Factors influencing residual aluminium levels at the Buffalo Pound Water Treatment Plant, Saskatchewan, Canada

One of the current concerns for water treatment plants using alum as a coag ulant is elevated concentration of residual aluminium in finished water. Th e objective of the study is to examine the seasonal variations and factors influencing residual aluminium at the Buffalo Pound Water Treatment Plant ( BPWTP). Analysis of BPWTP data for two years related to seasonal variations of total/dissolved aluminium levels showed that much of the raw water tota l aluminium were in particulate form. Raw water particulate aluminium is co rrelated well (r(2) = 0.79 for 1996 and r(2) = 0.82 for 1997) with raw wate r total suspended solids indicating much of the particulate aluminium is de rived from the suspended solids present in raw water. An analysis of eight- year data on total/dissolved aluminium, turbidity, dissolved organic carbon and applied alum dosage showed that dissolved organic carbon present in th e raw water played a major role in controlling efficacy of alum coagulation at BPWTP. The data showed that when alum/DOC ratio is less than 7, insuffi cient alum addition led to incomplete coagulation resulting in colloidal ma terial mostly consisting of organic aluminium in particulate form. Hence pa rticulate aluminium increased in treated water. But this increase in partic ulate aluminium did not increase the turbidity of treated water. This indic ated that an adequate alum dose in response to dissolved organic carbon cha nge is important in minimising residual aluminium in treated water at BPWTP .