Breakup and strength of polystyrene latex flocs subjected to a converging flow

Abstract

Breakup of flocs (aggregates of colloidal particles) in converging flows is encountered in many industrial processes such as filtration, pipetting for sampling of flocs, and mechanical dispersion. The experiment of breakup of flocs by a converging flow opens the possibility to obtain the strength of floc against breakup. The quantity is crucial for controlling flocculator in water treatments and predicting transport of colloidal particles in aqueous environments. Therefore, the mechanism of disaggregation of flocs subjected to a converging flow is emerging as an interesting theme from engineering and scientific points of view. Recently, Blaser evaluated the hydrodynamic disrupting force on a floc in an axisymmetrical straining flow. In the present study, to confirm the validity of the ellipsoidal model proposed by Blaser and to obtain the strength of latex flocs in a simple electrolyte solution, polystyrene sulfate latex (PSL) flocs formed in a simple KCl solution were disrupted by a converging flow of the solution. Experimental data of relationships between floc size and volumetric flow rate were analyzed by assuming flocs hydrodynamically behave like solid ellipsoids to evaluate strength of flocs. The obtained floc strength was 2 nN in average and did not depend on floc size. When the values of floc strength of this study were compared with those of previous researches, they were found to be 1-2 orders smaller than strengths of flocs formed by the addition of polymer flocculants and/or precipitated ferric or aluminum hydroxide coagulants evaluated by similar methods. This result is reasonable because flocculants and coagulants are usually used to increase floc strength in water and wastewater treatments. The value of obtained floc strength was also comparable to the pull-off force between latex particles in water by means of colloid probe atomic force microscopy (AFM) by Hodges et al. However, the obtained floc strength was 1-2 orders of magnitude smaller than the pull-off force between latex particles as found with colloid probe AFM by Li et al.

Postfragmentation density function for bacterial aggregates in laminar flow

“…[8, 9, 12] and validated in Refs. [15, 16]. To find a hydrodynamically equivalent ellipsoid, we use principle components analysis (PCA) on the spatial data for centers of mass of the bacteria in the floc.…”

“…Direct observation of the fragmentation process is challenging, though it has been visualized for flocs in extensional [8–11] swirling and contraction [12] flows. Various strategies have also been proposed to infer floc strength indirectly including microscale cantilever beams [13], atomic force microscopy [14], and traditional particle sizer techniques [15, 16] (augmented by modeling).…”

Measuring Floc Structural Characteristics

“…Computer software is required for the image processing and analysis and a variety of commercial products are available. Image analysis is often combined with microscopy by mounting a CCD camera onto the microscope (Li and Ganczarczyk, 1986;Cousin and Ganczarczyk, 1998;da Motta et al, 2001;Kobayashi, 2004). The advent of photography and image analysis has allowed much quicker measurements of an almost inexhaustible number of different floc size measurements to be made from floc samples when compared to traditional microscope methods (Wang and Gregory, 2002).…”

Hydrodynamic Treatment of Wastewater Effluent Flocs for Improved Disinfection

“…This relationship was later supported by simulation work of Higashitani and Imura (1998). Several authors have observed the break up of floes when flowing through sudden restrietions or other types of eonverging flows (Blaser 2000a(Blaser , 2000bJames et al, 2003;Kobayashi, 2004,). Patil and Pandit (2007) estimated that the energy dissipated per kg of solids disrupted was four orders of magnitude lower for hydrodynamic treatment as compared to ultrasound for the creation of nano-suspensions.…”

“…Previous work in this area either focused on very high pressures (He, 2009), focused on very small scales, or did not address the complex floe structure unique to secondary wastewater effluents (Blaser 2000a(Blaser , 2000bJames et al, 2003;Kao and Mason, 1975;Kobayashi, 2004). This study addresses the mechanism of secondary effluent floe disruption, under conditions of relatively low pressure using a bench-scale apparatus.…”