Understanding ballasting agent dynamics when recycled in a ballasted flocculation process and impact on performance

Ansell, Cameron (2022) Understanding ballasting agent dynamics when recycled in a ballasted flocculation process and impact on performance. [USQ Project]

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Ballasted flocculation is a process where ballasting agent is added to a conventional flocculation process to increase the density of flocs with the objective to increase settling velocities. With these increased settling velocities it is possible to reduce the footprint of treatment process infrastructure significantly, saving both space and cost of construction.

There is currently limited literature available in relation to the operation and performance of full scale ballasted flocculation processes, particularly where ballasting agent is continually recovered and recycled and how any dynamic behaviour impacts performance. Previously published research has been largely conducted at a laboratory scale where ballasting agent is assumed to be constant in nature.

The objectives of this research were to prove or disprove that ballasting agent properties are dynamic when the ballasting agent is continually recovered and recycled in a full-scale ballasted flocculation process and to apply the known principles of ballasted flocculation documented in previously published research to explain impacts on process performance.

A model was developed in Microsoft Excel to calculate and evaluate coagulation, flocculation and sedimentation processes of the full-scale ballasted flocculation process. Modelling of discrete ballasting agent particle settling velocity was also included. Operating parameters for the full-scale ballasted flocculation process were used as inputs to the model.

The ballasting agent used as stock material to add to the ballasted flocculation process and that found within the process being subject to continuous recycling were both analysed for a range of particle properties. Parameters measured included particle size distribution, d10, d60, coefficient of uniformity, concentration and surface area. For the control period, it was found that ballasting agent within the process featured a distinct absence of particles less than 0.150mm, which is in contrast to the stock material being added to the ballasted flocculation process, which contained a significant portion of particles 0.150mm or less. It was also found that ballasting agent concentration varies both temporally and spatially within the flocculation chamber. It was also found that the particle size distribution is sensitive to flow rates though the full-scale process.
Following ballasting agent analysis, targeted jar testing was undertaken to assist in understanding the impacts on performance which could be expected as a result of the ballasting agent changes that were measured. It was found that for a given ballasting agent concentration by mass, performance would be expected to deteriorate when the particle size distribution is dominated by larger particles. Jar testing also demonstrated that this can be remedied if ballasting agent concentration by mass is increased to attain the same surface are concentration.

This research has contributed to advancing the understanding of ballasting agent dynamics and resulting impacts on performance in a full-scale ballasted flocculation process where ballasting agent is continually recycled.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -)
Supervisors: Trzcinski, Antoine
Qualification: Bachelor of Engineering (Honours) (Environmental)
Date Deposited: 19 Jun 2023 03:22
Last Modified: 20 Jun 2023 01:08
Uncontrolled Keywords: ballasted flocculation; operation; performance
URI: https://sear.unisq.edu.au/id/eprint/51870

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