Preliminary study on As removal from water by coupling photocatalysis and complexation-ultrafiltration processes

The contamination of ground and surface water by As is one of the major environmental problems in the present millennium. As occurs in natural water prevalently in thetrivalent (As (III), arsenite ion), the most dangerous, owing to its higher toxicity andmobility, and pentavalent (As (V), arsenate ion) forms.1 In 2001 the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) set the new Maximum Contaminant Level (MCL) standard for As in drinking water to 10 μg L-1.Conventional technologies for As removal, including coagulation/precipitation and adsorption, present some technological fails and are ineffective for As(III) removal.In the present work the coupling of the photocatalytic oxidation (PO) of As(III) to As(V) and complexation-ultrafiltration (CP-UF) for As removal from contaminated water has been studied.2 In the CP-UF step two commercial polymers,poly(dimethylaminecoepichlorohydrin-coethylenediamine) (PDEHED) and poly(diallyldimethyl amnmonium chloride) (PolyDADMAC) have been tested. The operatingconditions (pH and polymer/As weight ratio) for As(V) complexation were determined finding values of 7.5/20 and 9.2/30 for PDEHED and polyDADMAC, espectively.Thus the type of polymeric agent influences both the considered parameters. As(III) was not complexed operating under these conditions regardless the polymer, confirming theneed of a pre-oxidation process to effectively remove As(III) species from contaminated water. PO of As(III) to As(V) was successfully performed under UV radiation by usingTiO2 (0.05 mg L-1), O2 and pH = 9. The PO was very fast during the first 10 minfollowing a zero order kinetics (k = 0.83 mg L-1 min-1) and reaching 90% As(III) oxidation. A conceptual scheme coupling PO and CP-UF and some criteria to operate the CP-UF process, useful to address it towards application, are reported.