*2.1.3.5 Advantages and limitations*

Using UVC (200-280 nm) radiation has been successful in inactivating various viruses. This physical technique is non-toxic, non-corrosive to medical devices and environmentally friendly, it does not have to be portable. The disinfection time is reduced when complementary devices are used. However, this type of radiation is not highly penetrating and it may be ineffective of masks. Handling this type of radiation presents a significant danger for the human health. Primary skin cancers can manifested after a long period. So, the ICNIRP have reported the limit values for exposure to this kind of radiation [39].

#### **2.2 Gamma rays irradiation**

#### *2.2.1 Virus inactivation*

When Cobalt 59, the natural state of Cobalt, is bombarded with neutrons, it produces a synthetic radioactive isotope of Cobalt-60, which decays by beta disintegration to the stable Nickel-60. The gamma emission obeys the following Equation [40]:

$$\mathrm{^{59}\_{27}Co} + n \rightarrow \mathrm{^{60}\_{27}Co} \rightarrow \mathrm{^{60}\_{28}Ni} + e^- + \text{gamma-radiation} \tag{3}$$

The Gamma irradiation emitted by Cobalt 60 was performed sterilization in food science and to develop vaccine [41]. In fact, the treatment consists to irradiate products until 50 kGy and it known as bio-security of food. The required doses depend on the nature of microorganisms (bacteria, virus, pathogens and parasites).


**Table 2.**

*The required D90 (maximum and minimum) values of some virus and their properties [42].*

*Coronavirus Disinfection Physical Methods DOI: http://dx.doi.org/10.5772/intechopen.99091*

The required dose to inactivate 90% of microorganisms depends on environmental factors such as water content, media and temperature. The process of inactivation consists to induce damage in intercellular acids as a physicochemical damage in a single-strand break or double-strand break. Two processes can damage the DNA: **(1)** direct energy deposition;**(2**) secondary interactions with surrounding water molecules which permitting the formation of OH� free radicals. The irradiation susceptibility of virus is lower than other microorganisms; this is due to their low dimension. The estimated dose D90 (minimum and maximum) to inactivate various virus was reported in **Table 2**. The structure, size and the presence of envelop was also indicated.

#### *2.2.1.1 The target theory*

The inactivation of viruses by irradiation is perfectly described by the target theory. In fact, the hit probability P for N targets to be hit n times by radiation is described according the following equation:

$$P = \left[ 1 - e^{-\nu D} \sum\_{k=0}^{n-1} \frac{\left(\nu D\right)^k}{k!} \right]^N \tag{4}$$

Where *D* and, *ν* are respectively, the radiation dose and the target volume. The single-hit-single-target model corresponds to one targets, n = 1, and to be high one time by radiation, n = 1. So, the hit probability is reduced to Eq. **(5)**.

$$P = \mathbf{1} - e^{-\nu D} \tag{5}$$

The quantity, *νD* is connected to the fluence, *F*(particles/cm<sup>2</sup> ), and the inactivation cross section, *<sup>σ</sup> cm*<sup>2</sup> ð Þ, according the following Equation [41]:

$$
\nu D = F D \tag{6}
$$

#### *2.2.1.2 Corona virus inactivation by gamma irradiation*

In a recent work, Feldmann et al. [43], have studied the effect of gamma irradiation on infected tissues with Coronavirus. They have used doses ranged between 10 kGy and 40 kGy and found that the virus was completely inactivated at 10 kGy and recommend a 20 kGy dose. Several authors [44–46], have studied the disinfection of N-95 masks. These masks are designed to filter 95% of particles of size 0.3 μm. However, in this doses range (10 kGy-20 kGy), radiation can damage the masks tissues because of the cross linking and/or scissioning polymer [47]. It was shown also that the inactivation of Coronavirus depends on the infected medium, which can reduce the required D90 doses to 0.5 kGy [48].

#### *2.2.1.3 Advantages and limitations*

Gamma ray irradiation produce uniform dose and can travel through the surface due to their highly penetration depth. The technique does not induce an increasing of temperature; the disinfection time is about few minutes in maximum. However, gamma radiation requires an adequate and expansive device. This method can damage medical devices.

#### **3. Heat treatment**

#### **3.1 Heat treatment as major method for SARS-CoV-2inactivation**

Since the onset of the Covid-19 pandemic, the influence of temperature has been the subject of intensive discussion among epidemiologists about its influence on the dynamics of the spread of the virus on the one hand and its inactivation on the other hand. Such a debate seemed obvious given that heating has long been considered as the acquired effects of this thermodynamic parameter as well as on the physicochemical properties of biological macromolecules (proteins, enzymes, etc.) and microorganisms (viruses, parasites). From this point of view, the change in temperature could induce changes of conformational nature, the destruction (and formation) of chemical bonds, changes in physical phases which result in variations of a functional nature. Moreover, virologists have raised questions about the ability of high temperatures to destroy chemical bonds within the SARS-CoV-2 virus and to cause morphological variations in order to be able to inactivate its functions or reduce its virulence. Several works has been conducted in this regard to highlight how heating can help combat the Covid-19 pandemic. In this section we present the most uplifting among them [49–53].

#### **3.2 Heating to inactivate the virus**

From the first months of the pandemic, typical studies were carried out to observe the direct impact of an increase in temperature on the stability of SARS-CoV-2. They revealed that SARS-CoV-2 keeps its stability for 24 hours at a temperature of 37° C, On the other hand, heating up to 56° C for 30 minutes succeeded in inactivating the virus. However, such process preserved the stability of viral RNA in both human sera and sputum samples.

Te Faye and his collaborators [54] published a work in which they introduced a predictive thermodynamic model, based on the rate of a first order reaction and Arrhenius law. This model makes it possible to correlate data related to contamination and disinfection using heating. Their results provided very relevant information to help on the disinfection of protective equipment such as masks. For example, they have shown that exposing N95-type masks for 3 minutes can reduce the viral load of SARS-CoV-2 by almost 99%.

Batejat et al. [49] subjected cells infected with SARS-CoV-2 to 3 different temperatures and varying the heating time from 30 seconds to 60 minutes. They observed that SARS-CoV-2 could be inactivated in less than 30 minutes, 15 minutes and 3 minutes at 56° C, 65° C and 95° C respectively.

#### **3.3 Thermal inactivation improves RNA quality**

Based on what we quoted in the previous section on the heating power to inactivate the SARS-CoV-2, it seems evident that several laboratories would uses heating to reduce the risk of catching up with the virus.

Since virologists analyze the existence of viruses by conventional PCR and RT-PCR tests, a polymerase technique based on the extraction of virus RNA. So, to get the best results from PCR test, it is essential to have the virus RNA of better quality. In this context, questions were raised about the effect of heating on the quality of results obtained. Hemati et al. [50] exposed 36 samples from COVID - 19 patients to thermal inactivation (60° C for 30 min). The results were surprising and very

satisfactory. In fact, heating increased significantly the concentration of the extracted RNAs.

## **3.4 The use of microwave for hospital disinfection**

Another problem that raises concern in relation to combating the harmful effects of Covid 19 lies in the level of waste treatment, especially hospital waste of all kinds (medicine excretion, active component of drugs and metabolite, chemicals, residues of pharmaceuticals,,). It is also known that an important part of this waste is discharged into hospital wastewater, so the problem of disinfecting this water is an important challenge. For this, Wang et al. [51] have suggested several physical disinfection technologies of hospital wastes and wastewater to mitigate the virus spread in China. Among them, they used microwaves of frequencies between (2,450 50) MHz and (915 25) MHz in order to reach temperature of disinfection. Indeed, the heat of disinfection is generated by molecular vibrations in the medium traversed by the microwaves.

According to Ohtsu et al. [52], Microwave disinfection technology is an energy efficient technique, in which heat loss is relatively slow, fast acting. It is also characterized by its low environmental pollution since there will be no residues and toxic products left after disinfection.

## **3.5 Solar heating to inactivate the SARS-CoV-2**

Wang et al. [53] have proposed a simple, economic and ecological technique, which makes it possible to disinfect places with very high population density in which social distance is practically inapplicable, namely, cars, busses and other means of public transport (**Figure 1**).

The technique called "Solar heating for the deactivation of heat-sensitive pathogens", it is based on a simple direct exposure of cars to the sun heat for a few minutes during which the air temperature rises from 30°C to temperatures ranged between 50°C and 60°C. Wang and his coworkers [53] have assumed that this simple technique has already proven its effectiveness in in agronomy to kill weeds and soil pathogens. So, therefore it can be applied in the fight against covid-19 as a method of surfaces decontamination. The reported results of Wang et al. confirmed that hot air passively generated by Solar heating in enclosed spaces is an effective disinfection method with benefits without additional costs and chemicals. However, the disadvantage of this method is its dependence to hot climates. For this

**Figure 1.** *Schematic representation of car exposed to solar heat.*

reason, they assumed that the use of heaters in parking places could be a solution to overcome this handicap.

#### **3.6 Dry heat for masks disinfection**

Faced with the shortage of means of protection against covid-19 namely protective masks, Rubio-Romero published a paper review [55] in which he discussed the characteristics of the different types of disposable masks, considered as an alternative. To do this, he detailed the various methods of disinfection, in particular the physical methods of disinfection of deposited masks. Among these methods, he focused on dry heat disinfection. From this perspective, the main challenge was to guarantee total disinfection of the masks at temperatures over 56°C without affecting their filtering capacity. Based on this, both the Spanish Ministry of Labor and Social Economy and the International Medical Center of Beijing indicate that FFP respirators maintain their filtration efficiency after being disinfected at 70° C for 30 min.

#### **3.7 Use of cold plasma for SARS-CoV-2 inactivation**

Plasma is formed when a gas is subjected to a potential difference high enough to ionize molecules. As a result, the main properties of a plasma (electrical conductivity, etc.) depend essentially on the density of electrons but also on their volume fraction. The latter is directly influenced by temperature. Typically, the best known of plasmas is that of nuclear reactions, which is subjected to high temperatures of up to K. For this reason, plasma at ambient temperatures is called cold plasma or nonthermal plasma. At this temperature scale, cold plasma does find several industrial applications.

Cold plasma can be generated by applications of voltages ranging from 100 V up to a few kilovolts in direct current, and for radio frequencies in alternating current. In addition, this can only occur under very specific pressure conditions (a pressure between 1 Pa and 105 Pa).

#### *3.7.1 Cold plasma as a disinfection technology*

For years, cold plasma has been used to decontaminate and disinfect surfaces of steel, plastics, textiles ... It is also used to decontaminate some liquids and also air.

The disinfection technique is often known as «One Atmosphere Uniform Glow Discharge Plasma (OAUGDP)". The advantage of this technique is that it provides both uniform and low power density, which protects against any kind of damage to contaminated surfaces. This property gives it a strong implication in the medical field [56].

Several factors are involved in influencing the effectiveness of cold plasma disinfection. In this regard, mention may be made of the nature of the reactive species provided; it has been observed [57] that the use of oxygen species can support oxidation. The pressure conditions, the geometry of the electrodes ... It has also been observed that the speed of reactive species improves the inactivation of microbes. Increasing the applied electrical difference can play an important role in increasing the density of electrons, or even reactive species (**Figure 2**).

#### *3.7.2 Mode of inactivation of microorganisms by OAUGDP*

The mechanism of action of plasma on microorganisms is based on two simultaneous effects. The first effect is a thermal effect, which causes volatilization of cell

#### *Coronavirus Disinfection Physical Methods DOI: http://dx.doi.org/10.5772/intechopen.99091*

**Figure 2.** *The atmospheric pressure plasma jet (APPJ) as designed by Hermann et al. [57].*

membranes due to its exposure to plasma gas. This facilitates the exchange of proteins between the intracellular and extracellular media. The second effect is the result of the decomposition of organic and inorganic compounds by reactive species from plasma such as ozone, hydroxyl groups, nitric oxides ... [56].
