Étude de la performance des filtres Vortisand en présence d’un balayage de surface

Abstract

In water treatment, filtration is facing an important challenge: clogging of the surface. To reduce this problem, cross flow sand filters such as the Vortisand produced by Evoqua use a water velocity parallel to the filter surface. This cross flow is assumed to minimize clogging of the surface. However, the effect of the cross flow on the clogging and filter efficiency remains poorly understood. This thesis presents a study of the influence of cross flow on clogging and filter efficiency for Vortisand filters. Two parameters were varied: cross-flow velocity and particle concentration. A laboratory scale model of a cross flow sand filter was designed and built. Particles of kaolin with a median diameter of 4.6 μm were used to represent impurities. Uniform silica sand with an effective size of 158 μm was used as the filter media. Tests were performed with two kaolin concentrations (250 and 750 mg/L). The cross flow velocity (CFV) was varied from 0 to 35 cm/s. Turbidity, suspended solids and total kaolin measurements were performed on the filtrate. Clogging was appraised from the concentration of kaolin retained in the filter and the head loss during filtration. The size of particles retained throughout the filter was estimated. The results showed that particle retention is influenced by CFV. The influence of cross flow on the deposition efficiency was dependent on the particle concentration. The size of the retained particles is also influenced by CFV. For some CFV (between 7,5 and 13 cm/s for a concentration of 250 ppm, and between 25 and 30 cm/s for a concentration of 750 ppm), particle deposition was improved up to 20 %. However, head loss was also increased. On the other hand, high CFV caused a decrease in both particle retention and head loss.

Date	19 Jan 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Duhaime (Supervisor)