Volatile Organic Compound (VOC) Reduction from Face Mask Wastes via a Microwave Plasma Reactor

Received: July 5, 2022
Revised: October 9, 2022
Accepted: October 17, 2022

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Cite this article:

Sanito, R.C.,  Bernuy-Zumaeta, M., Yang, H.H., Wang, Y.F. (2022). Volatile Organic Compound (VOC) Reduction from Face Mask Wastes via a Microwave Plasma Reactor. Aerosol Air Qual. Res. 22, 220266. https://doi.org/10.4209/aaqr.220266

HIGHLIGHTS

• Pyrolysis of face mask generates volatile organic compound (VOC).
• Addition of Al₂O₃, CaCO₃, SiO₂, and cullet/glass decreases the total concentration of VOC.
• Vitrification of facemasks can be obtained via the addition of flux agents.
• Al–O–Al, Si–O–Si, and Si–O functional groups exist in the vitrification materials.

Keywords: CaCO3-SiO2-Al2O3-cullet, Face mask, VOC, Plasma technology, Vitrification

1 INTRODUCTION

Since the outbreak of COVID-19 pandemics, the driven of face mask as the personal protective equipment has increased significantly and should be concern as the medical waste. Also, face masks have been a concern as untreated medical waste since the COVID-19 spread, which has caused an effect on the environment (Zambrano-Monserrate et al., 2020; Ray et al., 2022). Akarsu et al. (2021) noted that face mask waste can be found around several locations, such as hospitals, bus stops and playgrounds, should be considered as the medical waste. Urban and Nakada (2021) reported that Brazil had generated face mask more than 35% of the medical waste. Torres and De-La-Tore (2021) confirmed that 74.9 tons day^–1 (27,344.7 tons year^–1) of face masks are generated in Peru. Nzediegwu and Chang (2020) noted that there are approximately 700 million face masks from a total of 15 countries in Africa. It is estimated that approximately 10 million masks waste are discarded in Italy from users every month (Singh et al., 2022). Zand and Heir (2020) confirmed that the highest amount of face mask waste was generated at a number of 10.78 million. In Taiwan, approximately 7 million mask wastes were generated since the outbreak of the COVID-19 (Sangkham, 2020). According to Ministry of Health and Welfare Taiwan (2020), over 50 million face masks have been donated to countries in Europe, Latin America, Asia-Pacific, Africa, Asia and Central America. Thus, the high number of facemask waste should be treated carefully.

Treatment of face mask wastes has become a serious issue since the outbreak of COVID-19. China has led the production of face masks and imported more than 2.0 billion face masks in 2020 (Wu et al., 2020). Indeed, the users of face masks should be high from across the globe. Thus, the amount of face mask wastes will increase significantly and cause the spread of COVID-19 if not handled properly (Mejjad et al., 2021). According to Kampf et al. (2020), corona virus may survive on the material surface for around 9 days. Tripathi et al. (2020) emphasized that SARS-CoV-2 virus persistence on the surface of the face masks is more than 7 days. Moreover, Kampf et al. (2020) stated that the millions of contaminated face mask are improperly managed. As a result, it causes environmental and health threats. Furthermore, the threat is high risk in several countries with the lack of waste management strategies and facilities, namely, a lack of landfills and non-appropriate recycling procedures. Therefore, open dumpsites and open landfills are options for handling the face masks (Sangkham, 2020; Torres and De-La-Tore, 2021). For instance, countries in Africa (Nzediegwu and Chang, 2020), Peru (Torres and De-La-Torre, 2021), Brazil, Chile, Mexico (Ardusso et al., 2021), India, Thailand, Indonesia, Philippines, Cambodia, Bangladesh, and Vietnam (World Bank, 2019; Ferronato and Torretta, 2019). Nonetheless, there are many concerns regarding how to handle the face mask wastes across the globe, and suitable further technology therefore should be considered owing to the high production of face masks for preventing the spread of SARS-CoV-2 viruses.

Plasma has been recognized recently as the fourth state of matter (Fridman, 2008) because of its ionization phenomena, which may deal with metals, metalloids, organic pollutants, VOCs, and microorganisms (Gomez et al., 2009; Sanito et al., 2020a, 2021, 2022a, 2022c, 2022d). Heberlein and Murphy (2008) stated that the advantages of plasma technology are associated with robust installation, fast heating, and cost savings. Moreover, the reactive species produced from the plasma system have a significant impact on the degradation pollutants (Locke and Shih, 2011). Thus, plasma technology can be considered as an alternative technology in dealing with the face mask wastes.

Some scholars have performed research associated with the use of plasma technology in dealing with polypropylene (PP) (Tang et al., 2003; Dave and Joshi, 2010; Maczka et al., 2013). Tang et al. (2003) stated that PP can be degraded via a nitrogen plasma reactor. Dave and Joshi (2010) also stated that plasma technology is a good solution for treating PP. As a result, syngas may be obtained from the process. However, volatile organic compound (VOC) from PP is a serious issue and harmful for the environment (Xiang et al., 2002; Yamashita et al., 2012; Kang et al., 2020). Some scholars also report that the composition of masks consists of polypropylene (PP), cotton, nylon, and filter paper (Ardusso et al., 2021; Torres and De-La-Torre, 2021; Mallick et al., 2021; Benson et al., 2021; Dharmaraj et al., 2021). Therefore, polypropylene (PP) from facemask wastes should be treated properly for preventing environmental pollution.

Flux agents have been widely used for vitrification and reduction of volatile organic compound (VOC) from the treatment of hazardous waste via plasma technology (Cubas et al., 2014, 2015; Du et al., 2018; Sanito et al., 2020a). Sanito et al. (2020a) discovered that adding flux agents, specifically CaCO₃ from shell powder in resin, reduced the total concentration of VOC by 82.34 ppm. Also, vitrification can be obtained from the waste with the addition of flux agents, for instance: SiO₂ and CaCO₃ (Cubas et al., 2015; Du et al., 2018; Sanito et al., 2020a, 2022b). As a result, VOC emissions can be reduced, and at the same time, vitrification of hazardous waste occurs, and elements can be encapsulated properly (Iwaszko et al., 2020). In this aspect, the addition of a flux agent can be considered in the treatment via plasma technology for reducing the concentration of VOC and vitrifying of face mask wastes. However, the information is still unclear.

This study investigated the effect of flux agent addition on the elimination of VOC facemask waste in the treatment via an atmospheric-pressure microwave plasma reactor. Moreover, the characterization of face masks before and after treatment is also evaluated. Based on author’s knowledge, the effect of flux agents to reduce the concentration of VOC from the face masks waste has not yet been fully studied. In this paper, it also said that waste face masks can be transformed into the glass using a microwave plasma reactor at the atmospheric-pressure.

2 MATERIALS AND METHODS

2.1 Collection and Preparation of Samples

One box of medical face masks (Chiu Fu Yu Co., Ltd.) was purchased from the medical shop in Taiwan (Represent face mask wastes in this study). The size of medical mask is 17.5 cm × 9.5 cm. The mask was cut using a scissor to obtain the smaller size (approximately 4 cm × 4 cm). After that, the smaller fragments of the masks were crushed using a pulverizing machine (Rong Tsong 0-2B, Taiwan). Furthermore, samples, which were obtained with the smaller fragment size, were put in containers. Approximately 2 grams of fraction from the mask was measured using the analytical balance (Shimadzu AUY-220, Japan). Fig. 1(a) shows the preparation of the facemasks prior to treatment in an atmospheric-pressure microwave plasma reactor.

Fig. 1. Preparation of face mask before treatment and atmospheric-pressure microwave plasma system. (a) Preparation of face mask wastes, plasma system and final residue, and (b) An atmospheric-pressure microwave plasma reactor system.

Meretrix meretrix shell samples were collected from the restaurant in Taiwan. The use of Meretrix meretrix as the source of CaCO₃ (flux agents). The samples were washed with deionized water (DI Water) for removing all the dirty parts of shells. In addition, all the shells were washed with soap for cleaning the particles. Furthermore, samples were dried in the oven with the temperature 100°C for evaporating the water for around 1–2 days. Afterwards, samples were crushed using a pulverizing machine for obtaining the smallest size of samples. To obtain a 0.074 mm shell powder, a 200 mesh sieve was used for obtaining the samples, CaCO₃ from shell powder, SiO₂, Al₂O₃, and glass/cullet were used as the flux agents for building the crystalline network from the final residue.

 
2.2 VOC Assessment from the Samples

VOC emission from face mask pyrolysis was analyzed via a gas chromatography (GC; Agilent 6890 N-USA). The gas from the plasma pyrolysis was captured in the 1 L gas bag collector (Tedlar). The oven temperature of GC was set up at 32°C and increased to 200°C in 3 min. The column size of the GC was 60 mm × 0.25 mm × 1.00 µm. The number of R² was 0.99, which indicates a suitable linear gas standard.

 
2.3 Pyrolysis of Mask

Samples were put in the plasma crucible from metal materials. For creating the vitrification of materials, the flux agents, namely, CaCO₃, SiO₂, Al₂O₃ and glass/cullet, were added to the samples. Flux agents contained 3 g of glass/cullet, 2 g of Al₂O₃, 2 g of CaCO₃, and 2 g SiO₂. The pyrolysis was compared with only the addition of glass/cullet (3 g) and the absence of flux agents (control). Table 1 explains the design details information of the flux agents. Mixing samples were put inside the crucible. As a comparison, the treatment of face mask waste with the absence of flux agent was performed. Fig. 1(b) shows an atmospheric-pressure microwave plasma reactor system for this experiment.

To create the plasma jet, nitrogen gas was used as the carrier gas due to the high efficiency results (Sanito et al., 2022d). Nitrogen gas was purchased with from the company in Taiwan with the size of tube at 40 L. The flow rate was controlled at 9 L min^–1. Furthermore, the duration and microwave power were set up at 5 min and 1000 watt, respectively. The pressure of the gas was maintained at 30 psi. The position of the crucible was maintained at approximately at 4–5 cm from the plasma ignition (Sanito et al., 2020a). A plasma discharge was generated from a copper wire.

 
2.4 Analysis of Sample Characterization

A scanning electron microscope (SEM-EDX; Hitachi, S-4800, Japan) was used for identifying the elemental composition elements before and after treatment. The elemental analyzer (Vario el Cube, Germany) was used for analyzing the mass fraction of carbon, nitrogen, and hydrogen of the mask before and after treatment. The characterization of crystalline structure was analyzed via the X-ray diffraction (XRD; Bruker D8 Advance Eco, Germany) before and after treatment. The samples were scanned at the X-rays for the 5 minutes, where the 2θ scanning ranging from 10°–80°. XRD’s voltage and electric current were set up at 40 kV and 25 mA, respectively. Then, the crystalline structures appear at 2θ.

The functional group in the sample was determined by Fourier transform infrared spectroscopy (FTIR: IRSpirit, Shimadzu, Japan). The ranges of wavenumber were 400–4000 cm⁻¹ (radiation of infrared). Samples are pelleted with the kBr. The sample was pressed with a manual hand press until it reached a thickness of 1 mm. A manual hand press was used to press the sample until a 1 mm thickness can be obtained. Samples were scanned in 2 min, via the infrared rays, generated by the FTIR system.

2.5 Analysis of Samples

Some elements from the mask fraction were analyzed via the ICP-AES (Shimadzu ICPE 9820, Japan). The flow rate of the argon gas was controlled at 10 L min^–1. The controls of auxiliary gas and carrier gas were set at 0.60 L min^–1 and 0.31 L min^–1, respectively. ICP AES power was controlled at 1.20 kW. Furthermore, the exposure time was controlled at 30 s. Samples were tested two times. The result of an ICP-AES gives the concentration from all the elements from solid phase to liquid phase (Sanito et al., 2020a).

 
2.6 Statistical Analysis Using ANOVA

To analyze the different effects of the flux agents on the VOC degradation, analysis of Variance (ANOVA) was performed. Minitab software version 16 was used to analyze the data obtained from the experimental data (Sanito et al., 2022b). The number of p-values represents the results the effect of parameters. Comparisons of pairwise of each parameter were analyzed via the Tukey, Fisher and Hsu multiple comparison with the best (MCB) (Khan, 2013).

 
3 RESULTS AND DISCUSSIONS

 
3.1 Effect of Flux Agents for Degrading Volatile Organic Compounds (VOCs) from the Face Mask Wastes

Table 2 shows the comparison results of VOC from face masks waste after treatment via an atmospheric-pressure microwave plasma reactor. From the study, the total VOC concentration with the absence of flux agents after treatment of face masks via an atmospheric-pressure microwave plasma reactor was 448.04 ppm. Moreover, the total concentration of VOC was 133.27 ppm with only the addition of cullet. The best results on the elimination of total VOC were obtained at the value of 54.7 ppm, where face mask wastes were combined with Al₂O₃, CaCO₃, SiO₂ and cullet, confirming lower than control and face masks with cullet at the values of 314.77 ppm and 393.34 ppm, respectively.

Fig. 2 shows the comparison results for the treatment of face masks waste with the absence and addition of flux agents. The highest concentration of pollutants in the pyrolysis of face masks was benzene. The concentration of benzene was obtained at a value of 237.73 ppm (53.05%) in control. Moreover, it was followed by toluene with a concentration 75.27 ppm (16.80%). Propylene can be found at the concentration of 56.63 ppm (12.64%) from the study. Lastly, other pollutants were found with a concentration of less than 36 ppm (less than 8%). Kerkeling et al. (2021) confirmed that the mask samples consist of xylenes, terpenes, aldehydes and siloxanes. Compared to the control, the addition of cullet and flux agents has better results. Final concentrations of benzene from face masks with cullet and face mask with flux agents (combination of CaCO₃-Al₂O₃-SiO₂-glass/cullet) were 58.48 ppm and 43.28 ppm, respectively, which are, respectively, 179.25 ppm (53.05%) and 194.45 ppm (43.88%) less than result of control (face mask only). Furthermore, the high percentage composition of benzene at 79.12% (43.28 ppm) in Fig. 2(c) dominates the composition of VOC due to the successful reduction of tetrahydrofuran, chlorobenzene, m-xylene, o-xylene, p-xylene, styrene, 4-ethyltoluene, benzene and toluene. Moreover, cullet and flux agents also showed a good result on degrading toluene with the value of 17.56 ppm (13.18%) and 5.54 ppm (10.13%), respectively, which are, respectively, lower than 57.71 ppm and 69.73 ppm, compared to control with a concentration of 75.27 ppm. The statistical model confirms that (F(4.34) = 0.04, p > 0.05), confirming the addition of flux agents has a significant impact on the reduction of the total VOC concentration (Table 3).

Fig. 2. Comparison results of VOCs on the treatment of face mask. (a) Mask (Control), (b) Mask combined with glass/cullet, and (c) Mask combined CaCO₃-SiO₂-Al₂O₃-glass/cullet.

Table 4 gives the results of the Tukey and Fisher analyses. The total concentrations of VOC and flux agent type levels significantly overlap based on the statistics. The grouping results of Tukey and Fisher confirm that the addition of flux agents had a significant effect to reduce the concentration of VOC, where the mean can be obtained at the value of 13.25 (Khan, 2013). The Hsu MCB confirms the best group from the analysis where it refers to the best result on the degradation of VOC with the addition of flux agents (CaCO₃, Al₂O₃, SiO₂ and glass/cullet). Also, it confirms that the high degradation of VOC with the addition of flux agent has the significant impact on degradation of VOCs from the face mask waste compared to control and glass (the best results). From this study, the lowest is the best because the decrease of total VOC concentration confirms the best result of plasma pyrolysis. The values of VOC in the gas emission and flux agents from the statistical evaluations are 0.00 and –20.22, respectively (Table 5). It shows that final concentration on the reduction of VOC with the addition of flux agents was better than in other groups, where the mixing of different flux agents (CaCO₃, Al₂O₃, SiO₂ and glass/cullet) plays a major role in degrading the total VOC concentration from the pyrolysis and has a significant impact during the degradation process.

Pollutants, namely, chloromethane, 1.3 butadiene, tetrahydrofuran, chlorobenzene, and 4-ethyltoluene were degraded perfectly at the value of 100%, with the addition of cullet and flux agents (CaCO₃, Al₂O₃, SiO₂, and glass/cullet) (Table 2). Furthermore, the addition of flux agents showed a significant difference compared to the absence of flux agents (p-value < α, where 0.04 < 0.05) based on the statistical analysis. It indicates that the addition of flux agents (Al₂O₃, CaCO₃, SiO₂ and cullet) has a significant impact on the destruction of VOC from the pyrolysis via an atmospheric-pressure microwave plasma reactor. The degradation patterns of pollutants of VOC with different flux agents are shown in Fig. 3(a) and Fig. 3(b). Overall, the results showed that the addition of flux agents indicates a better result compared to the control on the degradation of VOC. Pollutants, such as chloromethane, benzene, toluene, and 1,3-butadine, have concentrations of less than 100 ppm after the pyrolysis treatment with the addition of flux agents. Some pollutants indicate a trend lower than 4 ppm, such as chloromethane, tetrahydrofuran, chlorobenzene, ethylbenzene, m-xylene, o-xylene, p-xylene, styrene, and 4-ethyl toluene. Therefore, the degradation of pollutants can be obtained via the addition of flux agents during plasma pyrolysis.

Fig. 3. Degradation pattern of VOCs via an atmospheric-pressure microwave plasma reactor. (a) Concentration range from approximately 50 ppm–237 ppm and (b) Concentration less than 8 ppm.

Sanito et al. (2020a) confirmed that the addition of flux agents indicates an excellent result on degrading benzene and propylene from the treatment of resin via an atmospheric-pressure microwave plasma reactor. Sanito et al. (2022b) also stated that the flux agent addition from shell powder, especially from Babylonia formosae indicates a promising result on decreasing of the volatile organic compounds (VOC) from the plasma pyrolysis. In this study, the fuse of diverse flux agent gives a good result on degrading VOC from the face mask wastes, comparing with cullet and control because of the decrease of VOC. Thus, the addition of flux agents can be considered on the reduction of total VOC concentration. Degradation of VOC may be due to the presence of OH radicals (Wessenbeeck, 2016) in the flux agent, reacting with electrons from plasma jets and colliding with molecules of VOCs (Sanito et al., 2020a, 2022b). It is supported by the statements of some authors (Saunders et al., 2003; Bloss et al., 2005; Waring and Wells, 2015) that VOCs can be degraded owing to the presence of OH radicals. Degradation of VOC is therefore having a better result with the presence of flux agents compared with the absence of flux agents. The detail mechanism of VOC degradation is showed in Fig. 4.

Fig. 4. Mechanism of degradation of VOCs with the addition of flux agents.

 
3.2 Vitrification of Face Mask Wastes

Fig. 5 shows the result of vitrification after the treatment of face mask wastes via an atmospheric-pressure microwave plasma reactor. From this study, it can be seen in Fig. 5(a) that the pyrolysis of face mask waste has no vitrification results, comparing with the addition of flux agents with combinations, such as SiO₂, CaCO₃, Al₂O₃ and cullet. This is because of flux agent melted with materials, creating encapsulation and establish the silicate network. Based on the vitrification results, formation of crystalline structure can be obtained as follow: Silicon (PDF Number 1–791), Quartz (PDF number 1–649), calcium aluminium oxide/Ca(AlO₂)₂ (PDF number 1–888), Rankinite/ 3CaOSiO₂ (PDF number 2–323) and wollastonite/CaSiO₃ (PDF number 1–720) (Fig. 5(b)). It can be seen from Fig. 5 that there are many formations of crystalline structures can be established from the addition of flux agents compared to control, where some peaks appear from the analysis with the fuse of flux agents. ICP tests confirmed that the concentrations of Ca were more than the detection limit (Table 6). Also, the harmful elements are not detected from the ICP test, where the concentrations are 0 mg L^–1 with the fuse of flux agents. Cubas et al. (2015) confirmed that the addition of SiO₂ creates the silicate network from the face mask wastes. Du et al. (2018) and Sanito et al. (2020a) also confirmed that the fuse of flux agent improves the vitrification of materials from the hazardous waste. Interestingly, the presence CaSiO₃ because the using of Meretrix meretrix shell powder as the flux agents. Sanito et al. (2020a) found that the addition of shell powder (Babylonia formosae) creates the CaSiO₃ formation in the material from the plasma pyrolysis. Shell powder, therefore, has contributed to the vitrification of face mask wastes during the pyrolysis. The addition of CaCO₃, Al₂O₃, SiO₂ and cullet gives variation of material structures from the face masks.

Fig. 5. Characterization of face mask wastes after treatment with plasma technology. (a) XRD analysis of face masks wastes with the absence of flux agents. (b) Face mask wastes treatment with addition of SiO₂, Al₂O₃, CaCO₃ and glass/cullet.

Fig. 6 gives the result of FTIR characterization of the atmospheric-pressure microwave plasma reactor. The control results indicate the presence of CH₃ at a value of 995.7 cm⁻¹ and 995.7 cm⁻¹, respectively. Moreover, the wavenumber at 1647 cm⁻¹ related to the CH₂. The treatment of face mask wastes with absence of flux agent indicates the presence of CH₂ and CH₃ with values of 1530 cm⁻¹ and 1647 cm⁻¹ (Fig. 6(a)). In addition, the analysis of FTIR from the samples with addition of glass confirms the presence of SiO₂. Akarsu et al. (2021) stated that polypropylene had a percentage of up to 27% and polyethylene with the value of 51% from the masks. Thus, main compositions are polypropylene and polyethylene in the face mask wastes. In this study, the degradation of carbon affects the different composition or the functional groups in the face masks due to the transformation of materials during plasma pyrolysis. Szefer et al. (2021) indicated that polyethylene fiber is the main composition of the face mask wastes. Moreover, it consists of the microfibers (Saliu et al., 2021). Thus, the polypropylene is the main composition of face mask waste. Wavenumbers at value of 469 cm⁻¹ and 995.7 cm⁻¹ represent Si–O–Si functional groups (Fig. 6(b)). Face mask wastes with the fuse of flux agent combination (Al₂O₃, CaCO₃, SiO₂, and cullet) show the presence of functional groups related to Al–O–Al, Si–O–Si, Si–O, C–O, and OH with the wavenumbers of 459.22 cm⁻¹, 469 cm⁻¹, 833.16 cm⁻¹, 874.38 cm⁻¹, and 3435 cm⁻¹, respectively. (Fig. 6(c)). Reig et al. (2002) confirmed that the presence of Si can be obtained at the value of 709 cm⁻¹–831 cm⁻¹. Naayi et al. (2018) also confirmed that the presence of OH can be obtained at a value of 3550 cm⁻¹. In this aspect, vitrification occurs because of the addition of flux agents, which transforms the functional groups of face masks (control), such as carbon to the vitrify materials. Thus, vitrification can be obtained from this study with the presence of Al=O, Si–O–Si, and Si–O functional groups.

Fig. 6. FTIR characterization. (a) Face mask wastes only (control), (b) Face mask wastes treated with cullet, and (c) Face mask wastes combined with CaCO₃-SiO₂-Al₂O₃-glass/cullet.

 
3.3 Organic Compounds of Face Mask Wastes

In this study, the percentages of carbon from control, addition of glass/cullet and addition of flux agents were obtained at values of 91.86 ± 2.24%, 8.48 ± 2.08% and 17.92 ± 10.08%, respectively. Table 7 shows the elemental analysis of the face mask wastes. A total percentage of hydrogen was obtained at the value of 0.56 ± 0.056% (control). The percentage hydrogen from face mask wastes combined with cullet and face masks with CaCO₃-Al₂O₃-SiO₂-cullet/glass were obtained at the value of 0.85 ± 0.42% and 0.13 ± 0.01%, respectively. Moreover, the compositions of nitrogen from control, face mask wastes combined with cullet and face mask wastes combine with flux agents were 0.590 ± 0.056%, 0.03 ± 0.001%, and 0.13 ± 0.008%, respectively. The presences of C, H. and O from the face mask are associated with the polypropylene with the combining structure of C, H, and O. Also, the presence of polypropylene with a high density related to the inner and outer layers is always related to the presence of plastics (Fadare and Okoffo, 2020).

Information about SEM-EDX is outlined in Fig. 7. From this study, it can be seen that the surface formation of the mask after treatment via the plasma pyrolysis is more irregular and not spherical (Fig. 7(a)). The material from the plasma post-treatment with the addition of cullet indicates the conversion of materials with the spherical formation (Fig. 7(b)). Moreover, the compact structures can be obtained with the addition of flux agents with the combination of SiO₂, Al₂O₃, CaCO₃ and cullet, which successfully convert the face mask waste to different material formations, confirming the proper vitrification result of material from the plasma post-treatment, and it is linked to each other (Fig. 7(c)). From the plasma post-treatment, the Ca formation increases from 1.76% to 13.55% because of the addition of shell powder in the flux agent, where the percentage of C was 25.21%–47.16% (Table 8). In this case, the addition of more flux agents confirmed the high vitrification material of the residue. Sanito et al. (2020a, 2022b) confirmed that the addition of shell powder plays an integral role in the vitrification of hazardous waste. In this study, the addition of shell powder as the source of CaCO₃ from the Meretrix metertix shells combined with SiO₂, Al₂O₃, and cullet/glass may be suggested for the suitable vitrification of face mask wastes.

Fig. 7. SEM-EDX result of face masks from the post-treatment with the addition of flux agents (CaCO₃-SiO₂-Al₂O₃-glass/cullet).

 
3.4 Future Perspectives of the Face Mask Wastes Treatment

Near the future, the prevention of the pandemics will become a huge issue because related to the high usage of face masks during the pandemic era. In this aspect, the use of face masks will increase because for preventing the outbreak the virus to the environment, where will become a problem to the capacities of the systems for treating the face mask wastes (Ma et al., 2020). Technologies, such as incinerator (Kerkeling et al., 2021) and plasma (Gomez et al., 2009; Cai and Du, 2021; Zaluska et al., 2022) will be used to treat the medical waste. The proper type of flux agents should be suggested for dealing with the medical waste, considering the cost issues and vitrification results. Also, the environmental and economic evaluation should be performed to understand the cost issues to deal with the medical waste with the addition of flux agents and it may be potentially applied in the real system of plasma technology (Sanito et al., 2020b). Further idea related to the reuse of material from the plasma post-treatment for the construction applications may be suggested (Cubas et al., 2015).

 
4 CONCLUSION

In this study, the fuses of flux agents were reported to play an integral role for degrading the VOCs from the face mask wastes via an atmospheric-pressure microwave plasma reactor. Results confirmed that the addition of flux agents, with the combination of CaCO₃, Al₂O₃, SiO₂, and cullet/glass, successfully creates the vitrification of the face mask wastes and reduces the total concentration of VOCs via an atmospheric-pressure microwave plasma reactor. Pyrolysis of face mask wastes produced VOCs, namely benzene, 4-ethyltoluene, toluene, tetrahydrofuran, propylene, m-xylene, o-xylene, p-xylene, and styrene. The combination of CaCO₃, Al₂O₃, SiO₂, and cullet improves the removal efficiency of VOCs pollutants compared to control and cullet. Moreover, the addition of flux agents generates the vitrification of the final residue from the plasma post-treatment. The high composition Ca and Si with the value of 13.55% and 19.12% confirms the vitrification of face mask wastes, where the crystalline structure occurs. Also, the composition of carbon with the addition of flux agents was 17.92 ± 10.08%. Further research should be focused on conducting studies related to modification of an atmospheric-pressure microwave plasma reactor system. Furthermore, treatment of face mask wastes with the addition of flux agents in the real application should be performed to assess the possibility of the implementation for the pyrolysis treatment.