CHARACTERISATION OF NATURAL ORGANICS

In applying reverse osmosis for NOM extraction, the choice of an appropriate river water, preferably high in DOC and low in salt content, is important. Also the choice of a suitable membrane with maximised rejection is critical to avoid the loss of small organics with the permeate. The drawbacks of this method are the concentration of salts and other contaminants. This generally results in a product of high ash content and the salt can lead to precipitation in the concentrate. Particles in the surface water also need to be removed prior to concentrations however this can be achieved with microfiltration (MF). 

UF with a MWCO of 500 Da was used to desalt NOM concentrated with a magnetic resin but high losses of LMW NOM were reported (Hepplewhite (1995), Newcombe et al. (1996), Crum et al (1996)). UF of such a MWCO is also likely to retain salt to some degree. If fractionation is employed prior to desalting, the desalting step may be limited to the lowest MW fraction, thus minimising the loss of organic matter. 

Serkiz and Perdue (1990) reported successful treatment of H2SO4 and Si(OH)4 residues in the RO concentrate with an ion retardation resin with a high affinity for strong acids, but losses of organics were reported. 

Aldrich HA requires purification prior to use. This can be done by dissolution in 0.01 M NaOH to precipitate contaminants. HA is then precipitated from the supernatant at pH 2.0 and collected by 

The characterisation of natural organics is important in order to understand treatment behaviour and to compare results to other waters. The main characteristics of natural organics are molecular weight, functional groups, hydrophobicity and charge. Results obtained are often relative, depending on the method used and thus var) greatly, even for identical compounds. It seems impossible to measure absolute values and it is therefore important to determine a repeatable method to achieve comparable results and, where possible, apply different methods. 

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Gibert, O., de Pablo, J., Cortina, J. L. and Ayora, C. (2004). Chemical characterisation of natural organic substrates for biological mitigation of acid mine drainage. Water Res. 38(19), 4186-4196. 

Croue J.-P., Labouyrie-Rouillier L., VioUeau D., Lefebvre E., Legube B. (1996), Isolation and characterisation of natural organic matter from surface water / comparison of resin adsorption and membrane filtration isolation procedures. Natural Organic Matter Workshop, Poitiers, France, September 96, 6. 

Newcombe G., Drikas M. (1996), Characterisation of natural organic material om Myponga Reservoir and the effect on activated carbon adsorption, Proc. of WaterTECH, AWVQ A, Sydney, May 96, 442-447. 

Solid state NMR techniques, such as CP, RAMP CP, CP TOSS, MQ DEPT, 2D HETCOR, which are relevant to the characterisation of natural organic matter have been reviewed by Cook. The pros and cons of many of the techniques are compared in an effort to provide guidance to the most beneficial utilisation of the NMR techniques for researchers interested in natural organic matter. 

Matilainen A, Gjessing ET, Lahtinen T, Hed L, Bhatnagar A, Sillanpaa M. An overview of the methods used in the characterisation of natural organic matter (NOM) in relation to drinking water treatment. Chemosphere 2011 83 1431-1442. 

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