AWWA JAW60491

Minimizing aluminum residuals in plants using alum-based coagulants can help to minimize the potential of aluminum postprecipitation in the distribution system. Reducing precipitation potential can help to minimize the financial and public health risks associated with the formation of precipitates in water transmission and distribution systems. This article examines the ability of orthophosphate, which is known to interact with aluminum at concentrations commonly found in drinking water, to reduce soluble aluminum levels through the coagulation/ flocculation/separation process. An alternative use for orthophosphate as an aluminum control method is proposed. In bench-scale tests, orthophosphate addition during rapid mix showed the consistent ability to reduce residual aluminum concentration when using alum as a coagulant. Adding orthophosphate in bench-scale tests reduced residual dissolved aluminum concentrations by as much as 350 µg/L. The effect of orthophosphate addition varied with dose, pH, temperature, and chemical addition sequence. Includes 25 references, tables, figures.