89Understanding Water Quality Parameters
Water quality parameters such as pH, temperature, and alkalinity may dictate effectiveness of the
coagulation-filtration process. The pH during coagulation has a profound influence on the
effectiveness during the destabilization process. The pH controls both the speciation of the
coagulant as well as its solubility, and it also affects the speciation of the contaminants. For high
alkalinity water, an excessive amount of coagulant may be required to lower the pH to the optimal
pH ranges (alum pH 6 to 7, iron 5.5 to 6.5). Temperature also impacts the coagulation process
because it affects the viscosity of the water. Thus lower temperature waters can decrease the
hydrolysis and precipitation kinetics. For some treatment objectives, other parameters like iron,
manganese or sulfate impact coagulation.