Spin-off dell’Università di Padova
INDOOR CLEAN BREATHING Performance report Verification of ambient air Purification in actual usage conditions Verification of abatement of aero-dispersed PATHOGENS and VOLATILE ORGANIC COMPOUNDS
Product: BKM 3.0 (PATENTED) CONTRACTOR
TEAM R&D
Idrobase Group s.r.l. Via dell'Industria, 25 35010 Borgoricco (PD)
K-INN Tech s.r.l. Via Porciglia, 14 35121 Padova
Padua, 31/08/2021
Index 1.
Objectives .................................................................................................................................................. 3
2.
Description of the technology and the device............................................................................................ 3
3.
Rational design of the device..................................................................................................................... 3
4.
Experimental methods ............................................................................................................................... 4 Abatement of aero-dispersed pathogens ........................................................................................................ 4 VOC abatement ............................................................................................................................................. 5
5.
Results ....................................................................................................................................................... 6 Pathogens abatement ..................................................................................................................................... 6 VOC abatement ............................................................................................................................................. 6 Interpretation of the device’s performances .................................................................................................. 7
6.
References ................................................................................................................................................. 7
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1. Objectives The present document details the design modalities, the experimental testing methods and their results regarding the efficacy of the BKM 3.0 device with respect to the abatement of volatile organic compounds (VOCs) and aero-dispersed pathogens.
2. Description of the technology and the device Product: BKM 3.0 Device description: Air purifier for indoor environments using UV-C radiations to:
directly eliminate aero-dispersed pathogens;
activate a photo-catalyst made of titanium dioxide nanoparticles, which reduces the concentration of volatile organic compounds (VOCs) in the air.
BKM 3.0 products are equipped with 2 UV-C germicidal lamps, emitting at 254 nm, and with a tangential fan with two air velocity settings. Internally, the device has a series of specially shaped surfaces over which the photo-catalyst is finely distributed, which are located in a way to maximize surface illumination by the UV-C lamps. The specific position and geometry of the components as well as the device operation are patented. BKM 3.0 products are ozone-free.
3. Rational design of the device The coupling of photo-catalysis technology with the germicidal effect of UV-C radiations in a single device has been made possible through experimentation on a laboratory scale, which have allowed to validate a complex mathematical model. This model quantifies the relations between the rate of VOCs and pathogens removal, the hydraulic contact time and the local intensity of the UVC radiation. Through this model the current prototype has been designed, for what concerns:
extension of the photo-catalytic surface, in order to increase the abatement of VOCs by the titanium dioxide;
positioning of the lamps, to maximize the distribution of UV-C radiation intensity in every spatial point and on active surfaces, thereby optimizing the velocity of destruction of pathogens and VOCs.
The development phase lasted 10 months and has been conducted with experiments using n-decane, toluene, formaldehyde, trichloroethylene and acetone for what concerns VOCs, and Escherichia Coli for what concerns pathogens. Regarding the latter, the ranking of resistance of microorganisms provided by the Food and Drugs Administration (FDA) has been considered, which identifies bacteria as more resistant to UV-C radiations compared to lipid viruses such as Coronaviruses [1]. page 3
4. Experimental methods The procedure of experimental testing for the device’s performance has been developed in order to evaluate its efficacy in actual usage conditions. This means that the measurements regard the abatement of VOCs and pathogens inside the operating device, based on the difference between the inlet and the outlet concentration. The exposure time is of fractions of a second, as opposed to other more common testing procedures that use far longer times, that are, however, not representative of the actual operation of an air sanitizer.
Abatement of aero-dispersed pathogens
Reference microorganism: Escherichia coli NCTC 9001 (>100000 CFU)
Culture medium: liquid medium Luria Bertani (LB)
Experimental procedure: the outline of the setup is reported in Figure 1. The bacteria are aerosolized and transported via a dedicated aerosol generator, fed with pressurized air. The bioaerosol is mixed with the air drawn by the BKM 3.0’s fan and fed to the device. The humidity content in the air is maintained at a high level in order to guarantee the bacteria’s transport in the aerosol: a second aerosol generator, this one using ultrasounds, feeds a humidified secondary air stream to the mixer, which is proportional to the fan’s flowrate in order to maintain constant humidity inside the device. At the outlet the species are impinged by sampling the air flow and bubbling the stream through a bottle containing 100 ml of sterile water. The bacteria impinged in the bottle are then grown on a sterile Petri dish for a night at 37°C. Two tests are conducted in rapid succession, both lasting 40 minutes: in the first one, the UV-C lamps are off and the aerosolized bacteria are sampled and collected in order to obtain a reference value, in CFU/ml (CUVC OFF). In the second one the UV-C lamps are turned on and with the same method the concentration of surviving bacteria is obtained, in CFU/ml (CUVC ON). The abatement is calculated by the percentage reduction between CUVC ON and CUVC OFF. For every test, two different samplings are conducted, in order to verify its reproducibility.
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Figure 1. Outline of the setup used for the abatement of aero-dispersed pathogens.
VOC abatement
Reference VOC: Acetone
Detector: Flame ionization detector (FID)
Experimental procedure: the outline of the setup is reported in Figure 2. The VOC is fed via a flow of air saturated with acetone, obtained through a bubbler operating at isothermal conditions at 25°C. The flowrate is controlled through a high precision mass flowmeter. This stream is mixed with the air drawn by the BKM 3.0’s fan to be fed to the device. At the inlet section, the VOC concentration is 50 ppm. At the outlet of the prototype a continuous stream of 30 cc/min is sampled through a peristaltic pump and analyzed in real time with a flame ionization detector (FID), calibrated on the specific VOC. For every test, the background signal value with both lamps turned off is measured (IUVC OFF), and then the signal with lamps turned on (IUVC ON), both acquired with the fan in operation at a constant flowrate. The percentage abatement of VOC is calculated by the percentage difference between IUVC ON and IUVC OFF. The ON-OFF cycles are repeated multiple times to ensure the reproducibility of the results.
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Figure 2. Outline of the setup used for the abatement of VOC on the BKM 3.0 prototype.
5. Results Results are expressed in terms of abatement of VOCs and pathogens in the air for a single passage inside the device. Each passage allows to treat the volume of air drawn by the device in less than a second.
Pathogens abatement The results regarding the removal of aero-dispersed pathogens by BKM 3.0, at the two different settings for the fan flowrate, are reported in Table 1. Table 1. Pathogens abatement at two fan speeds
Treated air flowrate [Nm3/h] 20 45
Single-passage PATHOGENS abatement [%] 99.5 96.4
VOC abatement The results regarding the VOC removal by BKM 3.0, at the two different settings for the fan flowrate, are reported in Table 2. Table 2. VOC abatement by BKM 3.0 at two fan speeds.
Treated air flowrate [Nm3/h] 20 45
Single-passage VOC abatement [%] 9.2 3.0
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Interpretation of the device’s performances The neutralization of pathogens is found to be very high, especially considering that the stated performances are not those obtain with a static irradiation test lasting several minutes, but those of the actual device in its operation, with very low residence time of air inside the device (< 1 second). It needs to be clarified that unlike pathogens, whose concentration in indoor environments can vary in a substantial way due to the presence of possible carriers, the release in the environment of organic compounds tends to be more gradual. The performance relatingVOC to abatement reported in Table 2 can therefore be sufficient todecompose these pollutants faster than they are produced by certain sources . As an example, we can consider the legislative limits to VOCs emissions by construction elements and furniture, which are common sources of VOCs for domestic environments. The legislation considered is the German one [2], since Italy does not yet have laws regulating the emission of organic compounds in non-industrial settings. According to these threshold values, measured in accordance to EN ISO 16000-9:2006 [3], a single device is able to degrade volatile components emitted by construction materials or furniture at the highest value allowed by the law in rooms up to 132 m3.
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