Estudo do potencial de formação de trihalometanos na água da Lagoa de Extremoz - RN

Abstract

Trihalomethanes formation potential (THMFP) have been used to evaluate the possibility of disinfection byproduct (DBP) formation by chlorination during the water treatment process. Trihalomethanes (THM) represents the sum of chloroform, dichlorobromomethane, dibromochloromethane and bromoform, and is the main class of DBP formed by the reaction of free residual chlorine and natural organic matter (NOM) present in the source waters. This study evaluates the THMFP on the source water from the Extremoz Pond (Natal-RN, Brazil), which is treated by direct filtration/chlorination process, and the THM concentration in the water distribution network. The research was divided in three phases: a) sample collection and evaluation of physical-chemical characteristics of the source water; b) determination of THMFP by adding a chlorine solution in the source water; and c) sample collection and characterization of treated water in the distribution network. Results indicated the presence on source water of hydrophilic organic matter with the predominance of fulvic acids. The THMFP showed that the source water has a strong potential for organic compounds formation, being latter confirmed by the high levels of THM found in the water distribution network. THM on network varied from 0.39 mg/L to 1.11 mg/L, well above the maximum allowed value by Ministry of Health Ordinance No. 2914/2011, demanding measures to minimize its formation. Among the THM found in both, the THMFP assay and in water distribution network, chloroform represented about 80% of the total THM. Significant correlations were observed between hardness and apparent color with the THMFP in source water attesting that Ca2+ and Mg2+ ions can promote the formation of this class of DBP, and that apparent color can be used as a DBP formation indicator. Although bromoform formation was not identified during the THMFP essays, this THM form was quantified in samples from the distribution network. Therefore an investigation on the presence of bromide throughout the water treatment plant and the network distribution system is necessary. Keywords: Disinfection byproducts. Trihalomethanes formation potential. Natural organic matter. Chlorination.