Combined Use of Photochemical Reaction and Activated Alumina for the Oxidation and Removal of Arsenic(III)

In this study, a combined approach using photochemical oxidation and activated alumina (AA) was examined as a treatment technology for dissolved As(III). Laboratory-scale As(III) oxidation experiments using photo-Fenton or UV/TiO2 technigues were conducted, and the removal efficiency of total arsenic [As(III)+As(V)] was measured in the presence of AA. In the photo-Fenton oxidation experiments of As(III), the efficiency at pH 3 was higher than those at other pH values (7 and 11). The presence of an excess OH-scavenger was able to slow down the oxidation rate of As(III) at pH 3, whereas its effect was not significant at other pH values. The effects of Fe(III) and H2O2 were also tested by varying their concentrations; increasing the Fe(III) or H2O2 concentration was advantageous for accelerating the oxidation rate of As(III). In the case of UV/TiO2 experiments, the yield of As(V) from the oxidation of As(111) was higher at pH 7 than at pH 3. Not only powder suspensions but also a thin film of TiO2 was effective at oxidizing As(III). Additional experiments were conducted using a real natural water sample; the results implied that both photo-Fenton and UV/TiO2 processes could be viable methods for the oxidation of As(III), both in acid mine drainages (ANMs) and in groundwaters. After a pre-oxidation step for As(III), chemical coagulation with Fe(III) or Al(III) salt should be applied to decrease the total arsenic concentration to below an acceptable level. However, this approach often requires a large amount of coagulant, which is not a desirable factor from the viewpoint of providing a drinking water supply. Hence, the addition of an appropriate adsorbent is likely to be helpful in the oxidation processes of As(III). We have tested AA as an adsorbent for arsenic, and found that the combined use of photochemical oxidation (photo-Fenton or UV/TiO2) and AA can be an effective and practical treatment strategy for high levels of As(111).