SPECIATION ANALYSIS AND THE OCCURRENCE OF ALUMINUM TURBIDITY

Abstract

Determinations of particulate Al (pAl), leachable particulate Al (lpAl), and soluble Al (sAl) along the treatment sequence were used to investigate the occurrence of turbidity at drinking-water plants using aluminum coagulation. The behavior of Al species during filtration was normal when sAl remained at a constant level, while pAl was completely eliminated. When sAl was constant while pAl was not completely eliminated, the presence of residual pAl could be attri buted to problems of filtration effectiveness. When sAl decreased during filtration, the residual pAl could also originate from transformations such as precipitation occurring in the filtration media. When sAl increased, the residual pAl could also originate from precipitate detachments. Increases in sAl during filtration or the presence of partially leachable pAl were associated with deteriorations in residual pAl along filtration runs. The presence of nonleachable pAl denoted the existence of different aluminum forms. This was a supplementary indicator of treatment problems and affected the relationship with turbidity. In addition to demonstrating the occurrence of aluminum turbidity, speciation analysis offered a characterization of turbidity and its origin. By contributing to the evidence as well as the understanding of treatment problems, these speciation methodologies can be useful to minimize aluminum turbidity.