Conventional coagulation is not an effective treatment option to remove natural organic matter (NOM) in water with high alkalinity/pH. For this type of water, enhanced coagulation is currently proposed as one of the available treatment options and is implemented by acidifying the raw water and applying increased doses of hydrolyzing
coagulants. Both of these methods have some disadvantages such as increasing the
corrosive tendency of water and increasing cost of treatment. In this paper, an improved version of enhanced coagulation through
coagulant optimization to treat this kind of water is demonstrated. A novel
coagulant, a composite
polyaluminum chloride (HPAC), was developed with both the advantages of
polyaluminum chloride (PACl) and the additive
coagulant aids: PACl contains significant amounts of highly charged and stable polynuclear
aluminum hydrolysis products, which is less affected by the pH of the raw water than traditional
coagulants (
alum and ferric
salts); the additives can enhance both the charge neutralization and bridging abilities of PACl. HPAC exhibited 30% more efficiency than
alum and ferric
salts in
dissolved organic carbon (DOC) removal and was very effective in turbidity removal. This result was confirmed by pilot-scale testing, where particles and organic matter were removed synergistically with HPAC as
coagulant by sequential water treatment steps including pre-ozonation, coagulation, flotation and
sand filtration.