Characterisation and concentration profile of aluminium during drinking-water treatment

An aluminium(Al) characterisation study was conducted at a surface water treatment plant (Buffalo Pound Water Treatment Plant (BPWTP) in Moose Jaw, Saskatchewan, Canada) to understand better the effect of alum coagulant on various Al fractions. The raw water source for BPWTP is Buffalo Pound Lake water. The Al sources at BPWTP are: • present naturally Al in the raw water and • Al derived due to use of alum as a coagulant. Seasonal evaluations of Al at BPWTP showed that raw lake water total concentrations were highly variable. Suspended (filterable) Al was the predominant species of raw water total Al. Organic-bound or organo-Al complex Al appeared to be the predominant species of dissolved Al in both raw and treated water during the September to November 1997 Al characterisation study. However, during October to December 1998, inorganic Al dominated dissolved Al content. Characterisation of Al at BPWTP showed that the use of (liquid) Al sulphate (alum) did not increase the concentration of total Al levels. This was because: • alum coagulation was practised at pH 7, at which the Al is least soluble • clarifier and filtration units effectively removed particulate Al and • granular activated carbon (GAC) was capable of removing part of the organic dissolved Al. The study showed that BPWTP would be able to comply with the requirement of Health Canada Guideline value (for conventional treatment plants) for Al of less than 100 ?g/ l as total Al. Turbidity and dissolved organic carbon of the raw water influenced the applied alum dose at BPWTP. WaterSA Vol.28(1) 2002: 99-10