Question

Problem 5. The aquifer source water used by the town of Pandarwin, IL contains 32 mg/L Fe2+ and 97 µg/L arsenic, predominantly in the form of As(III). To meet the new MCL of 10 µg/L the local water utility is considering several strategies. One strategy involves adding hydrogen peroxide (H2O2) to the water. Arsenic removal occurs indirectly as a byproduct of the reaction between Fe2+ and H2O2. When H2O2 reacts with Fe2+, hydroxyl radical intermediates (•OH) are produced which can rapidly oxidize As(III) to As(V). The As(V) can then be removed by coprecipitation with and adsorption onto Fe(OH)3(s) precipitates during sand filtration. The source water is well buffered at pH 8.0 by dissolved carbonate species.

(a) Write the balanced redox reaction between Fe2+ and H2O2. Fe2+ is converted to Fe(OH)3(s) and H2O2 is converted to H2O.

(b) The treatment plant flow rate is 107 L/day. If we assume that the reaction from part (a) goes to completion as written, calculate the mass of H2O2 that will be required each day to consume all the dissolved Fe2+ in the source water entering the plant.

(c) If we assume that each H2O2 molecule generates a single ⋅OH intermediate when it reacts with Fe2+, estimate the fraction of ⋅OH intermediates that will be used to convert As(III) to As(V) in the source water. Assume that each As(III) molecule reacts with only a single ⋅OH intermediate

Answer 1

Hope it helps.