Modelling the effects of ferric salt dosing for chemical phosphorus removal on the settleability of activated sludge

Augustine Ifelebuegu, Peter Ojo

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)
154 Downloads (Pure)


There is a growing utilisation of ferric salts (Fe3+) for precipitation of phosphorus from wastewater due to tighter regulatory limits for wastewater effluent discharge. The effect of Fe3+dosing on activated sludge settleability indicators; zone settling velocity (ZSV) and stirred specific volume index (SSVI) were examined in laboratory-based batch settleability tests over a three years period. The experimental data revealed that ZSV increased with increasing dose of ferric salt as SSVI decreased with the highest changes obtained at a dose rate of 50 mgL-1. Fe3+ facilitated the agglomeration of the activated sludge flocs, thereby improving settleability. At >50 (mgL-1) of Fe3+, there was a slight breakdown in sludge settleability due mainly to surface charge reversals. The modelling of the settleability of ferric sludge in recent wastewater engineering practice for design and improvement purposes is presently based on conventional empirical sludge settleability models. This paper proposed a new activated sludge settleability model that describes the effects of Fe3+ dosing on the ZSV and SSVI of activated sludge. The exponential form of the Vesilind equation was optimised and validated to include ferric chemical dosing parameters. The proposed ferric settleability equations were found to effectively describe the settling characteristics of ferric sludge.
Original languageEnglish
Article number103256
JournalJournal of Environmental Chemical Engineering
Issue number5
Early online date16 Jul 2019
Publication statusPublished - Oct 2019

Bibliographical note

NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Environmental Chemical Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Environmental Chemical Engineering, 7:5, (2019)
DOI: 10.1016/j.jece.2019.103256

© 2019, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International


  • Activated sludge
  • Ferric salt
  • Settleability
  • Stirred sludge volume index
  • Zone settling velocity

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Waste Management and Disposal
  • Pollution
  • Process Chemistry and Technology


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