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POLLUTION OF ALGERIAN SURFACE WATER AND THE EFFECT OF COUPLING CHLORINE/POTASSIUM PERMANGANATE

Congress: 2008
Author(s):
Saadia GUERGAZI and Samia ACHOUR Research Laboratory in Subterranean and Surface Hydraulics (LARHYSS) Biskra University, Po Box 145, RP, 07000, Biskra, Algeria Tel. (+213) 33 74 50 90 E-mail : info@larhyss.net

Keyword(s): surface water, organics, mineralization, chlorine, potassium permanganate
AbstractChlorine was first introduced into drinking water in the early 19OOs for protection against water-borne diseases. Since then, it has been the most widely used disinfectant in the world. However, the addition of chlorine to water in the presence of naturally occurring organic matter such as humic and fulvic acids, results in the formation of numerous harmful by-products. Disinfection by-products are potentially toxic and several classes may form including trihalomethanes. In Algeria, humic material can account for 60 to 90% of the total organic carbon in most surface waters used to produce drinking water. In addition, our previous studies showed a high reactivity of these waters during chlorination step and a possible formation of organohalogenated compounds. As more became known about the potential by-products associated with chlorination, the search began for alternate disinfectants such as ozone, chlorine dioxide or potassium permanganate. In water treatment plants, preoxidation with potassium permanganate can maintain an oxidizing environment, control taste/odour, oxidize iron and manganese and assist with the removal of trihalomethane precursors. The aim of this study is to contribute to the knowledge of two powerful oxidants reactivity, namely chlorine and potassium permanganate, towards some Algerian surface waters whose used for drinking water. Trials are conducted out with four surface waters (Beni Haroun, Mexa, An Dalia and Foum El Gherza) under controlled experimental conditions (oxidant dose applied and contact time). In the first stage, the main physico-chemical characteristics of water samples are determined. In the second stage, the study is conducted to determine the effectiveness of a combined use of permanganate oxidation and chlorination as a means of decreasing reactivity waters and chloroform production potential. Residual of chlorine and permanganate is measured by an iodometric or spectrophotometric method and chloroform is analyzed by gas chromatography using a head space technique. In the raw surface waters, the results showed the presence of relatively important amounts of organic compounds, particularly humic substances. Also, the mineralization is often considerable, especially in the south of Algeria. Chlorination of water samples lead to high values of chlorine consumption potentials (from 5,6 to 16,7 mg/l) and a great formation of chloroform. Using high dosage of permanganate pre-treatment, a significant reduction of chlorine consumption and chloroform levels (30 to 50%) was obtained. The results put forward that the permanganate dosage is one of the key parameters in the process of permanganate preoxidation. .For humic substances that serve as precursors of trihalomethanes, permanganate might oxidize these to smaller molecules and leaves fewer of the highly reactive sites. Thus, the chlorine has fewer places to react. For this reason, it usually results in lower demand for chlorine and levels in by-products formation. After preoxidation by KMnO4, final chlorine consumptions decrease at the same time as the aromaticity of organic structures.
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