## 4 Findings and Discussion
### Management of Waste
In another study, single-use FFP2 masks were sterilized by a 15 min procedure at 121 \({}^{\circ}\mathrm{C}\) using a dry sterilization process, which could be adjusted in standard autoclaves in hospitals, showing the effectiveness of these processes to inactivate the Coronavirus without influencing the functionality of the tested masks [25]. Liquids such as alcohol solutions, chlorine-based solutions, or soaps should not be used to clean the respirator, as this will lead to a degradation in the static charge that is necessary for the filtering facepiece respirator (FFR) to meet the N95 standard [28], whereas the application of spray-on alcohol-based solutions containing disinfectants on the top surface of masks does not result in a measurable loss of mask filter performance [57]. In addition, efforts to develop green and degradable materials for PPE should be applied to reduce the environmental impact of PPE waste, for example a novel self-sanitizing mask prototype that reduces unnecessary waste has been developed [58];
* Recycling should be the best solution for face mask waste. However, this is not easily achieved because of the difficulty in properly separating materials [59] and the their bio-hazardous potential [21]. Nevertheless, some studies have opened opportunities in this field. For example, biochar production through the co-carbonization of disposable face masks and waste biomass has been investigated, indicating the possibility of using the biochar as an adsorbent and to increase soil fertility [60]. Some alternatives explored the use of PPE waste to produce concrete for construction [61; 62] or the recovery of plastic particles from decomposed PPE [20];
* Finally, thermo-chemical processing offers a reliable treatment route for PPE to valorize face masks and other PPE using waste-to-energy technologies [30], including combustion [31; 63], gasification [64], and pyrolysis [32]. The incineration of single-use face mask waste could generate an estimated 32.65 and 6.03 million kWh/day of electricity in Asia and Africa, respectively, although the potential risk of acidification makes necessary the provision of air pollution control devices in incineration plants [65]. The plasma gasification technology produces both synthesis gas, which can be utilized to run compression ignition engines, but also byproducts, which can be further utilized as valuable inputs in other industries, strengthening the circular economy concept; for example, vitrified slag can be used for building aggregates, tiles, or bricks [64]. The gasification and pyrolysis processes can be applied to recover Zn and Fe from nonrecyclable steel-making byproduct dusts and waste plastic material, such as face masks [66]. The refuse-derived fuel (RDF) pyrolysis process from protective masks produces a high calorific value for pyrolysis gas, amounting to approximately 47.7 MJ/m3. This process has been also applied to the polypropylene (PP) powder derived from COVID-19 isolation gown waste to yield char briquettes [32]. In any case, all these processes encourage PPE waste management towards energy recovery. All these solutions are necessarily related to both the increase in public awareness for the sake of the collection and segregation of PPE waste at its source, but also the application of ecodesign practices in face mask production, such as the Extended Producer Responsibility (EPR) defined in Directive 98/2008 [67]. The EPR is an environmental protection strategy aimed at decreasing the total environmental impact of a product and its packaging by ensuring that the product's producers take responsibility for its entire lifecycle, especially through the take-back, recycling, and final disposal of their products [68]. It is included in Article 8 of Directive 98/2008, which directs Member States to take measures to ensure that any natural or legal person who professionally develops, manufactures, processes, treats, sells, or imports products has extended producer responsibility [67].