Designing thickeners by matching hindered settling and gelled suspension zones in the presence of aggregate densification

Abstract

A model is presented for design of a thickener for solid–liquid separation where the flocs or aggregates within the solid–liquid suspension undergo an aggregate densification process due to the action of rakes. This aggregate densification facilitates suspension dewatering. The novel feature of the model is that it manages to couple together a hindered settling zone (higher up in the thickener, where the flocs are separated from one another, and the suspension cannot bear weight) and a gelled suspension zone (lower down in the thickener, where the flocs are packed together, and the suspension is able to bear weight). The model determines solids fraction profiles throughout the hindered settling zone and the gelled suspension zone, and also gives zone heights and residence times. Parametric investigations using the model are carried out for different suspension fluxes (which influence the solids fluxes and underflow solids fractions attained), and also for different specified amounts of and rates of aggregate densification

Is the dewatering of Palm Oil Mill Effluent (POME) feasible? Effect of temperature on POME’s rheological properties and compressive behavior

“…Zhang et al (2015b) states that the compressive yield stress can exhibit different types of variation in the neighborhood of the gel point, . Zhang et al (2015a) suggested an empirical equation to fit the compressive yield stress Py( ) as shown in equation 1. However, in the present study equation 1was rewritten in such a form that the constants C0, b0 and k0 were collapsed together into a single parameter denoted by X0 ( 0 ≡ 0 / 0 0 ), since compared to Zhang et al (2015b) study, in the case assuming − ≪ 0 some parameters are redundant (Stickland, 2015;Zhang et al, 2015a).…”

Effect of Aluminium Salt Dosing on Activated Sludge Settleability Indicators: A New Settleability Model Development

“…The correlation obtained was expressed in Equation 2. Further research by Ekama and Marias [45] was analysed along with that of other researchers-including Rachwall et al [29], White [36], Koopman and Cadee [46]-and came up with the findings that Pitman's empirical expression in Equation (2) resulted in a good description for all and that a relationship exists between v 0 K and k. This was expressed as in Equation 4…”

“…Since the mass flux theory was developed by Kynch [21] various studies have been conducted [6,7,22,23], to examine the relationship between zone settling velocity (ZSV) and activated sludge concentration (X) and to also evaluate the efficiency of FSTs in an ASP, by a number of empirical models [24][25][26][27][28]. Other empirical settling velocity models were proposed due to different activated sludge settling zones and they find application in forecasting the flow field and velocity of flow and estimating the sludge blanket height [6,12,29]. They include; one-dimensional (1-D) and two-dimensional (2-D) settling models [30][31][32][33].…”

Concentration profiling of a horizontal sedimentation tank utilising a bespoke acoustic backscatter array and CFD simulations

“…The characterisation of large-scale solid-liquid separators is critically important for a range of industries; from water and wastewater treatment to minerals processing and paper production e.g. (Benn et al, 2018;Ramin et al, 2014;Zhang et al, 2015a). Understanding separation changes with variations in feed composition or flow regimes are key concerns, which can lead to significant downstream issues if performance is reduced.…”

“…Such operational issues have led to a large body of work focused on modelling (both analytical and numerical) and hydrodynamic simulation of large-scale operations, including work on primary horizontal or radial settlers, commonly known as clarifiers (Asgharzadeh et al, 2011;Fan et al, 2007;Goula et al, 2008;Shahrokhi et al, 2012;Stamou et al, 1989) and secondary thickeners (Gladman et al, 2010;Guyonvarch et al, 2015;Zhang et al, 2015a). Aspects such as feedwell design and the effect of baffles on turbulence and recirculation have been particular areas of attention e.g.…”