Variabilité temporelle de la qualité organoleptique de l'eau potable issue du fleuve Saint-Laurent : contribution du manganèse et du COT

Abstract

The organoleptic water quality monitoring of Montréal produced by Charles-J. Des Baillets station, taken upstream of the distribution network, showed that, according to its physicochemical parameters, drinking water passes through two successive thermodynamic phases to achieve its calco-carbonic balance. During the first turbulence phase of about 2 days, or «complexation/precipitation» phase, the color, the turbidity, the pH and the alkalinity increase quickly with the redox potential (ORP), while it is noticed a decrease of the content minerals in the water which react along with the TOC by complexation and precipitation. In the second phase or «solubilization/stabilization» phase, with decreasing POR, the majority of complexed components of the water are dissolved, while 8,6 % of organic, 1,5 % of mineral fractions more stable precipitate. Different dissolved Mn concentrations (50, 100, 200 and 400 μg/L) were added to the water under study, simulated as accidental pollution. «Complexation/precipitation» of the metal with the TOC was relatively fast, followed by a stabilization phase, partially reversible leading to steady state over the following days. The percentage of Mn complexed with COD and minerals of the water after 3 days are respectively 65 %, 58 %, 31 % and 26 % for the adds of Mn of 50, 100, 200 et 400 μg/L. The presence of Mn in the water amplifies the phenomenon of sensory disturbance. The Mn added correlates with the phenomenon of «complexation/precipitation». The metal correlation is much stronger than its initial content and residence time are important. During the stabilization phase, an increase in Mn content dissolved was observed as the POR decreases. To anticipate the phenomenon of «complexation/precipitation» that occurs in the drinking water after chloration, reduce the excess of Mn (< 0.05 mg/L) from water, together with the TOC (< 0.5 mg/L) before sending it to the treatment plant, is revealed as a subsequent step before final disinfection.

Date	13 Oct 2015
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Robert Hausler (Supervisor)