Predicting Fe3+ dose for As(V) removal at pHs and temperatures commonly encountered in natural waters

Equations describing quantitatively the relation between Fe3+ dose and residual arsenic concentration, Ce, at pH values ranging between 6 and 8 and various initial arsenic concentrations, Co, were established using a natural water spiked with As(V). These equations were used to calculate the specific arsenic removal, q, in μg As removed per mg Fe3+ added. In turn, reliable equations relating q and Ce in the range between 2 and 20 μg As/L were derived. The latter equations predicted Fe3+ dose, necessary to achieve any selected Ce, when the water's Co and pH were known, with a satisfactory degree of accuracy (relative standard deviation less than 15%). In addition, comparison of As(V) removal data from full scale water treatment plants to those predicted by the empirical equations presented in this work, corroborated the fact that these equations can serve as a reliable guide for the prediction of Fe3+ dose necessary to remove As(V) from drinking water. The process of arsenic removal by using Fe3+ as a coagulant was found to be exothermic in character and Ce showed an increase by a factor of about 1.5 for each 10 °C increase in temperature.