Low-Cost Polymeric Aluminum Coagulant

In contrast to alum, coagulants that contain preformed polymeric aluminum species appear to be more efficient coagulants in cold water than in warm. In a simple, one-step process, a low-cost, preformed polymer, poly-aluminum-hydroxy-sulphate (PAHS), was synthesized from alum and powdered limestone. This adds only 10% to the chemical cost when compared to alum alone. Both a bench scale and a study in a small municipal plant indicated that a lower dosage of PAHS resulted in residual turbidity and aluminum lower than or equal to levels achieved with alum. The cold raw water source was high in color and alkalinity but low in turbidity [<1 nephelometric turbidity units (NTU)]. In the plant turbidities of less than 0.2 NTU were readily achieved by PAHS but were never attainable using alum at any dosage. At effluent turbidities of less than 0.2 NTU, the residual aluminum did not exceed 100 parts per billion aluminum, a recommended upper limit for municipal drinking water supplies in Ontario, Canada, set by the Ontario drinking water objectives (ODWOs) guidelines.