Mathematical modelling and analysis of the flocculation process in low retention time hydraulic flocculators

Danieli Soares De Oliveira,Clainer Bravin Donadel

doi:10.4314/wsa.v45i1.01

Abstract

This article aims to advance the understanding of particle interactions in low retention time flocculators and proposes a new flocculation model that appropriately considers the influence of retention time in flocculation processes. This consideration is important for units with flocculation time lower than 1 min, as seen in helically coiled tube flocculators (HCTFs), whose retention time is significantly lower than conventional flocculation units (about 30 min). With this, it was possible to obtain a more adherent model, reducing deviations between results obtained by physical modelling (using HCTFs, 48 tests) and those obtained with the proposed model, when compared with results obtained using the flocculation models commonly used for this purpose. The decreasing-rising behaviour presented by experimental data for process efficiency versus retention time, not verified in the benchmark models, was satisfactorily addressed by the proposed model. Furthermore, maximum and average absolute percentage deviations obtained using the model proposed in this study were less than or equal to the results obtained with the benchmark models and less for experimental uncertainty (10%). The results obtained indicate that this model can be a useful tool to support the rational design of low retention time units, including applications for the water industry and water recycling systems.

Highlights

Clarification is an important stage in the physical-chemical water and wastewater treatment process and has great theoretical and practical importance, including applications for the water industry and water recycling systems, using chemical and/or bioflocculants (Khannous et al, 2011; Ugbenyen and Okoh, 2014; Maceda-Veiga et al, 2015; Mudhiriza et al, 2015; Agunbiade et al, 2016; Ma et al, 2017; Shaikh et al, 2017; Watanabe, 2017)
This paper proposes a flocculation model that appropriately considers the influence of retention time in the flocculation process to obtain a more adherent model when applied to low retention time units
24 helically coiled tube flocculators (HCTFs) configurations were tested and their characteristics are described in Table 1, where d is the tube diameter, D is the curvature diameter, p is the distance between consecutive passes divided by 2π and L is the HCTF length

Summary

Introduction

Clarification is an important stage in the physical-chemical water and wastewater treatment process and has great theoretical and practical importance, including applications for the water industry and water recycling systems, using chemical and/or bioflocculants (Khannous et al, 2011; Ugbenyen and Okoh, 2014; Maceda-Veiga et al, 2015; Mudhiriza et al, 2015; Agunbiade et al, 2016; Ma et al, 2017; Shaikh et al, 2017; Watanabe, 2017). It is fully dependent on the interaction between suspended particles present in fluids, since this interaction promotes floc formation and breakup. In interaction by differential sedimentation, discrete particles with different features (for instance: porosity, density, size and shape) have different sedimentation velocities, leading to collisions between particles moving with different velocities

Objectives

Methods

Findings

Conclusion