Experimental and numerical characterization of floc morphology: role of changing hydraulic retention time under flocculation mechanisms

Abstract

The formation, breakage, and re-growth of flocs were investigated by using modified flocculation tests and numerical simulation to explore the evolution of floc morphology for different hydraulic retention times. The shorter the aggregation time was, the smaller the flocs produced for the same hydraulic conditions were. Another interesting discovery was that broken flocs that formed in shorter aggregation time had the capacity to completely recover, whereas those formed in a longer amount of time had rather worse reversibility of broken flocs. With the addition of the maximum motion step in the representative two-dimensional diffusion-limited aggregation (DLA) model, there was a transition for flocs from isotropic to anisotropic as the maximum motion step increased. The strength of flocs was mainly affected by the distribution of particles near the aggregated core rather than distant particles. A simplified breakage model, which found that broken flocs provided more chances for diffused particles to access the inner parts of flocs and to be uniformly packed around the aggregated core, was first proposed. Moreover, an important result showed that the floc fragments formed with a larger value of the maximum motion step had more growing sites than did those with a smaller msa value, which was a benefit of following the re-forming procedure.

Magnetic seeding coagulation: Effect of Al species and magnetic particles on coagulation efficiency, residual Al, and floc properties

“…6a and Table 1). In the TC process, D f values slightly decreased for AlCl 3 , Al 13 , and Al 30 after flocs breakage and regrowth, which was attributed to the broken flocs with fewer potential connection points and more open structures for regrowth than the initial floc growth (Nan et al, 2016).…”

“…Al-based coagulants are the most widely used materials in the coagulation process and the distribution of hydrolyzed Al species is generally recognized to be vital for the coagulation behavior (Yang et al, 2010;Hu et al, 2012). The hydrolyzed Al species can be divided into monomeric species (Al a ), intermediate polymer species (Al b ), and higher polymers with colloidal or solid species (Al c ) (Lee et al, 2012;Shirasaki et al, 2016 ), trimer (Al 3 (OH) 4 5þ ) and some small polymers, which normally have small molecular weights (MWs) of <1 kDa, and a high charge per Al (Yan et al, 2007). Al b has represented polymers with MWs in the range of 1 kDae3 kDa, and Al c represents large polymers with MWs larger than 3 kDa (Duan et al, 2014).…”

Hydrodynamic Shear-Induced Densification of Bacteriogenic Iron Oxides: Mechanisms and Implications

“…Morphological measurements of bacterial-mineral materials have been previously used as a method of confirming alterations and structural breakage in response to variable hydrodynamic conditions [37,50,51]. In this study, they are employed as an alternative lens on the effects of aggregate densification intended to complement the experimental microcosm observations, in the manner employed by Ferris et al [24] wherein the effects of hydrodynamic shear on bacterial sheaths were interrogated with samples of BIOS collected from the same location (albeit with different operating conditions of applied shear stress).…”

Understanding the Efficiency of Aluminum Coagulants Used in Dissolved Air Flotation (DAF)

“…There are many studies analyzing flocculation with aluminum salts, some of them analyzing floc strength under different shear forces (deflocculation studies) and the reversibility of the flocculation after breakage (reflocculation studies). However, these studies usually focus on model suspensions of kaolin (Cheng et al, 2011;Wang et al, 2011), humic acids (Wang et al, 2009), or a combination of both (Yu et al, 2009;Zhao et al, 2010;Yao et al, 2014;Nan et al, 2016;Wang Z. et al, 2017) and only in some cases with drinking waters (Yao et al, 2015;Jiao et al, 2016). However, the study of flocculation mechanisms in industrial wastewaters are very limited.…”