"Arsenic removal from water employing UV radiation and granular titanium Dioxide: Batch experiences?

MAIA LESCANO; CRISTINA ZALAZAR; RODOLFO BRANDI

San Diego

Congreso; 20th International Conference on Advanced Oxidation Technologies for Treatment of Water, Air and Soil (AOTs-20); 2014

Arsenic pollution is a worldwide problem being one of the most important environmental issues in last years and has been extensively reported by literature. Arsenic in water usually occurs in its two inorganic forms, As (III) and As (V) depending on the prevalent redox conditions, being As (III) more toxic in biological systems than As (V). There are many technologies to oxidize arsenic in water either by traditional oxidants such as Cl2, ClNH2, ClO2, H2O2, KMnO4 or advanced oxidation technologies (AOTs) such as UV /TiO2, UV/H2O2, UV/Fe (III)/H2O2. The AOTs are more convenient because they do not generate undesirable or by-products. In a previous work the efficiency and kinetics of the UV/H2O2 process for arsenic oxidation was evaluated obtaining satisfactory results. Then, the adsorption process was studied because of its simple operation and relative low cost for arsenic removal. The results showed that the granular titanium dioxide (TiO2) is a good adsorbent material for arsenic removal. Furthermore, titanium dioxide is well-known as a photocatalyst. Therefore, the main objective of this work is to evaluate and study the effectiveness of a commercial granular titanium dioxide in combination with UV radiation for arsenic removal from water. In this way, the advantage of the mentioned technology is that arsenic removal will be produced in one step through the oxidation of As (III) by UV/TiO2 and its adsorption onto granular titanium dioxide. Due to this fact, the study of both phenomena (oxidation and As (III)/As (V) adsorption) will be very important in order to understand the process. The experiences were carried out in a batch system at room temperature using a similar system as a Jar Test with 7 beakers (500 mL) but employing a germicidal UVC lamp (ʎ= 254 nm) placed at the top of the equipment. Arsenic solutions were prepared by varying the concentration ratio of As (III) / As (V) (25/175, 50/150, 100/100, 200/0) at the same total arsenic concentration (200 µg/L) and different weight of adsorbent were added to each beaker at three levels: 0.1 g/L, 0.01 g/L and 0.001 g/L. The mixing speed was set at 140 rpm. The employed commercial TiO2 was characterized by different techniques (DRX, XPS, Raman, IR). Preliminary results have shown that the granular titanium dioxide has good photocatalytic activity for all the suspensions tested and that is possible to isolate oxidation from adsorption in the process. These results are in concordance with the information obtained from different solid characterization techniques that have shown the presence of the crystalline form anatase (80%) in the commercial titanium based material. It can be concluded that this study enables to carry out both operations in the same system.