Behaviourof Aluminium During Water Treatment

ReportNo WSAA 85

November 1994




Recentlythere has been increased concern regarding the effect of aluminium on humanhealth, particularly the effect of low levels of aluminium on renal dialysispatients. The long term effect on humans has also been linked with Alzheimer’sdisease.(10)


In asurvey of aluminium levels in Melbourne tap water, high levels of aluminiumabove the WHO guideline level of 200 mg/L were observedin the alum treated water from Bunyip and Tarago reservoirs. Particularfeatures of these supplies were the low alkalinities of the natural waters andpre-dosing with fluoride before the alum treatment. A study was undertaken todetermine the behaviour of aluminium during water treatment and to obtain a setof operating parameters to minimise aluminium levels in the treated water. Itwas found that alkalinity and fluoride levels greatly affect aluminium levelsin the alum treated water. The presence of about 0.8 mg/L of fluoride, in particular,could markedly cause elevated levels of residual aluminium.


Alspeciation studies were carried out on both the raw and treated water, using achemical separation scheme to isolate various fractions. Graphite furnaceatomic absorption spectrometery with detection limits of 2 mg/L was then used todetermine aluminium in each one. a significant finding of this work was thataluminium was dominated by organically bound aluminium before alum treatmentbut was mostly in inorganic forms after the treatment. In the presence offluoride, the elevated level of aluminium in the treated water was largely in the form of solublecationic fluoro and hydroxy complexes.


Boththe Ion Electrode and Ion Chromatography were used in determining fluoride inthe raw and treated water. It was found that loss of fluoride happened duringalum treatment which was due to absorption of fluoride by the flocs andsignificant amounts of fluoride were found in the flocs.


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