| Tannins (plant polyphenols) are the materials of many kinds of industries, such as printing and dyeing industry and leather industry. And they are also widely used in Medicine Industry and as food assistant agent. So tannins exist in much industry waste water. Because of their widely existing in different waters, especially in water bodies of forest area, their effects on water treatment cannot be ignored. Considering that tannins could reappear and replace NOM as well as their relatively explicit structure,we definitely choose tannins as study object. In this paper, tannic acid is choosed to be the representative of tannins and its chemical behaviors related to the water treatment processes is studied by modelling water samples.The molecular weight of tannic acid is almost equal to that of NOM in surface water. As humic acid and fulvic acid,colloidal stability, oxidation, hydrolysis and complexation of tannic acid will cause influence on feed water treatment processes. The key question of improving the quality of drinking water is to removal the harmful hence organic pollutants in order to reduce the formation of DBPs. Basic research has been done to solve the problems above.Accurate determination of tannic acid is the foundation for the study of tannic acid. UV Spectrophotometry , internal standard method of fourier transform infrared(FTIR) and HPLC are used to determine the concentration of tannic acid in water and satisfactory results are gained. Using HPLC only is not superior to the other two methods, but united use of HPLC and IC will make it have superiority that the other two methods don't have, which is out of the limits of water quality and has excellent accuracy.Experimental results showed that tannic acid is stable in low temperature. Under the condition of strong acid which is close to the zeropoint of charge of tannic acid, it has unsatisfied colloidal stability. Under the condition of weak acid, polymerization has the advantage over hydrosis and the bridge effect of polymerized molecular leads to evident elimination of colloid stability, while under the condition of strong alkaline, oxidation is to be important factor which influence the colloidal stability of tannic acid. Gallic acid is detected in tannic acid solution with HPLC, which indicates hydrolysis happens. Hydrolysis is evident for tannic acid solution with low concentration. With the increasing of concentration hydrolysis decreases and polymerization is enhanced. There are three obvious peaks in Gel permeation chromatography (GPC) of tannic acid which maybe stand for polymers and products of completely hydrolysis or partial hydrolysis.After complexation with metal ions, coplanarity of atoms and group in tannic acid molecular increases, which lead to the increase of absorbance of maximal ultraviolet absorption peak and the reshift of maximal absorbtion wavelength. In the FTIR of complexation of tannic acid, strenching vibration at wave-number 1285/1270 cm-1 and increase of absorbance of the peak indicate phenolic hydroxyl participation of complexation reaction.The effect of complexation on the haloacetic acids formation potential (HAAFP) and the trihalomethanes formation potential (THMFP) of tannic acid is studied. In general, complexation promotes the HAAFP and inhibits the THMFP.The ozone mainly attacks three sites of tannic acid: carbon-carbon double bond, aromatic structure and hapto. Ozonation can reduce aromaticity greatly and increase amount of attracting electron group. The decrease of HAAFP may be closely related with decrease of phenolic hydroxyl due to ozonation. After ozonation of tannic acid for short time, a large amount of aldehydes and alkones are produced,which is relevant to the increase of THMFP.The production of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA)increases greatly in the condition of complexation before ozonation compared to the condition of complexation after ozonation. This phenomenon illuminates the complexation cause redistribution of electron density of aromatic structure in tannic acid and so the aromatic structure is easier to be attacked by electrophilic reagent such as ozone.
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