An integrated membrane distillation, photocatalysis and polyelectrolyte-enhanced ultrafiltration process for arsenic remediation at point-of-use

Arsenic contamination of drinking water is a result of natural and/or anthropogenic activities, causing undesirable detrimental effects on the environment and the human health. Herein, an integrated process based on Membrane Distillation (MD), photocatalysis and Polymer-enhanced Ultrafiltration (PEUF) was developed for an effective remediation of arsenic (As). This approach, whose effectiveness was demonstrated by experimental tests on artificial solution mimicking As-contaminated water in the area of Sila Massif (Italy), ensured a near total water recovery and a rational management of residual contaminants. MD allowed to produce high-quality freshwater from contaminated feedwater containing As in the range of 0.059-5 mg⋅L-1, without deterioration of the transmembrane flux up to a recovery factor of 98.8%. Furthermore, a photocatalytic step was applied on MD retentate to convert arsenite As (III) into arsenate As(V), the latter subsequently removed by PEUF with efficiency of 98.2%. Speciation analysis demonstrated the necessity to reduce the feed pH to 5.6 in order to avoid the risk of scaling in MD stage, whereas Na2CO3 softening at pH 9 before the photocatalytic stage ensured both the reactive precipitation of Ca and Mg ions and the depletion of bicarbonate ions.