The influence of hydraulic loads on depth filtration

The influence of hydraulic loads on the detachment of particles from the collector surface or from previously retained particles was observed in a packed glass beads column. A hydraulic shock load (i.e., 20% increase of flow rate) was applied after 4 h of particle attachment at a constant flow rate. A single type of particle suspension (Min-U-Sil 5, nearly pure SiO2) and three different chemical conditions (pH control, alum and polymer destabilization) were utilized. The magnitude of particle detachment increased with increasing particle size for non-Brownian particles because more shear force was applied to large particles due to their large surface area. More favorable particles (i.e., particles with small surface charge) were detached to a lesser extent than unfavorable particles during the hydraulic shock loads application. This phenomenon can be caused by floc strength. In some cases, when the zeta potential of influent particles was relatively high, the magnitude of detachment of bigger particles (e.g., 4.0-5.0 mu m) was less than that of smaller particles (e.g., 3.0-4.0 mu m). This can be attributable to the breakup of detached flocs as an individual particle. It was also found that the shape of the curve relating the magnitude of particle detachment and particle size can be concave, linear, or convex depending on physicochemical conditions such as floc strength. (C) 2011 Elsevier Ltd. All rights reserved.