A rapid treatment of formaldehyde in a highly tight room using a photocatalytic reactor combined with a continuous adsorption and desorption apparatus

A novel air-purification system, consisting of the photocatalytic reactor with a parallel array of blacklight blue fluorescent lamps and the continuous adsorption and desorption apparatus with a cylindrical ceramic-paper honeycomb rotor retaining activated carbon or zeolite fine particles, was constructed and the performance of this system was investigated for treatment of gaseous HCHO at a concentration level of ppbv (< 1 mg m^-3) in a 10 m³ highly tight closed room. With the zeolite rotor, it was very difficult to desorb the adsorbed HCHO by exposing the rotor to heated air and then to photocatalytically decompose the desorbed HCHO. In contrast, the activated carbon rotor provided an excellent performance. With this rotor, the indoor HCHO concentration was reduced to the neighborhood of the WHO guideline (0.1 mg m^-3) in 10 min and to an almost zero value in 90 min. Needless to say, this surprisingly high performance is owing to the cooperative work by the activated carbon rotor to adsorb the indoor HCHO and the photocatalytic reactor to rapidly decompose the HCHO desorbed by heating the rotor. This system offers several other advantages. The adsorption rotor can be used semi-permanently because it is continuously regenerated. In addition, the HCHO adsorbed on the activated carbon rotor is readily released at a desorption temperature of 120°C. Under such a low temperature condition, little loss in the photocatalytic activity was caused.