Optimisation of arsenate removal from water by an integrated ion-exchange membrane process coupled with Fe co-precipitation

The present work investigates the performance of an ion-exchange membrane process for arsenate removal, consisting in integrating Donnan dialytic transport of arsenic with its simultaneous precipitation in a separate receiver compartment. The process performance was improved by adding a bicarbonate-carbonate buffer in the receiver solution, where iron (III) chloride was used to precipitate the arsenic. This system allowed to maintain the treated water pH within the acceptable drinking water range of 6–9, without further control. A Response Surface Methodology (RSM) was used to infer about the effect of the supply water characteristics (initial arsenic concentration and pH) and operating conditions (mass ratio of iron to arsenic) on the degree of arsenic removal. It was found that the initial pH of the receiver solution was also a required input to predict accurately the arsenic concentration in the treated water (for a predefined treatment time). The model developed has a fitting R² value of 0.99 and a prediction error of 6.6 µg/L of As. The methodology presented permits to develop a simple decision tool (either through the use of equations or visual plots) to determine the effective amount of iron to be used in the treatment of As contaminated water.