ALEXIS KUO

Age 15 | Victora, BC

Canada Wide Science Fair Bronze Medalist

Edited by Karan Thakur

At the beginning of the pandemic, the effectiveness of non-medical cloth-based masks at filtering small particles was widely studied. The aim of this project is to enhance a mask’s filtration efficiency yet have it remain affordable, accessible, and sustainable by tackling the issue of the droplets themselves. Applying the concept of flocculation, in which small particles are drawn together to form a large clump that can be easily filtered, to airborne droplets, a filter was coated in potassium alum crystals. It was hypothesized that the coating would help turn small particles into larger droplets by forming a larger conglomerate, which can then be blocked by the filter. Initial results indicated that the potassium alum-coated filter effectively blocked more of the red-coloured water from passing through to the second layer compared to the non-coated filter. In conclusion, the use of the potassium alum chemical coating may improve the effectiveness of filters in a sustainable and affordable manner.

INTRODUCTION

The aim of this project is to create a mask that is affordable, accessible, and sustainable but most importantly one that can block a large percentage of airborne droplets. Cloth masks are widely available to the larger population, but unfortunately, are not extremely effective against airborne droplets, or in protecting both the wearer and those around them (Adelson, 2021). The N95 mask is considered the gold standard mask because of its effectiveness in blocking both large, medium, and small droplets utilizing a combination of electrostatic and mechanical filtration systems (Adelson, 2021). At the start of the pandemic, the major drawback of the N95 was its shortage, therefore not widely available to the general population (Adelson, 2021). Now that the supply of N95 masks in Canada has caught up with demand, the proper use of N95s is the most decisive factor in whether the N95 is offering its full protection (Foxcroft, 2021). In order to reach full filtration efficiency, the N95 has to be properly fit-tested to decrease air leakage (Foxcroft, 2021). Conversely, non-medical masks are accessible and affordable, but solely rely on mechanical filtration and do not offer effective protection against smaller droplets (Adelson, 2021). Multiple layers can be used to enhance mechanical filtration and improve the efficiency of non-medical masks. However, an increase in the number of layers will increase airflow resistance, decrease sustainability, and cause respiratory discomfort, which can result in a reluctance against mask-wearing and discourage following mask protocols. Supplementary approaches are needed to improve the efficiency of filtration of masks against airborne droplets. Instead of inventing a new mask, or adding additional layers, this project looks at tackling the problem of the droplets themselves, sustainably and affordably. One such filtration technique, known as flocculation, utilizes a chemical process to change droplet size by aggregating suspended particles to form a larger agglomeration that can be easily filtered (Teh, 2016). Potassium aluminum sulphate is a common flocculate used during this process.

HYPOTHESIS

Applying this simple concept of flocculation that is used currently in the treatment of sewage water to airborne droplets, I hypothesized that the potassium alum would help convert small particles into larger ones by forming a larger conglomerate, which can then be blocked by the filter.

materials & methods

A supersaturated solution of potassium aluminum sulphate was prepared with a ratio of 30 g potassium aluminum sulphate in 100 ml of water at 20℃. Half of a PM2.5 filter, while the other half was suspended in the air to provide a control, was placed in the supersaturated solution for two hours to coat the filter, and then removed to be air-dried. The filter was sprayed with red-coloured water from 30 cm away. The water was dyed red to allow for easier observation, since clear water is hard to detect on the white filter surface. There were two phases to analyzing and assessing the coating. After spraying, each of the five layers of the filters was visually examined and a qualitative note of the intensity of the stained red colour on all the layers of the filter was recorded. To verify the results from the qualitative analysis, a quantitative analysis on the pixel intensity of the stained colour was performed with ImageJ, an image analysis software created by the National Institute of Health, on the second layer of the filter. The red-coloured water would have to pass through the first layer, for both the coated and non-coated sides, to land on the second layer. If more red-coloured water shows up on the second layer, the less effective the first layer was, since it allowed for more of the red to penetrate through. Using this concept, the second layer of the filter was chosen to provide an indirect measurement of the coating’s effectiveness compared to a non-coated first layer.

Five random sections per second layer of the filter per coated (C) and non-coated (N) side were selected and analyzed using ImageJ for a total of 50 sections, 10 sections for five filters. The ImageJ allows for calculation of the stained area versus the total area analyzed to provide a percentage value (National Institute of Health).

RESULTS

All five layers of the PM2.5 filter were qualitatively analyzed. First layer C was darker compared to its second layer. First layer N was also darker compared to its second layer. The third carbon layer decreased the visibility of the red colour. The red colour was not detected on the fourth and fifth layer for both C and N. Comparing the C and N sides of the first layer, C was darker than N. In contrast, the second layer N was darker than the second layer C (Fig.1). The quantitative results, using ImageJ, were obtained from the second layer of the filters for both C and N. After all 50 sections were examined, the average detected stained area of the second layer showed a similar trend, where C was lighter than N, with a detected stained area percentage and standard deviation of 2.38±0.26 intensity in C and 13.51±1.82 in N (Fig.2). Overall, the potassium alum-coated filter blocked more of the red colour from passing through to the second layer compared to the filter without potassium alum.

**Figure 2**: Quantitative results from ImageJ Analysis of Second Layer C and N filter. Bar graph showing quantitative data following ImageJ analysis of detected stained area from the second layer of the coated (C) and non-coated (N) filters. Calculated standard deviations were 2.38±0.26 intensity in C and 13.51±1.82 in N. Compared to N, the detected stained area in C is significantly decreased.

DISCUSSION

The current gold standard for masks is the N95. Cloth masks are widely available but not as effective at filtering droplets as the N95. The average N95 mask can capture 95% of particles which are roughly 0.1 to 0.3 microns in diameter, following standardized testing with NaCl particles (Qian et al., 1998). Surprisingly, the droplet size of greatest concern is the “medium” sized droplets, those between 0.1 to 0.5 microns, as these droplets are easily swept along with the air flow and current (Fleisher et al., 2020). Most masks, such as cloth masks, have the ability to filter small (< 0.5 microns) and large droplets (> 0.5 microns) but are not as effective against medium-sized droplet particles. The design and testing of N95 masks are tailored towards filtration efficiency against medium particles (Qian et al., 1998; Fleisher et al., 2020). The droplets created by spraying red-coloured water should fall within the category of medium airborne droplets, that are usually in the range of 0.5 microns or less (Fleisher et al., 2020). Therefore, the results from this project suggest that the potassium aluminum-coating was able to increase the PM2.5 filter’s filtration efficiency of medium droplets. In addition, the outer layers of the PM2.5 can filter up to 6-10% of particles, when tested using a modified N95 respirator testing procedure (Zhao et al., 2020). Theoretically, the potassium-alum layer should have a filtration efficiency greater than 6-10% as it performed better than the non-coated filter.

Potassium alum is an easily accessible and commonly used chemical flocculant in sewage treatment approved by the FDA for use, with skin irritations as long-term health effects (Pro Chemical & Dye, 2013). The size of the alum crystals formed on the PM2.5 filter measured between 0.2-0.6 mm (200-600 microns). There are currently no studies regarding the safety or health effects of inhaling potassium alum. There are studies that demonstrate breathing large amounts of aluminum can result in lung irritations (Agency for Toxic Substances and Disease Registry, 2015). However, the multiple layers separating the alum crystals from the wearer should be able to mitigate these effects by capturing these particles before they enter the respiratory tract. Furthermore, the potassium-alum crystals should not have a large effect, as the crystals on the coating are large, 200-600 microns in size, compared to the airborne droplets in this experiment, which are merely 0.1 to 0.3 microns in diameter. Additionally, the placement of the coating is not in direct contact to the wearer as it is the outer layer of the filter that will be coated. With the end of the pandemic in sight, the concept of adding a chemical coating to filters should not be limited to only mask filters but can be applied to all areas that utilize filtration systems to enhance their ability to function, such as HEPA filters, standard home air purification, home air conditioning, or water filtration.

CONCLUSION

Through both quantitative and qualitative observations, the potassium alum-coated filter was shown to have effectively blocked more of the red colour from passing through to the second layer compared to the non-coated filter. In conclusion, the use of potassium alum may improve the effectiveness of filters in a sustainable, accessible, and affordable manner.

ACKNOWLEDGEMENTS

This project would not have been possible without the help of my science teachers, Anne-Marie Simard and Erin Dallin, and my family, who provided me with support, energy, and time.

REFERENCES

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Zhao, M., Liao, L., Xiao, W., Yu, X., Wang, H., Wang, Q., Lin, Y. L., Kilinc-Balci, F. S., Price, A., Chu, L., Chu, M. C., Chu, S., & Cui, Y. (2020, July 8). Household materials selection for Homemade Cloth face coverings and THEIR FILTRATION efficiency enhancement with Triboelectric Charging. Nano letters. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7294826/#:~:text=Common%20fabrics%20 of%20cotton%2C%20polyester,efficiency%20of%2010%E2%80%9320%25.

Exploring an Affordable and Sustainable Approach to Enhance the Effectivness of Filters