treated soil fractions. Geoderma 96,159-171. 

Cheshire, M.V, Berrow, M.L., Goodman, B.A. and Mundie, C.M. (1977) Metal distribution and nature of some Cu, Mn and V complexes in humic and fulvic acid fractions of soil organic matter. Geochim. Cosmochim. Acta, 41, 1131-1138. 

Crum, R.H., Murphy, E.M. and Keller, C.K. (1996) A non-adsorptive method for the isolation and fractionation of natural dissolved organic carbon. Water Res., 30, 1304-1311. 

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