Due to the pollution of indoor air affecting on human being’s health has be increasingly noted. This research was conducted using the combination of ozone and goethite catalyst which oxidize indoor air contaminants, such as formaldehyde and toluene. In addition, it is our main target to develop a commercialized equipment of air purification system to deal with polluted indoor air quality.
This research is divided into two phases. The first phase is to establish the analytical techniques for better quantifying formaldehyde and toluene concentrations, then use ozone plus goethite catalyst process to develop the best operation conditions as obtained in our lab work. The second phase is to build a pilot- scale equipment employed to determine the useful information for future scaling up. According to the experimental results, it was indicated that 0.25 mole of formaldehyde and 0.06 mole of toluene could be completely consumed by one mole of ozone under the flow rate at 1500 ml/min and ozone retention time at 48 sec. After increasing retention time up to 96 and 144 sec, we found that THC decomposition from the degradation of formaldehyde was not obvious. However, THC removal from the degradation of toluene is rather significant, which indicates the oxidized byproducts from toluene can be effectively attacked by ozone molecules if retention time can be prolonged. Adsorption test was performed by passing those air contaminants through the catalysts bed. It was found that the adsorptive effect of formaldehyde and toluene onto the catalyst was rather minor. The combination of ozone and goethite catalyst can decompose 100% of formaldehyde and 76% of its THC by operating 60 ppm of ozone and 35 g of goethite catalyst at the initial formaldehyde concentration 5±0.2 ppm and relative humidity 72%. Similarly, the removal of toluene was 56% and its THC was 44%. Nevertheless, 19 ppm of ozone was still detected in the offgas. Based on this result, it is very crucial on the further design of pilot-scale system by increasing enough amounts of catalysts to substantially destroy the residual ozone to prevent any potential risk to indoor environment.
Since several volatile chemicals, including formaldehyde, alcohols, and xylene, have been widely used in hospital, the pilot test was chosen to treat the indoor air in the selected medical center in Taichung city. According to our preliminary sampling and analysis, the concentrations of formaldehyde and TVOC were found to be 1.6 and 2.5 ppm, respectively. Without using ozone and goethite catalysts, adjusting different average changes per hour (ach) as operated in the air purification system has no effect on the removal of formaldehyde and TVOC in the hospital. However, it can only remove PM2.5 and PM10 up to 30% due to HEPA filtration. When the treatment system was performed at the following condition as 16 ach/ FeOOH 200g/ O3 2.5 ppm for six hours, formaldehyde has been totally removed and TVOC concentration dropped down to 0.7 ppm, which has complied with the suggestion values regulated by EPA Indoor Air Quality (0.1 ppm of formaldehyde, 3 ppm of TVOC). In the mean time, the residual ozone concentration was detected as 0.08 ppm that also conform the regulations by OSHA.
In our pilot-scale results the health risk has been significantly decreased according to the calculation of residual target indoor pollutants. In addition, the annual expense including electricity and accessory would cost NT$7,633. If comparing with the other air purification systems as used in the market, the efficiency of treating polluted indoor air should be superior with 88.7% TVOC removal and 2.048 m3/min CADR. Therefore, this new-developed purification facility would have the chance to be commercially applied in the future and the improvement of indoor air quality for some specific building could be expected.
