Degradation of indoor gaseous formaldehyde by hybrid VUV and TiO2/UV processes

This paper presented a new hybrid process of vacuum ultraviolet (VUV) and TiO2/UV for the decomposition of gaseous formaldehyde (HCHO) at a typical indoor concentration level. The performance was assessed by a preliminary technical and economic analysis. Concentration, flow velocity, relative humidity and light intensity were investigated as process variables. The synergistic or combination effect between VUV and TiO2/UV was attained by comparing the experimental conversions with the calculated ones based on the purifier-in-series efficiency model. The results showed that the proposed hybrid process can be technically feasible and economically attractive for the decomposition of gaseous HCHO. The outstanding merit of the hybrid process is the complementation of advantages of VUV and TiO2/UV. VUV improved the conversion of HCHO markedly on the basis of TiO2/UV. Ozone produced by VUV could be decomposed by TiO2/UV and its concentration was less than the maximum recommended by the WHO at the flow velocity of 0.75 m/s or more. There was weak combination effect between VUV and TiO2/UV and the behavior was analyzed in terms of the actions of ozone. The hybrid process was more economical than the TiO2/UV process with a cost reduction of 60% for removing per kg HCHO.