Remediation of organic and inorganic arsenic contaminated groundwater using a nanocrystalline TiO ₂-based adsorbent

A nanocrystalline TiO ₂-based adsorbent was evaluated for the simultaneous removal of As(V), As(III), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in contaminated groundwater. Batch experimental results show that As adsorption followed pseudo-second order rate kinetics. The competitive adsorption was described with the charge distribution multi-site surface complexation model (CD-MUSIC). The groundwater containing an average of 329 μg L ^-1 As(III), 246 μg L ^-1 As(V), 151 μg L ^-1 MMA, and 202 μg L ^-1 DMA was continuously passed through a TiO ₂ filter at an empty bed contact time of 6 min for 4 months. Approximately 11 000, 14 000, and 9900 bed volumes of water had been treated before the As(III), As(V), and MMA concentration in the effluent increased to 10 μg L ^-1. However, very little DMA was removed. The EXAFS results demonstrate the existence of a bidentate binuclear As(V) surface complex on spent adsorbent, indicating the oxidation of adsorbed As(III).