Effect of Flocculation on Critical Flux during Crossflow Microfiltration of Bentonite Suspensions

Abstract

The effectiveness of polymeric flocculant addition and hydrodynamics on increasing the critical permeation flux, J crit , during crossflow microfiltration of bentonite suspensions using a tubular ceramic membrane module was investigated. The investigation determined the effects of flocculant concentration on J crit at various crossflow velocities. The best filtration performance (highest J crit ) was obtained at a flocculant dose of 500 mg kg -1 (mg of flocculant per kg of solids) and at a crossflow velocity of 1.71 m s -1. Particle size has been used as a parameter to fit the shear-induced hydrodynamic diffusion model to the experimental filtration data.

Improving permeate flux and product transmission in the microfiltration of a bacterial cell suspension by flocculation with cationic polyelectrolytes

“…The reduced benefit is likely due to selective deposition of smaller particles because of greater shear-induced back diffusion of larger particles [18,21,[23][24][25].…”

“…Flocculation has found extensive use in the waste water and biotechnology industries to aid in separation techniques, such as filtration, flotation, sedimentation [16], and centrifugation [17], where rate improves with the size of the suspended particles. Previous studies have shown that the addition of a polyelectrolyte flocculant results in increased permeate flux rates for the crossflow microfiltration of yeast cells [18,19], CHO cell suspensions [20] in simple media, bentonite [21], and titanium oxide in deionized water [22], but microfiltration of a complex media broth has not been examined.…”

A Brief Review of Filtration Studies for Waste Treatment at the Hanford Site

“…A number of studies employ the critical flux, rather than steady-state flux, as a reference flux for the study of filtration parameters (such as crossflow velocity, slurry particle size, or eletrokinetic effects). Examples include Chellappah et al (2008), Chong et al (2008), Kim and Zydney (2006), and Huisman et al (1999b). As stated above, critical flux is related to conditions that lead to the incipient deposition of particles on the filter surface.…”

“…Mixing conditions also impacted the degree of flocculation (and permeate flux improvement). Chellappah et al (2008) presented another flocculation study. This study examined the increase in critical flux (i.e., the flux below which no fouling occurs) observed in crossflow microfiltration of bentonite suspensions upon addition of flocculent.…”

“…Davis and Leighton (1987) and Davis and Sherwood (1990) postulated that particle deposition occurs at some critical distance, x cr , from the entrance to the filter element. Chellappah et al (2008) provide a solution for x cr when back transport from the surface is governed by shear-induced diffusion (see Equation 3.10):…”