Shogo Taniguchi

The usefulness of ultraviolet-C (UVC: 254nm) and vacuum UV (VUV: 185+ 254nm) photolysis for elimination and mineralization of four selected pharmaceutical compounds (PhCs) in mixed aqueous solution were tested in laboratory batch experiments. UVC photolysis was unable to eliminate moderate and refractory PhCs. Moreover, it was not at all useful for mineralization of the PhCs (<10% TOC removal, 30min reaction) and longer reaction period (i.e. 60min) had no significant positive impact on the mineralization efficiency. On the other hand, VUV photolysis eliminated the PhCs almost completely in a short reaction period irrespective of their nature, and 90% mineralization was achieved in an hour. The greatly enhanced elimination and mineralization efficiencies for VUV photolysis were attributed to accelerated direct and indirect photolysis reactions. Based on the results, it was concluded that VUV photolysis was very promising over UVC photolysis for mineralization of PhCs in mixed aqueous solution. However, more studies are necessary for practical applicability of the method in wastewater treatments.

© 2015 The Surface Science Society of Japan. We have conducted a pilot study of a biological filtration (BF) system for low-cost arsenic (As) removal from groundwater containing both ferrous iron (Fe(II)) and arsenic (As). Throughout the study, we have observed that arsenite (As(III)) as well as arsenate (As(V)) could be removed with this system. In conventional water treatment technologies, the preoxidation of As(III) to As(V) by oxidizing chemical is a mandatory step for As(III) removal However, such a preoxidation unit has not been used in our BF pilot unit, and hence the mechanisms of As(III) removal by BF have been of interest. Using a flow-through column reactor that simulates the actual BF pond for analysis by X-ray absorption spectroscopy (XAS), we could observe the adsorption of As(III) in water onto iron hydroxides deposited on the biological filter. The time-resolved As K-edge X-ray absorption near-edge structure (XANES) spectra were obtained when the water containing As(III) and Fe(II) was continuously fed to the reactor. An increase in the absorption intensity of the X-ray with time was clearly observed in the time-resolved spectra, indicating that the spectra represented the concentration and chemical state of As adsorbed at the solid-liquid interface of the biological filter. The XAS results also show that while the original water fed to the reactor was supposed to contain only As(III) and Fe(II), a small portion of As(III) was oxidized to As(V) in the influent line when the As(III) solution met the Fe(II) solution before flowing into the reactor. Consequently, besides As(III), As(V) probably formed by the oxidation of As(III) in the influent, was detected on the filter by XAS. The results demonstrate that, in BF, mechanisms of As(III) removal are at least partially explained by the adsorption of As(III) in the raw water to the biological filter as it is.