AWWA JAW37598

Arsenic removal during coagulation or Fe-Mn oxidation is examined to aid utilities that desire to improve arsenic removal. Fundamental mechanisms of arsenic removal are discussed, optimization strategies are forwarded, and some insights are provided to guide future research. Specifically, As(III) removals by coagulation are primarily controlled by coagulant dose and relatively unaffected by solution pH, whereas the converse is true for As(V). When compared on the basis of moles iron or aluminum hydroxide solid formed during coagulation, iron and aluminum coagulants are of demonstrably equal effectiveness in removing As(V) at pH < 7.5. However, iron based coagulants are advantageous if soluble metal residuals are problematic, if pH is > 7.5, or if raw water contains As(III). Arsenic removal during Fe-Mn oxidation is controlled by the quantity of iron removed [Fe(OH)3 formed] and is relatively independent of the quantity of manganese removed (MnOOh formed). Includes 63 references, tables, figures.