DEPENDENCE OF ALUMINUM IONS UPON PH AND DOSAGE OF COAGULANT-FLOCCULANT IN THE WATER TREATED AT BOVILLE PLANT

In the water treatment plant of Boville, polyaluminium chloride is used as a coagulant-flocculant. Water treatment with polyaluminium chloride causes the increase in the concentration of aluminum anion in water. Aluminum anion concentration in water, according to STASH 3904:1997 and European standard EC 80/778, must be near the value 0.05 mg/ L and with maximum allowed peak of 0.2 mg/ L. Because of the link between aluminum anion exposure and Alzhaimer disease development, and other related health risks, it is necessary that the process of coagulation-flocculation is optimized and dosage of polyaluminium chloride ions (Al 3+) in treated water is kept according to the above values. For the optimization process of water treatment, in laboratory conditions, Jar-test method is implemented. Data collected from the Jar-test shows that the minimal values of aluminum anion concentration were achieved at 7.5 pH. To achieve pH correction and water safety, according to STASH 3904:1998, optimal dosage of hydrochloric acid (30-33%) must be in the interval 12-20 mg/L as the optimal dosage of polyaluminium chloride ranges from 8 to 25 ml/g depending on the turbidity and pH of untreated water.