Coronavirus Disinfection Physical Methods

*Moez Guettari and Ahmed El Aferni*

#### **Abstract**

Since 2019, the spread of the Coronavirus pandemic becomes the global health crisis. To fight the pandemic, several measures were adopted such as: Hygiene measure, massive test, social distancing, quarantine and distancing. Disinfection is an important operation in the fight against the spread of Corona virus pandemic. The disinfection methods are of chemical and physical type. In this work, we focused our interest to the physical methods. These methods are classified in three principal categories: irradiation techniques, heat treatment and mechanical techniques. All the different aspect of techniques are exposed in this chapter. The efficiency of the used techniques is also discussed.

**Keywords:** Covid-19, disinfection, irradiation, heat treatment, mechanical treatment

#### **1. Introduction**

The COVID-19 pandemic is the global health crisis, with 133 991 203 infected persons and 2 903 728 deaths in the world until 09/04/2021 [1]. The virus responsible for the disease is mostly transmitted through aerosols. To fight the pandemic spread, several measures have been adopted such as the disinfection. This operation consists in reducing the number of microorganisms: viruses, bacteria, fungi … Eliminating all microorganisms is called sterilization [2]. Disinfection techniques are classified in two categories: Chemicals and physical types [3–6]. Applying a chemical agents such as acids, Alcohols, Aldehydes,Alkalis, Biguanides**,** Halogens, Oxidizing agents and Quaternary ammonium compounds, permits to disinfect surfaces and medical devices [4, 6]. Al-Sayah [6] has shown that the used chemical agents have excellent biocidal activity within a short time, easy to use and low toxicity. However, if chemical agents' concentration is high, the medical devices can be damaged and risk toxic effects on the technician [7]. Since 1908, Chick-and Watson have proposed a model to study the kinetics disinfection of water chlorination [8]. This model was refined by taking into account the disinfection process such as dissipating/volatile disinfectant [9–13]. The physical disinfection methods are classified in three categories: **(1)** Mechanical, **(2)** thermal treatment and **(3)** radiation effect [14]. The mechanical treatments include disinfection of surfaces by ultra-sound, plasma treatment and detergent action. Using ionizing or non-ionizing radiation (UV light, X rays, gamma rays, electron beam and heavy metals) is an important technique to disinfect surface. The efficiency of treatment depends on the penetration depth of the radiation; this is due to the wave length [15, 16]. The

thermal treatment consists of heating or cooling medical devices. In this context, cold plasma was considered as an emergent disinfection technology [16]. Heating infected medical devices by using steam under pressure or autoclave is a routine procedure in health care. In this chapter, we focus our interest on the disinfection physical methods used to fight Coronavirus spread. As we have mentioned previously, in a first step the different disinfection categories are discussed and so their efficiency and limitations are reported.

#### **2. Irradiation techniques**

The radiation includes non-ionizing radiation, such as UV rays, infrared rays,... etc. and ionizing radiation, such as α-β particles, neutrino, X-rays, �rays, the two last radiation are considered as indirectly ionizing radiations. The most common irradiation techniques used for killing Corona virus are UVC and -X rays.

#### **2.1 UVC irradiation**

#### *2.1.1 The germicide lamps*

UV light spectrum is ranged between 400 and 100 nanometers. It can be divided in three categories: UVA (400–315 nm), UVB (315–280 nm) and UVC (280– 100 nm). The UV radiations are emitted by the sun, but UVC does not reach the earth's surface due to the ozone layer in the atmosphere. The UVC is known as a powerful radiation to inactivate microbes and virus especially for the wavelength 254 nm. This type of radiation is produced artificially by the so called Germicidal lamps and microbes as it reported by several authors [3, 16–18]. The disinfection efficiency depends on lamp placement, mixing degree of room air, room configuration, lamp age air movement patterns and relative humidity, RH. Considering respectively, N0 and N, the number of initial micro-organisms at t = 0 s, and at a given time t. According to Kaniho and Ohgaki [17], N and N0 can be connected by the following Equation [17]:

$$N(t) = N\_0 e^{-Z\ln t} \tag{1}$$

Where, Z(cm<sup>2</sup> /μWs) and I(μW/cm2 ) are respectively the microorganism susceptibility factor and the UVC lamp intensity. Several authors [18, 19], have shown that the susceptibility parameters depends RH, where UVC effectiveness decreases with increasing relative humidity [19]. In practice, the dose received by microorganisms by surface unity is considered to estimate the efficiency of a lamp. In fact the dose, *D*, is calculated according Eq. **(2)**:

$$D = \text{It} \tag{2}$$

Where, I (μW/cm<sup>2</sup> ) and t(s), are respectively the UVC lamp intensity and the irradiation time. The required dose to inactivate 90% of microorganisms is denoted D90. We report in **Table 1**, required dose, D90, to inactivate bacteria in different conditions and medium (water, surface, air-low RH and air-high RH).

The SARS-CoV-2 inactivation dose corresponds to D90 = 7 J/m2 [21, 22], its susceptibility is 3 times greater than common cold virus (Influenza). Recently, Heilingloh et al. [23] have shown that the UVC required dose for complete inactivation of a high infected sample after 9 min of irradiation corresponds to 10,48 J/m<sup>2</sup> . The sample was at a distance 3 cm of the UVC source.

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


#### **Table 1.**

*The required D90 values of some bacteria in different conditions and medium [20].*

#### *2.1.2 The Corona-virus inactivation process*

UV-C (254 nm) is the most effective germicidal region of the UV spectrum. In fact, the UVC light is absorbed by DNA and RNA, causing photochemical damage and fusion of pyrimidines. The pyrimidine dimmers interrupt transcription and replication of RNA and DNA and so inactivate the virus [24]. The different devices using UVC technique revolve around the disinfection unit type, where complementary devices are used to ensure maximum efficiency. Certain devices can be mobile or ordered. The device types are discussed in the next sections.

## *2.1.3 UVC devices*

#### *2.1.3.1 Conventional lamps and UVC-LEDs*

The UVC radiation is generated by artificial sources, which we called disinfection unity. It includes lamps and UVC-Lamps. The lamps contain a gas, mercury or xenon, or a mixture of gases such as xenon-mercury (in small quantity), however UVC-LEDs are manufactured from semiconductors [25, 26]. The UVC-LEDs are an alternative to conventional lamps due to their compact size and energy saving. However, their cost is relatively high, light emitting (UVC-LEDs can be continuous or pulsed.Several authors have reported that pulsed UVC-LEDs are more effective then continuous and conventional lamps [27–29].

#### *2.1.3.2 Reflective wall and humidifiers*

To enhance the inactivation virus effectiveness, reflective wall and humidifiers are used as complementary devices. In fact, several authors [27–32], have shown that using reflective walls reduce the inactivation microorganism's time. On the other hand, Woo et al. [33], have shown that using deionized water as humidifier enhance the disinfection effectiveness.

#### *2.1.3.3 Chemical disinfectant*

Usually, disinfectant devices are combined with chemical disinfectants and were used to inactivate microorganisms in hospitals. Usual lamps and/or UVC-LEDs were used with gaseous ozone and hydrogen peroxide vapor. Several authors [34, 35], have shown that using chemical agents, such as hydrogen peroxide vapor, in addition to conventional UVC treatment permit more effective disinfection**.**

#### *2.1.3.4 Mobile and automated UVC devices*

Disinfecting robot is an emerging technology used to fight against the spread of Covid-19 in public transport, hospitals and any closed areas. However, it

requires a mastery of mechanics, electronics and programming. In fact, the mobile UVC device, Tru-D, has been shown to be more efficient than the static device and inactivate microorganisms within a period between three and four hours [36]. It was also shown that the used robot is quicker than chemical agents such as hydrogen peroxide. In this context, Bentancor and Vidal [37], have used a programmed device to communicate with the robot using Bluetooth devices and can be operated thanks to a mobile application. Recently, Guettari et al. [38] have shown that mobile robots are the most efficient device to inactivate microorganisms and developed an i-Robot UVC, this robot is essentially composed with two lamps on the top. Several sensors are integrated to measure physical parameters such as temperature and humidity to control the mobility of the robot to detect motion and to avoid obstacles. The disinfection time is monitored by Wi-Fi.
