An estimate of activated‐sludge floc permeability: a novel hydrodynamic approach

Abstract

This work estimates the interior permeability of waste activated sludge flocs by observing the motion of individual flocs moving vertically toward an impermeable flat plate. Through a comparison of experimental data with theoretical predictions in the literature, floc permeabilities of original sludge and freeze–thaw‐conditioned sludges are found to be 0.7 × 10−7 to 5 × 10−7 m2 and 0.9 × 10−9 to 6 × 10−9 m2, respectively. Moreover, incorporating inertial effect delays the influence of the flat plate, thereby causing the creeping‐flow‐based correlation to fail.

Hydrodynamic drag forces on two porous spheres moving along their centerline

“…In addition, the value is strongly a ected by the spheres' separation at ÿ ¿ 1:5. This is the range for typical sludge ocs observed in previous studies (Wu et al, 1998(Wu et al, , 2000a. Fig.…”

“…Over the range 2 ¡ ÿ ¡ 20, the drag force on spheres is sensitive to the oc size and permeability, which are not easily quantitatively evaluated in practice. In applications involving wastewater ocs the corresponding ÿ values range 1.5 -5.0 for the original activated sludge ocs (Wu et al, 1998), and 5.0 -20 for polyelectrolyte occulated sludge ocs (Wu et al, 2000a,b). Restated, the ÿ values of real world ocs locate at the regime where the oc permeability and size considerably a ect the drag force.…”

Advective Flow and Floc Permeability

“…The fluid could "detect" the approach of a floc when the distance between it and the floc falls below a critical value, δ c This critical distance for a porous floc is less than that for an impermeable floc, because of the advection flow (15). Figure 7 presents such a case.…”

“…Wu et al (15) applied a hydrodynamic approach to estimate the permeability of the floc's interior. The basic concept is simple: the response of a porous floc subjected to a (mild) change in its hydrodynamic environment should differ from that of a nonporous object of the same size and weight.…”

Experimental and numerical analysis of the hydrodynamic behaviors of aerobic granules

“…As for sludge flocs, which are highly porous aggregate, 28 the b value is usually very small, ranging from 1.4 to 6.8. 29 However, the b values of aerobic and anaerobic granules generally range from 10 to 10,000.…”