Risk of Residual Aluminum in Treated Waters with Aluminum Sulphate

Abstract

Waters treatment by aluminum sulphate is the most used process in waters treatment to remove unwanted microorganisms. The inorganic coagulants are partially hydrolyzed salts; their dissolution in water depends mainly on this one’s pH. However, aluminum residues may remain after dissolving. In this study, determination of residual aluminum in treated waters is performed by the standard addition method. Treated waters from the treatment station in Skikda’s city contained 210 g / L of residual aluminum for an average dose equal to 40 m /L of aluminum sulphate. The residual aluminum in treated water exceeds WHO standards (200 μg / L), and far from the recommended standards of 100 g / L in all searches. Trials were made with laboratory flocculators under the same conditions. The residual aluminium obtained by the same method, is 182 mg / L, giving 13.33% less than the WHO standards. Another trial was carried out with a dose of 40 mg / L alum. As adjuvant, a bentonite from M'Zila (Algeria) was used with a dose of 3 mg / L. This test helped to reduce the amount of residual aluminum in raw water (20.48%, lower than the recommended standards). In order to investigate the causes of these excess, trials were made with the laboratory flocculators under the same conditions in that station. The residual aluminum obtained by the same standard addition method, is 182 mg / L (giving 13.33% less than the WHO standards). The dry residues were characterized by analysis using a scanning electron microscopy (SEM) and EDX (MEB-EDX) to show the different spectra of the aluminum in the dry residue. The crude bentonite is characterized by the elemental chemical method using X-ray fluorescence.