The Effects of Aluminium- and Ferric-Based Chemical Phosphorus Removal on Activated Sludge Digestibility and Dewaterability

Peter Ojo, Augustine Ifelebuegu

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
20 Downloads (Pure)


The uses of Al 3+ and Fe 3+ salts in chemical phosphorus removal (CPR) in activated sludge plants have increased considerably in recent years and their full impacts on downstream processes such as dewaterability and digestibility are not fully understood. In this research, the effects of CPR on sludge digestibility and dewaterability were investigated in laboratory-scale experiments using sludge samples from a full-scale wastewater treatment plant. The results of the digestibility tests showed a 21% and 36% reduction in the biogas volume generated during anaerobic digestion of surplus activated sludge at 0.1 g/L doses of Al 3+ and Fe 3+ salts, respectively. This demonstrates that Al 3+ dosing for CPR has less of a reduction effect compared with Fe 3+ salts on biogas generation during anaerobic digestion of sludge. The dewaterability tests showed that primary sludge dewaterability was improved by up to 25% by Fe 3+ and 16% by Al 3+, while that of surplus activated sludge was reduced by 64% and 73%, respectively, at a metal salt dose of 50 mg/L. Consequently, a pre-precipitation process during CPR where phosphorus is removed in the primary tank would, therefore, enhance sludge dewaterability.

Original languageEnglish
Article number228
Number of pages9
Issue number4
Publication statusPublished - 23 Apr 2019

Bibliographical note

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (


  • Activated sludge
  • Anaerobic digestion
  • Biogas
  • Capillary suction time
  • Metal salts
  • Surplus activated sludge

ASJC Scopus subject areas

  • Bioengineering
  • Chemical Engineering (miscellaneous)
  • Process Chemistry and Technology


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