A New Packed Bed Reactor with Photocatalytic Beads for Water Treatment

A new packed bed reactor has been developed, in which a black-light-blue fluorescent lamp was set in the center of a double tube, and in between the inner and outer tube pohotocatalytic beads of silica-gel supporting titania were packed. Because of the structure, UV irradiation efficiency is improved comparing to an external UV irradiation system with light reflection at the outer surface of the reactor.

Photocatalytic water treatment experiments showed decomposition of p-nitrophenol (PNP) as a test pollutant. The decomposition ratio was a function of hydrodynamic residence time, and it slightly depended on the initial concentration of the reactant. Additionally, when the inner diameter of the outer tube was decreased, the decomposition ratio increased remarkably. From these results, it was suggested that the UV irradiation is so law at the outer belt of the packed bed that the photocatalytic reaction does not satisfactory take place.

To discuss this point of photon utilization in more detail, a 2-box model was developed, which consisted of “light-side” with photocatalytic reaction by UV irradiation at the inner range of the packed bed, and “dark-side” with no reaction at the outer belt. The model showed a good account for the reactor performance.