The use of the dynamic light scattering method for characterizing humic acids in natural water

Summary

The results of studying the impact of sodium, calcium and aluminium salts on the dispersive characteristics of humic acids in natural water with the use of Photocor Compact-Z analyzer are presented. The dispersiveness of humic acids by molecular mass determines to wide extent the efficiency of natural water decoloration with aluminium salts. It is shown that the method of dynamic light scattering can be an efficient and rapid method of studying the conformational changes of macromolecules in alkaline and acid solutions, and chemical interactions between humic acids and metal ions. The studies were carried out with natural and simulated water prepared by extracting humic acids from peat with distilled water and blending the obtained solutions to the required color. The ion composition of simulated water was changed by adding calcium chloride, aluminium sulfate, «Aqua-Aurat™30» polyaluminum oxychloride, sodium hydrogen carbonate and hydrochloric acid.

Key words

chromaticity , natural water , aluminium sulphate , aluminium polyoxychloride , humus acids , alkalinity , light scattering

Reducing color of natural water with the use of organic coagulants

Summary

The results of studies of the effectiveness of reducing color of low-turbid natural water by filtration with the use of organic coagulants of domestic trademarks: VPK-402, Kaustamin-15 and Biopag are presented. It is shown that the decrease in color of natural waters with organic coagulants occurs mainly due to coagulation processes at low alkalinity close to zero, and chemical interactions of the polyanion of humic acids with the coagulant polycation with alkalinity more than 1.2 mmol-eq/l. It was determined that the optimal doses of organic coagulants increase with a decrease in molecular weight in the series VPK-402 < Kaustamine-15 < Biopag and an increase in alkalinity of the treated water; whereas with an increase in hardness – decrease. In the alkalinity range of 1.2–2 mmol-eq/l the specific consumption of coagulants VPK-402 and Kaustamin-15 increases from 0.04–0.06 to 0.12 mg per degree of initial color while low-molecular Biopag coagulant practically does not change and is 0.09 mg/degree. The dispersion of the formed particles of the suspension increases with a decrease in the hardness of the treated water, an increase in alkalinity and the concentration of low molecular weight fractions of humic acids in water being purified which is accompanied by an increase in color of the purified filtered water. It is shown that the standard decrease in water color below 20 degrees is achieved by removing coagulated particles with a size of more than 0.3 microns in the process of filtration.

Key words

turbidity , chromaticity , coagulation , natural water , filtration , hardness , alkalinity , organic coagulants

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Chemical aspects of decoloration of low turbidity natural water with aluminium salts

Summary

The mechanism of decoloration of natural water with aluminium sulfate aluminium polyoxychloride is considered. The complexing reactions of humus acids with aluminium salts mainly contribute to the decoloration of natural water. The parallel proceeding reaction of aluminium sulfate and polyoxychloride hydrolysis facilitates the reduction of aluminium ion concentration in treated water but does not reduce color. Empirical dependences of coagulant dosages on color and alkalinity of raw water have been determined. Higher efficiency and lower dosages of aluminium polyoxychloride compared to aluminium sulfate used for decoloration are stipulated by the polymer origin of aluminium polyoxychloride. The use of coagulants in combination with cationic Praestol 650 flocculant provides for improving the efficiency of decoloration by 10–20% at the optimal coagulant: flocculant ratio of 50:1 for aluminium polyoxychloride and 20:1 for aluminium sulfate.

Key words

chromaticity , natural water , aluminium sulphate , cationic flocculant , aluminium polyoxychloride , humus acids , alkalinity , hydrolysis , complexing