Arsenic removal from water by coupling photocatalysis and complexation-ultrafiltration processes: A preliminary study

Inorganic As removal from contaminated water has been studied by off-line coupling of photocatalysis and complexation-ultrafiltration (CP-UF), showing that this combination permits to obtain a quite complete arsenic removal from the treated water. Two commercial polymers, poly(dimethylamine-coepichlorohydrin-coethylenediamine) (PDEHED) and poly(diallyl dimethyl amnmonium chloride) (PolyDADMAC) have been tested in the CP-UF process. The operating conditions (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, respectively. The UF tests were performed by continuous diafiltration and diafiltration with volume reduction modes. The latter method permits to save the volume of washing solution during polymer regeneration. As(III) was not complexed, operating under the As(V) complexation conditions, thus a pre-oxidation step by using the photocatalytic approach was carried out to remove As(III) species. As(III) conversion to As(V) was evaluated by As speciation by using the CP-UF process for analytical purposes. Photocatalytic oxidation was successfully performed under UV radiation by using TiO₂ (0.05 mg L^-1), O₂ and pH = 9. The oxidation was very fast during the first 10 min following a zero order kinetics (k = 0.83 mg L^-1 min^-1) and reaching 90% As(III) oxidation. A conceptual scheme coupling photocatalysis and CP-UF and some criteria to operate the CP-UF process, useful to address it towards application, are reported.