Paradee Chuaybamroong

Efficacy of photocatalytic HEPA filter on microorganism removal

UNLABELLED This study assessed the application of photocatalytic oxidation (PCO) to the high efficiency particulate air (HEPA) filter for disinfection of airborne microorganisms. Experiments were conducted at two TiO2 loadings (1870 +/- 169 and 3140 +/- 67 mg/m(2)) on the HEPA filter irradiated with UV-A at the intensity of 0.85 +/- 0.18 or 4.85 +/- 0.09 mW/cm(2) under two relative humidity conditions (45 +/- 5% and 75 +/- 5%). Inactivation and penetration of four microorganisms were tested, including Aspergillus niger, Penicillium citrinum, Staphylococcus epidermidis, and Bacillus subtilis. It was found that microorganisms retained on a photocatalytic filter were inactivated around 60-80% and even 100% for S. epidermidis when the PCO reactions occurred. Lower penetration was also found from the photocatalytic filter for all airborne microorganisms. High humidity decreased photocatalysis efficacy. Increasing TiO2 loading or irradiance intensity did not substantially affect its disinfection capability. PRACTICAL IMPLICATIONS The high efficiency particulate air filter is used widely to remove particulates and microorganisms from the air stream. However, the filter may become a source of microbes if those retained microorganisms proliferate and re-entrain back into the filtered air. This study demonstrates that such a problem can be handled effectively by using photocatalytic reactions to inactivate those confined microorganisms. A 60-100% microbe reduction can be achieved for a wide variety of microorganisms to provide better indoor air quality for hospitals, offices, and domestic applications.

Performance of photocatalytic lamps on reduction of culturable airborne microorganism concentration.

Reduction of viable airborne Staphylococcus epidermidis and Aspergillus niger spore concentrations using two types of photocatalytic fluorescent lamps under controlled environmental conditions (25 vs. 35°C and 55 vs. 75% relative humidity) were investigated. Visible white-light and UVA black light were in-house spray-coated with TiO(2) and then compared with a commercially coated visible white-light for microbial concentration reduction. The white-light photocatalytic lamps reduced the concentration of culturable S. epidermidis up to 92% independent of temperature or humidity change, while the black light photocatalytic lamps completely inactivated the culturable bacteria at 25°C, 55% relative humidity. Humidity seemed to alleviate UVA damage since better bacteria survival was found. For A. niger spores, rising humidity or temperature could lower their concentration or drop their culturabilities so that a difference between the natural decay and photocatalytic disinfection could not be distinguished. Reductions of total bacteria and total fungi concentrations using these lamps were also examined under uncontrolled environmental conditions in an office and a waste-storage room. It was found that photocatalytic lamps could reduce total culturable bacteria concentration from 9 to 97% and total culturable fungi concentration from 3 to 95% within irradiation time of 30-480 min, respectively. Insignificant difference in concentration reduction among these photocatalytic lamps was pronounced.

Effect of binders on airborne microorganism inactivation using TiO2 photocatalytic fluorescent lamps

5% Degussa P25 TiO2 was spray-coated onto black-light and white-light fluorescent lamps, using five different binders, namely DURAMAX B-1000, DURAMAX D-3005, silane-69, and two polyethylene glycols with molecular weight 1000 (PEG-1000) and 700 (PEG-700). The coated lamps were tested with Staphylococcus epidermidis, Escherichia coli, spores of Bacillus subtilis and spores of Aspergillus niger. It was found that 0.5% B-1000 and 1% PEG-1000 gave the highest inactivation rates: 93-96% from coated black-light lamps and 85-88% from coated white-light lamps for bacteria. In the case of spores, 70-72% and 55-57% inactivation rates were recorded from coated black-light and coated white-light lamps, respectively. The effects of UVA irradiance and face velocity were also examined. Significant improvement was observed from coated white-light lamps when the UVA irradiance increased. High face velocity adversely affected microorganism inactivation.

Forest Fire Area Estimation using Support Vector Machine as an Approximator

Forest fire is critical environmental issue that can cause severe damage. Fast detection and accurate estimation of forest fire burned area can help firefighters to effectively control damage. Thus, the purpose of this paper is to apply state of the art data modeling method to estimate the area of forest fire burning using support vector machine (SVM) algorithm as a tool for area approximation. The dataset is real forest fires data from the Montesinho natural park in the northeast region of Portugal. The original dataset comprises of 517 records with 13 attributes. We randomly sample the data 10 times to obtain 10 data-subsets for building estimation models using two kinds of SVM kernel: radial basis function and polynomial function. The obtained models are compared against other proposed techniques to assess performances based on the two measurement metrics: mean absolute error (MAE) and root mean square error (RMSE). The experimental results show that our SVM predictor using polynomial kernel function can precisely estimate forest fire damage area with the MAE and RMSE as low as 6.48 and 7.65, respectively. These errors are less than other techniques reported in the literature.