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1 Polish Journal of Chemical Technology

1 2005

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The use of electrokinetic measurements in a study of pulp wastewater treatment with aluminum and iron (III) salts

Dziejowski J., Libecki B., Smoczyński L.

Polish Journal of Chemical Technology

2005

Vol. 7, nr 1

13-19

Pulp wastewater poses a serious threat to the natural environment. It is characterized by strong coloration and a high content of organic contaminants, including compounds resistant to biochemical decomposition, often toxic to living organisms. Among a variety of physical and chemical methods of wastewater treatment, coagulation is distinguished by its simplicity and efficiency. The effectiveness of the process depends on the pH and the coagulant dose. The optimization of the process parameters can be done based on electrokinetic measurements, including: potential zeta and the streaming potential. This study examined the process of the coagulation of raw effluents from a sulfate pulp mill with aluminum and iron (III) chlorides. A standard jar test method was used. The color, turbidity, suspension and COD were determined in the samples. Tests with and without pH adjustment were conducted. Electrokinetic measurements were performed with a PCD 03 meter (Mütek Analytic Gmbh). It was found that coagulation effectiveness depended on the salts used. A correlation was also observed between the optimum pH for a determined coagulant dose and the reagent-adding sequence. Iron (III) chloride appeared more effective than aluminum chloride as regards the COD elimination. However, taking the lower optimal dose and a higher pH of coagulation into account, aluminum chloride seems to be a better coagulant for pulp wastewater treatment. The increase in the streaming potential recorded during the tests is correlated with the changes in the wastewater pH. The charge of colloids is dependent upon the pH, so different mechanisms of coagulation can be expected.