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The Impact of Aluminium Salt Dosing for Chemical Phosphorus Removal on the Settleability of Activated Sludge

School of Energy, Construction and Environment, Coventry University, Coventry CV1 5FB, UK
Author to whom correspondence should be addressed.
Environments 2018, 5(8), 88;
Received: 16 June 2018 / Revised: 24 July 2018 / Accepted: 25 July 2018 / Published: 29 July 2018
PDF [2742 KB, uploaded 2 August 2018]


The use of metal salts like aluminium in the precipitation of phosphorus in activated sludge plants has increased considerably in recent years due to the need to achieve tighter discharge consents for phosphorus in treated wastewater effluent. The impact of aluminium salt (Al3+) dosing on the settleability of activated sludge as a function of zone settling velocity (ZSV) and stirred specific volume index (SSVI) were investigated in batch settleability tests over a three-year period. The results showed that ZSV increased with increasing dose of aluminium salt as SSVI decreased. This trend was observed for dosing concentrations of less than 100 mg/L. At a dose concentration >100 mg/L, the trend was reversed as ZSV decreased and SSVI increased. At dose concentrations of <100 mg/L, Al3+ helped in the bioaggregation of dispersed activated sludge flocs, thereby improving settleability. The surface morphology from the scanning electron microscope (SEM) images indicated that the initial potential of interfloc bridging, open floc formation, and spindly bulking noticed in the undosed activated sludge flocs were remarkably reduced as the flocs became more compacted after Al3+ treatment. At >100 mg/L of Al3+, the sludge settleability started to disintegrate due mainly to surface charge reversal linked to the formation of aluminium hydroxides and the resultant disintegration of the activated sludge floc structure. View Full-Text
Keywords: activated sludge; aluminium; settleability; SSVI; ZSV activated sludge; aluminium; settleability; SSVI; ZSV

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Ojo, P.; Ifelebuegu, A.O. The Impact of Aluminium Salt Dosing for Chemical Phosphorus Removal on the Settleability of Activated Sludge. Environments 2018, 5, 88.

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