Chemistry and fate of Al(III) in treated drinking water

In order to better understand the processes that affect the chemistry and transport of residual Al, solutions were monitored prior to and following water treatment. The use of alum increased the total Al concentration from 0.37 ± 0.33 μmol · L⁻¹ in raw water to 1.8 ± 0.33 μmol · L⁻¹ in filtered water. Approximately 11% of the Al input (raw water and alum) was not retained during treatment, and this residual Al was conservatively transported throughout the distribution system. The treated water contained only a small amount (0.26 ± 0.26 μmol · L⁻¹) of particulate Al. Of the remaining Al (1.5 ± 0.33 μmol · L⁻¹), 29% was associated with organic matter (0.44 ± 0.30 μmol · L⁻¹), 52% was present as monomeric alumino-hydroxide complexes (0.81 ± 0.37 μmol · L⁻¹), and 19% was complexed with F (0.30 ± 0.15 μmol · L⁻¹). Results indicate that chemical addition associated with water treatment (e.g., fluoridation, H₂SO₄ addition) and seasonal variations in water temperature were largely responsible for changes in the speciation of Al.