Low concentration formaldehyde: Potential health effects and treatment technology

VOCs exist widely in both indoor & outdoor environment, and have been known as the most hazardous materials which affect public health and welfare owing to their toxicity potential, carcinogenicity and stability. VOCs are recognized as causative agents of the sick-building syndrome, in which formaldehyde (HCHO) is one of them. HCHO has been classified as a suspected carcinogen. HCHO is known to cause nasal tumors, irritation of the mucous membranes of the eyes and respiratory tract, and skin irritation. Because of the increasing concern on HCHO in the indoor environment, the abatement of HCHO is of significant practical interest at low temperature, especially at room temperature. The conventional technique to remove VOCs is activated-carbon adsorption method, which needs to replace and dispose the adsorbent. The disposal of activated-carbon will cause the next environmental problem. The alternative methods are ozone oxidation method, catalytic combustion method, non-thermal plasma method, etc.. The ozone oxidation and the non-thermal plasma methods involve NOx emission and high initial cost. The catalytic combustion method requires a heat source, hence it is a highly energy-wasting process when VOC concentrations are low. In this chapter, two kinds of HCHO decomposition technology were investigated, that is, photo-catalytic degradation and non-thermal plasma technology. Photo-catalytic degradation of VOCs on UV-illuminated titanium dioxide (TiO2) is proposed as an alternative advanced oxidation process for the purification of water and air. Non-thermal plasma (NTP) has great industrial potential and has been applied to the decomposition of VOCs. At the same time, NTP technology has disadvantages such as low energy efficiency and undesirable byproducts such as NOx. So the combination of NTP with photocatalyst technology was used in our investigation. Nano-structured TiO2, Ag/TiO2 and Ce/TiO2 thin films were prepared by sol-gel method at room temperature and used in the photo-catalyst reactor for HCHO decomposition. The effects of doped Ag/Ce/TiO2, relative humidity, oxygen concentration, initial HCHO concentration, UV light wave length, TiO2 amount on HCHO decomposition were investigated. At the same time, destruction of formaldehyde by means of NaNO2 ferro-electric packed bed dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. The difference among four kinds of NaNO2 ferro-electric reactors was compared in terms of specific energy density (SED), energy yield (EY), and HCHO decomposition. Three kinds of catalysts, that is, TiO2, BaTiO3, or TiO2 & BaTiO3 were tested for HCHO removal. Effect of catalyst carrier, catalysts, and catalyst amount on specific energy density (SED), energy yield (EY) and HCHO removal efficiency were investigated. In addition, the by-products were detected and the mechanism of HCHO degradation was performed.