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