Effects of temperature and pH on residual aluminium for alum and polyaluminium coagulants

The effects of temperature and pH on dissolved and particulate Al concentrations are examined using laboratory and field data. The field data include sample collection at five water treatment encompassing a range of raw water characteristics and treatment processes. Al solubility measured by addition of Al coagulants to deionized water is used as a basis for comparison to field data. It is shown that dissolved Al concentrations vary with pH and temperature, but both effects are reasonably well described by the solution pOH. Hydroxyl ion concentration can be considered a complexing ligand for Al that is influenced by pH and temperature. Dissolved Al concentrations are minimized near pOH = 8. Particulate Al is less well understood but is shown to be correlated with treated water turbidity, temperature, and pOH. Particulate Al is minimized if treated water turbidity is below 0.2 NTU. Surprisingly, higher particulate Al is observed in warmer waters.