Mega-scale desalination efficacy (Reverse Osmosis, Electrodialysis, Membrane Distillation, MED, MSF) during COVID-19: Evidence from salinity, pretreatment methods, temperature of operation

Abstract

The unprecedented situation of the COVID-19 pandemic heavily polluted water bodies whereas the presence of SARS-CoV-2, even in treated wastewater in every corner of the world is reported. The main aim of the present study is to show the effectiveness and feasibility of some well-known desalination technologies which are reverse osmosis (RO), Electrodialysis (ED), Membrane Distillation (MD), multi effect distillation (MED), and multi stage flashing (MSF) during the COVID-19 pandemic. Systems’ effectiveness against the novel coronavirus based on three parameters of nasopharynx/nasal saline-irrigation, temperature of operation and pretreatment methods are evaluated. First, based on previous clinical studies, it showed that using saline solution (hypertonic saline >0.9% concentration) for gargling/irrigating of nasal/nasopharynx/throat results in reducing and replication of the viral in patients, subsequently the feed water of desalination plants which has concentration higher than 3.5% (35000ppm) is preventive against the SARS-CoV-2 virus. Second, the temperature operation of thermally-driven desalination; MSF and MED (70-120°C) and MD (55–85°C) is high enough to inhibit the contamination of plant structure and viral survival in feed water. The third factor is utilizing various pretreatment process such as chlorination, filtration, thermal/precipitation softening, ultrafiltration (mostly for RO, but also for MD, MED and MSF), which are powerful treatment methods against biologically-contaminated feed water particularly the SARS-CoV-2. Eventually, it can be concluded that large-scale desalination plants during COVID-19 and similar situation are completely reliable for providing safe drinking water.

Graphical abstract

1. Introduction

In the light of emerging the novel coronavirus form the beginning of 2020, the public health (at the forefront of this battle) was not the only sector which adversely affected but other sectors are severely get under pressure. Apparently, the huge environmental barriers as the results of the pandemic are one of these side effects which elucidated from different aspects from air/water/soil pollution to plastic wastes (Rume and Islam, 2020; Saadat et al., 2020). However, direct and indirect effects of contaminating water bodies via SARS-CoV-2 is more concerning and more dangerous since it directly related to the human health from different aspects, because the viral RNA is release to the environment through wastewater and it can be remain viable from days to weeks. Importantly, presence of the SARS-CoV-2 in water bodies would be threatening for millions of people who rely on water treatment and desalination systems to provide their drinkable water needs. In the context of providing safe drinking water with small-scale desalination systems such as solar distillations from biologically contaminated water a limited number of efforts have been made to realize the effectiveness of them (particularly small-scale systems) against pathogens (Malaeb et al., 2017). Ayoub et al. (Ayoub et al., 2015) examine the possibility of cross contaminating two pathogens of Escherichia coli and Enterococcus faecalis in desalination units to distilled water for different temperature ranges of 40-45°C and 50-55°C. The results of indoor experiments revealed that both pathogens are transmitted via vapor from desalination unit to the distilled water. Similarly, transfer of three other pathogens of Klebsiella pneumonia, Escherichia coli and Enterococcus faecalis in analogous solar desalination units in the absence of solar UV were examined to understand the mechanism of pathogens transfer through three parameters of water temperature (30-50°C), pathogens’ particle size, and type of sample water (Ayoub et al., 2014). The findings revealed that all pathogens are capable to transmit via vapor of desalination units while the highest rate of transfer occurred at 40°C. Furthermore, it was showed that particle size has direct effect on the pathogens transmission in which Enterococcus faecalis (particle size < 1µm) has the highest concentration in distilled water. However, the aforementioned studies focused on the bacteria rather viruses. Recently, Parsa (2021), presented a theory on the possibility of novel coronavirus (SARS-CoV-2) transmission via vapor of solar desalination units and concluded that under the most of conditions in various types of solar desalination configurations the novel coronavirus would be transfer via vapor to the collected droplets. As our main focus in this review is the novel coronavirus in desalination plant rather than other pathogens (because of the SARS-CoV-2 virus is greatly impacted various sectors of environment) one crucial question that should be answered is arise here; Is it possible to be infected by the novel coronavirus if it exist in the drinking water? In another word: Does presence of the SARS-CoV-2 in consumable water of people dangerous and threatening? To answer this vital question we need to know that the main transmission route of any disease is not the only way to result in infection but other routes are completely plausible. Numerous instances for transmission via off-centered routes are reported. Transmission via an off-centered route for a number of pathogens such as Ebola virus (Petrosillo et al., 2015; Vetter et al., 2016; Lalle et al., 2019), Vibrio Cholera (Kjær et al., 2020), Influenza A (Hinshaw et al., 1979) to name a few is reported. Interestingly, the risk of infection by contaminated water during the ongoing pandemic is also suggested in numerous studies. In a broader prospect, the first detection of SARS-CoV-2 in gastrointestinal tract rise many concerns about another route of spreading the virus called fecal-oral transmission (Xiao et al., 2020) whereas using numerical methods such as QMRA elucidated and further boosted the potential transmission of the virus via water media to human (Tyagi et al., 2022). Importantly, Bilal et al. (2020) brought the potential of water matrices as the source of SARS-CoV-2 transmission into the spotlight and concluded that various water matrices including groundwater and drinking water resources should be safe (particularly from SARS-CoV-2) enough in order to prevent another route of the virus spreading to human. Shutler et al. in a preprint (Shutler et al., 2020) put one step forward and proposed that there is no substantial difference in virus temporal survival and infection risk between freshwater and seawater whereas gathering data from 39 countries showed that considering SARS-CoV-2 as the waterborne disease to the human via rivers is serious concern (Shutler et al., 2021). Jiao et al. (2021) in a non-human model proved that the gastrointestinal tract can be considered as a transmission route of the SARS-CoV-2. Surprisingly, in a recent study published in Nature Communication, Giobbe et al. (2021) showed that SARS-CoV-2 virus can efficiently replicated in stomach of persons and leading to infections. Conclusively, due to the infection of gastric epithelium they concluded that the virus play an important role in fecal-oral transmission. Although many studies highlighted the effectiveness of various pretreatment methods such as ozonation, UV, chlorination, electrochemical process (Zahmatkesh et al., 2022; Zahmatkesh and Sillanpää, 2022), mix matrix membrane (Zahmatkesh et al., 2023) and biological treatment such as algae-based methods in wastewater treatment plants (Zahmatkesh and Pirouzi, 2020), the number of researches in the context of large-scale desalination plants during the ongoing pandemic is rare and those limited studies that could be related to the desalination technologies is focused on the role of some of the pretreatment methods against SASR-CoV-2. Nevertheless, some researches have been performed in the context of thermal desalination technologies by focusing on the use of nanomaterial as antibacterial agents for biological contamination, but they limited to the small-scale desalination (Parsa et al., 2020) system and the feasibility for large-scale plants has not been realized.

Thus, the main aim of this review is to realize the effectiveness of different desalination technologies for providing safe drinking water during the COVID-19 pandemic. To do this we are about to evaluate reliability of large-scale desalination technologies via three parameters which are effect of feed water salinity, temperature of operation, and various pretreatment methods that used in desalination technologies. Regarding the interdisciplinary approach of the review and to realize the main goal of study, the paper organized in several sections to follow a rational path in order to easily comprehend by readers in the field.

1.1. The road map of present study

As it mentioned above the present study separated in several section due to the multidisciplinary nature of the topic. Since the main route of entering biological contamination to water resources is wastewater, in the first section, contamination of water bodies via wastewater is briefly discussed. Afterwards, this section followed by presence and survival of the different viruses as well as SARS-CoV-2 in seawater because large-scale desalination technologies mainly used huge water bodies like seawater. In the next section mechanism and characteristics of NACL solution as an antiviral agent is discussed and it followed by more discussion on effectiveness of nasopharynx saline irrigation against the novel coronavirus. The aim of this section is to elucidate the sensitivity of the novel coronavirus to salinity (in different concentration) because the feed water of desalination plants is saline. In the next step principle of desalination plants briefly explained. It should be mentioned that an in-depth and detailed technical discussion about desalination plants was not performed in this section because the aim is to highlight the important principle of systems such as temperature of operation. In the next section various types of pretreatment methods associated with desalination plants are presented. Finally, in the last section, reliability of mega-scale desalination plants in providing safe drinking water regarding three aforementioned parameters which are temperature of operation, salinity of feed water, and pretreatment methods thoroughly discussed.

2. Contamination of water bodies

Human activities have a drastic effect on the aquatic environment whether on water bodies or biodiversity of a certain type of aquatic animals (Su et al., 2021). Although one third of the world's population lived in vicinity of rivers/banks/ floodplains, variety of environmental contaminations through the anthropogenic activities forced to these regions. Water bodies contaminated via different sources but the two most important factors that paly the key roles are the nutrients and pathogens produced (i.e. various bacteria, viruses, etc.) by human wastes. The origination of these pollutions are varied but wastewater is known as one of the major reasons that lead to these two source of contaminations (Best, 2019). The critical role of wastewater in contamination of water bodies stepped more into the spotlight when we consider that some of the huge transcontinental rivers and basins in the world such as Ganges, Amazon, Congo, Parana, Nile, Yenisey, Lena, Zambezi, Niger, Amur, Indus, Mekong, and Salween are polluted by various pathogens of wastewater (UNEP-DHI, 2016). Fig. 1 a, b shows various routes of contaminating water bodies during the pandemic.

Fig. 1.

(a) The likelihood of COVID-19 contaminating the urban and rural water cycle with potential human exposure (Bhowmick et al., 2020). (b). Transmission routes of SARS-CoV-2 virus to natural water bodies. WWTP = Wastewater treatment plant (Yusoff et al., 2021). Figures reprinted from open sources.

2.1. Seawater contamination by various wastewater sources

Oceans and seawaters are subjected to contaminate by sewages and urban/industrial/hospital wastewaters in recent years. These contaminations are more prevalent in developing countries where there are not effective sanitation networks. However, the problem of contamination by wastewater in some of the industrialized countries with developed economy is reported too (Parsa et al., 2021). Numerous examples of contaminating seawater and ocean throughout the world were reported. Contamination of Venezuela's center coastal in the Caribbean region by two different protozoa is scrutinized (Betancourt et al., 2014). Improper residential waste management, discharging sewage, wastewater, and ineffective sewer system are introduced as the main reasons of pollution. Furthermore, contamination of Tunisia coastlines in the Mediterranean Sea by industrial and domestic wastewater is observed (Houda et al., 2011). Also, it was reported that pharmaceutical/hospital and urban wastewater is the source of pollution in the Mahdia coastline in the Mediterranean Sea region (Afsa et al., 2020). Over 500 sewage-derived contaminations in the Atlantic Ocean due to urban wastewater were reported by Pablo and co-workers. They declared that these contaminations are identified at 50 Km far away from the shoreline and in the depth deeper than 500 m. This surprising findings revealed the fact that contaminations of water bodies not only adversely impacted the costal lines but in a massive water body such as the Atlantic Ocean various type of contaminations are detected at such distances and depths too (Lara-Martín et al., 2020). The other pollution path of oceans and seawater is through indirect via contaminated surface water and groundwater by wastewater and sewage. It is interesting to be noted that contamination of natural water bodies (that many of them can connected with the huge water resources such as seawater and oceans) (Kumar et al., 2021; Buonerba et al., 2021), rivers (Shutler et al., 2021), groundwater (Huo et al., 2021), and freshwater environment (Mahlknecht et al., 2021) via the SARS-CoV-2 are disclosed.

2.2. Presence of viruses in seawater

Coastlines and seawater always subjected to enter various types of microorganisms and pathogens such as bacteria, fungi, and viruses (Santhiya et al., 2011). Presence of different types of viruses in aquatic environment has been extensively explained in plenty of studies. However, a brief discussion about various types of these pathogens in seawater is presented. The most well-known viruses that have high potential for waterborne outbreak in human are Rotavirus, Calicivirus, Astrovirus, and some enteric adenoviruses (Leclerc et al., 2002). Leveque et al. warned about transmitting of enteroviruses to human by swimming in contaminated seawater (Leveque and Laurent, 2008) while Aller expressed the upper layer of sea (micro-layer) as the source of viruses and bacteria that enrich marine aerosols (Aller et al., 2005). Rebollo et al. examined the persistence of Lymphocystivirus in different types of seawater for temperature range of 18–22°C. Findings showed that the virus can remain viable between 2 and 242 days depending on the type of water media and temperature (Leiva-Rebollo et al., 2020). Dancer et al. also reported human Norovirus under simulated cold season conditions (temperature at 8°C and available UV 1 mW/cm²) can tolerated up to 140 h (Dancer et al., 2010) whereas (Tsai et al., 1995) declared that Poliovirus in seawater at both low and room temperatures (i.e., 4 and 23°C) is detected after three weeks. Contaminated samples of seawater of various viruses including Hepatitis A, poliovirus and somatic Salmonella bacteriophages from different coastal sites in California, Hawaii, and North Carolina were collected by Callahan and co-workers. Their findings revealed that 4log₁₀ reduction of Hepatitis A, poliovirus and somatic salmonella bacteriophages was achieved by around 4, 1, and 10 weeks, respectively (Callahan et al., 1995). Furthermore, it was disclosed that Hepatitis A viruses in synthetic seawater at temperature of 4, 19, and 25°C remains stable by around 92, 24, and 11 days, respectively (Crance et al., 1998). Dale et al. reported haemorrhagic septicaemia virus (HSV) outbreak in seawater that results in death of rainbow trout species in Norwegian sea (Dale et al., 2009) while Weli et al. examined the presence of salmonid Alphavirus in Norwegian sea in Oslofjord (Weli et al., 2021). Also Griffin et al. (2000) realized that more 90% of canals and near waters from 19 locations that poured to the Florida Keys have been positive tests for at least one group of enteroviruses. Interestingly, Wetz et al. evaluated the persistence of Poliovirus in different types of seawater at Florida Keys and found that temperature, concentration of pathogen/salt, and type of seawater play significant role in inactivation the pathogen (Wetz et al., 2004). Furthermore, in the context of COVID19, the SARS-CoV-2 can easily enter to oceans/seawater and contaminated the aquatic environment. This is not only an unlike statement but is a fact when we consider in a country like India with a dense population, nearly 60% of sewage without any treatment is directly discharged into environment (Bhowmick et al., 2020). This can increase the risk of pneumonia of aquatic mammalians (Nabi and Khan, 2020) and it would be more disturbing when consider this fact that cetaceans herds are migrated to long distances regardless of political/geographical boundaries (Van Bressem et al., 2014). Hence. it can be another route for transmitting pathogens to other sites via these secondary hosts.

3. Nasal and nasopharynx irrigation by antiviral solutions against SARS-CoV-2

Since the viral load of novel coronavirus in nasal and nasopharynx is high, nasal and nasopharynx irrigation by various antiviral agents proposed as a proper solution to reduce (if not eliminate) the viral load in these areas and diminish its viability. Researchers proposed different liquid-based solutions for irrigating/gargling such as Copper (Ramezanpour et al., 2020), Povidone Iodine (Etievant et al., 2020; Frank et al., 2020), hydrogen peroxide, Corticosteroids, Chlorpheniramine, Listerine, Chlorhexidine, and NaCl (Stathis et al., 2021; Go et al., 2021). However, there are controversial arguments about the use of these compounds against the SARS-CoV-2 because of different reasons. For instance, in the case of copper not only the toxicity of element is of great concern but releasing ROS (i.e., reactive oxygen species) or free radicals which damage cell structure is also highly preventive factor (Ameh and Sayes, 2019). Furthermore, the long-term use of povidone iodine results in damage to ciliary function due to the risk of dilution error, because povidone iodine is not always available as ready-to-use compounds in all regions (Nasal Saline Irrigations in the COVID-19 Pandemic—Reply 2021). Interestingly, the side-effects of hydrogen peroxide (which is well-known for its virucidal/bactericidal effect) irrigation of the nasal and nasopharynx is still unknown in the case of COVID-19 because of the lack of trial evidence on its safety (Higgins et al., 2020). Among three types of the saline gargling and irrigation which are liquid direction, powder direction, and the traditional method; the liquid-based is the most effective method among other methods. However, the effective use of saline solution for nasal irrigation and the health of respiratory system is proven before (Santoro et al., 2021). Fig. 2 illustrates the anatomy of nasopharynx, oropharynx, and hypopharynx of human.

Fig. 2.

Anatomy of nasopharynx and oropharynx.

3.1. Effectiveness of NaCl as an antiviral agent and mechanism for pulmonary phagocytic/non-phagocytic cells

Until now, the direct effect of NaCl on the SARS-CoV-2 is not proven yet and it is previously stated that saline solution (i.e., at low concentrations of 0.5-3%) have not a direct virucidal effect on other virus. However, it enhances the innate immunity system. This effect is mainly arise through the Cl- ions rather than Na+ ions, because Phagocyte myeloperoxidase (MPO) turns Cl- (as well as other halides such as bromide, iodide (Kettle and Winterbourn, 1997; Klebanoff et al., 2013; Kettle et al., 2011)) and hydrogen peroxide into hydrogen hypochlorite (HOCl) in phagosome. Its worthy to be noted that HOCl is the uttermost dominant mammalian germicidal suppresses viruses, probably via chlorination (Ramalingam et al., 2018). MPO is amply presents in neutrophil granulocytes (It is a sub-type of white blood cells) and in lower proportions in other cells such as respiratory system cells whereas an MPO-reliant augment in intracellular HOCl increases antiviral immunity in respiratory system. Therefore, the Cl- augments the antiviral innate immunity of phagocytic/non-phagocytic cells in human respiratory systems. Phagocytes are located in alveolar/airways surface liquid and constantly mobilized Cl- of their vicinities (Ramalingam et al., 2018) subsequently the lack (or scantiness) of chloride could threaten viral inhibition by epithelial cells. Ramalingam et al. (2018) showed that the presence of NaCl can effectively reduce the load of various virus including Influenza A, MHV68 and RSV whilst saline supply enhances mucociliary clearance (Robinson et al., 1997) . NaCl treatment induces cell membrane depolarization, Na+ influx, increased cytosolic Ca2+ and a low energy state (high ADP/ATP ratio), impairing SARS-CoV-2 replication (Machado et al., 2020). Thus, increasing saline availability may be essential to triggering and maintaining antiviral innate immunity in the human respiratory system.

3.2. Nasal/nasopharynx saline irrigations and gargling against the SARS-CoV-2

Performing isotonic/hypertonic saline irrigation against the novel coronavirus was firstly proposed by Farrell et al. (2020) in Washington University. Since there is not a scientific evidence about the effectiveness of saline solutions against the SARS-CoV-2, their conclusion was based on previous studies on saline irrigation (especially hypertonic solutions) that can be helpful against the viral load in nasal and nasopharyngeal. Rosati et al. (2020) were the second research group that proposed the hypertonic saline irrigating of nasal and nasopahrynx as an affordable and even cost-free method that can be used by individuals to reduce the viral load of the SARS-CoV-2 in nasal and nasopahrynx. They reported a single case that used hypertonic saline for irrigation and gargling (3-4% NACL) during the time of quarantine. The patient's RT-PCR tests after 3, 10 and 14 days of the positive test were negative, showing the effectiveness of hypertonic saline. In the ELVIS (Edinburgh & Lothians Viral Intervention Study) center, series of trials are conducted on effectiveness of hypertonic saline nasal irrigating/gargling on patients infected by coronavirus. Their findings indicated that duration of illness in patients which used hypertonic saline irrigating/gargling is nearly 2 days lower (as well as lower symptoms) than those not used the method. They emphasized that these results suggested the hypertonic saline irrigation as an affordable method against SARS-CoV-2, but further trial studies should be performed (Ramalingam et al., 2020). Notably, Suzy et al. (2021) in a review on effectiveness of saline solutions on the nasal and respiratory system was reported that while the saline solution has not a direct effect on the SARS-CoV-2 but it inhibited the viral replication in the respiratory system. Importantly, it is stated that viral replication for an isotonic saline at concentration of 0.9% and 1.5% reduced by around 50% and 100%, respectively (Machado et al., 2020). Casale et al. (2020) suggested the nasal irrigation and oral rinsing with saline solution diminished the viral load in cavities, results in decreasing the rate of transmission as these regions are known as portals for entering the virus. conducted a clinical trial on two groups of patients that 62 of them was study group and 63 patients are controlled group (for comparison) to show the effect of nasal saline spraying/gargling on patients infected by the novel coronavirus. Their findings revealed that the RT-PCR test of 48% of study group are negative while for control group this stand just on 25%. Furthermore, it was revealed that due to the use of saline solution for irrigating/gargling around 91% of the study group showed improvement in inhibiting sever score in their lungs which brings the importance of saline solution irrigation into the spotlight against the SARS-CoV-2. Although utilizing saline solution has not completely realized by scientific community, it was examined that gargling of throat by saline solution can reduce the viral concentration in oropharynx which can consider as a cost-free method against rapid spread of the virus in poor regions with dense population (Tsai and Wu, 2020). It worthy to be noted that the SARS-CoV-2 viral load in nasopharynx swab is higher than oropharynx swab (Wang et al., 2020).

Bradley Field Bale (2020) suggested hypertonic saline gargling/irrigation with 3% concentration to enhance the innate immune system. It consider as a suppression method to prevent the spread of COVID-19 patients without asymptomatic while reducing the progress of infection in early stages. Furthermore, it was reported that throat gargling by warm saline (temperature 56-60°C) at 3% concentration 2-4 times a day results in inactivation of the SARS-CoV-2 (Mukundan, 2019). Panta et al. (2021) also proposed saline gargling and irrigating of nasal as an appropriate therapy against the progress of novel coronavirus. They emphasized that while there is lack of sufficient clinical trials on the effectiveness of saline gargling/irrigating but this method due to its harmlessness nature could implement. Kimura et al. (2020) conducted a clinical trial on non-hospitalized patients that their RT-PCR tests were positive to elucidate the effect of three different saline irrigation solutions which are: hypertonic saline, saline with surfactant, and hypertonic saline with surfactant. Their results elucidated that the efficacy of hypertonic saline irrigation on symptoms and progression of the virus was substantial. Interestingly, early healing of nasal congestion and headache by around 7-9 days was observed in the intervention group. Indeed, using hypertonic and isotonic saline can be consider as the first-line cost-free intervention against the virus for patient in symptomatic and asymptomatic phases.

4. Large-scale desalination technologies

The problem of providing safe drinking due to increasing population size and industrial and social development always consider as a critical issue among governments since it is directly related to human health (Parsa et al., 2020; Sonawane et al., 2022) whereas it anticipated that by 2025 nearly 25% people around the world confronted by severe water shortage (Parsa et al., 2019). The importance of this issue is so vital that it has come up in the last 20 years by several action plans (MDGs and SDGs) in the UN (Parsa et al., 2022, 2020). For decades, mega-scale desalination technologies (RO, MED, MSF, ED) (Parsa et al., 2021) have been used to provide drinking water for large cities mainly near to seas, oceans, and gulfs. Principle of these systems, mechanisms, and their characteristics are presented in previous studies (Burn et al., 2015; Mathioulakis et al., 2007; Khawaji et al., 2008; Gorjian and Ghobadian, 2015; Parsa et al., 2020). Thus, we are not about to discuss each system extensively, instead, a brief explanation about each system presented.

It is of great importance to remind that, besides introducing principles and systems’ mechanism, the main aim of this section is to highlight the temperature of operation (particularly thermally-driven) in various large-scale desalination technologies. Fig. 3 shows the share of desalination technologies through the world.

Fig. 3.

Share of various desalination technologies through the world.

4.1. Multi stage flash (MSF)

The highest share of large-scale thermal desalination technologies in the world is possessed by MSF system. Among two configurations of the MSF plants, the brine recycling approach is more attractive since it recovers a part of rejected heat brine and improves the performance of plant. Briefly, MSF process derived with steam flow that provided by a steam turbine. The steam stream increases the temperature of seawater (feed water) between 90 and 120°C (which defined as the top brine temperature) and the process at the first stage starts (Hanshik et al., 2016; Nair and Kumar, 2013).The number of stages in MSF plants can be up to 40 stages (Nair and Kumar, 2013). After flashing the brine in the first stage, the temperature of leaving brine at the next stage is decreases, subsequently, the pressure of the intended is also decrease to vapor of the seawater at lower temperature.

4.2. Multi effect desalination (MED)

Among thermal desalination technologies, MED plants have remarkable advantages before the advent of MSF systems in 1960. The principle of MED is based on the series of evaporative and condenser chamber that located inside of series of connected vessels known as “effect”. The prominent advantage of MED over MSF is their capability and effectiveness to operate with high saline (such as gulfs water) feed water while it requires less energy per produced water. Briefly, MED process exploited the advantage of using condensation enthalpy of the generated vapor in the previous effect for preceding a new evaporation process in the next effect. This cycle is repeating until the last effect. Generally, MED units worked at low temperature between 60 and 70°C (Zhang et al., 2017; Parsa et al., 2021; Rostamzadeh, 2021; Kariman et al., 2020), however, by utilizing some modifications it can worked at higher temperature up to 125°C (Ortega-Delgado et al., 2017; Zhou et al., 2015).

4.3. Reverse Osmosis (RO)

Mega-scale desalination based on the Reverse osmosis is the dominant method through the world. In some cases RO plants can produce hundreds of thousands cubic meter of drinking water per day. Reverse osmosis is on the basis of membrane process and it not require to alter the phase of feed water. In RO plants, a pressure above the osmotic pressure of solute (saline water) by an external pump applied, which result in passing water from semi-permeable membrane. The concentrate brine remains on the other side. The RO have many configurations and it can be coupled with other thermal desalination systems including MED and MSF. Salinity of the feed is among the most important parameters in RO which can determine the electrical consumption of the pump (Nair and Kumar, 2013). Temperature of operation in RO plants is between 15 and 40°C; however, temperature of water has not a substantial effect on the performance RO plants.

4.4. Electrodialysis (ED)

The Electrodialysis-based desalination is mostly appropriate for lower salinities up to 12000 ppm which usually consider as brackish water. The process is based on the passing impure water between series of anionic and cationic stacks that an electrical field is applied to stacks. Most of existing salts in water being ionic and move to electrodes with opposite electrical charged. The anionic and cationic membranes arrays are arranged continually and a sheet spacer is located between each set of membranes. While the electrodes are charged, the existing anions of water are absorbed by the positive electrode. The anions and cations are moving to the anion-selective and cation-selective membranes respectively. By this configuration, diluted and concentrated solutions are generated in the space between membranes. Eventually, by bounding the spaces by two membranes the cells are introduced in the electrodialysis process. The ED systems are made by hundreds of these cells pair that bounded together with electrodes which called as the membrane stacks (Nair and Kumar, 2013).

4.5. Membrane Distillation (MD)

Another attractive membrane-based desalination technology introduced as membrane distillation (MD) which is thermal-driven separating process. In MDs the difference between temperatures of the both sides of membrane leads to vapor pressure difference which is the driving force of process. Separation of constituents in the MD process is on the basis of liquid-vapor equilibrium. Intrinsically, the term of MD is defined from analogousness of it to traditional distillation process whilst both of them are based on liquid-vapor equilibrium as the basis of molecular separation. Both processes (i.e., MD and traditional distillation) require to enthalpy of vaporization (i.e. latent heat of evaporation) in order to change phase from liquid to vapor. The MD technology has some advantages compare to a dominant membrane-based method such as RO. Importantly, the MD process is not limited by osmotic pressure (because of its thermally-driven nature) and unlike the RO process, this characteristic of MD substantially augmented the water recovery. Temperature of operation in MD would be between 45 and 85°C and increasing the temperature leading to improve the performance of system (Koo et al., 2015; Zare and Kargari, 2018; Shirazi et al., 2014; Hou et al., 2009).

5. Pretreatment methods in desalination technologies

Pretreatment technologies are inseparable part of the all desalination systems whether it is thermal-based or membrane-based. The role of pretreatment is crucial as it can affect the overall performance of desalination plants (Vedavyasan, 2007). The pretreatment process can affect the thermal-based desalination technologies in a way that enable systems to work at higher top brine temperature, results in higher performance (Zhou et al., 2015; Ayoub et al., 2014). Also, in membrane-based systems the pretreatment process lead to reducing the fouling phenomenon in membranes which is one of the most challenges in membrane-based technologies (Zhou et al., 2015). There are various types of pretreatment technologies such as microfiltration, ultrafiltration, nanofiltration (Ju et al., 2020), chlorination, coagulation (Ghernaout et al., 2014), electrocoagulation (Bagga et al., 2008; Zahmatkesh et al., 2022), thermally-treatment, precipitation softening and sometimes combination of these methods. Although an extensive discussion is not necessary about the different pretreatment process, a brief explanation in open literature seems imperative. The mechanism of microfiltration (MF), ultrafiltration (UF), and nanofiltartion (NF) is similar and it defined in differences between their membranes pore size. In this regard, nanofiltration has the highest rate of removing organic and inorganic impurities including chemical compounds and pathogens.

Ebrahim et al. (1997) technically and economically evaluated the microfiltration as pretreatment method for RO and concluded that MF is economically attractive that removes COD and BOD while Lau et al. reviewed integration of the UF as pretreatment method with RO units. They reported that from economic standpoint and quality of water, the UF is an appropriate option but some technical advancement should be carried out on UF to be competitive with conventional methods (Lau et al., 2014). From the beginning of the 21 century, tremendous advances in nanotechnology and developing high-performance membrane, makes the nanofiltration as one of the dominant methods in pretreatment –particularly but not limited- for RO units. Collectively, application of NF as the pretreatment method is wide enough that it can be integrated with all of thermal/membrane-based desalination technologies including MSF, MED, RO, FO, MD, ED, and ion exchange (Zhou et al., 2015). Wang et al. examined the effectiveness of pretreatment by coagulation on the performance of membrane distillation and reported 23% improvement in MD flux (Wang et al., 2008). Friedler and co-workers utilized chlorination as pretreatment method for UF-RO desalination units. Findings indicated that 20 ppm of chlorine results in diminished the bacterial activity while it reduce the fouling of membranes by around 33% (Friedler et al., 2008). Lee et al. realized the effectiveness of chlorination and MF in RO unit against biological fouling (Lee et al., 2010). Heng et al. (2008) showed the effectiveness of combining permanganate with chlorine as pretreatment method against algal bio-fouling in UF membranes while integration of coagulation with UF as pretreatment in RO units lead to removing 98% of algal and microbial contamination (Ma et al., 2007). Furthermore, Yang and Kim (2009) combined coagulation with MF and UF as pretreatment of RO and concluded that coagulation substantially improves the membrane performance, especially, the MF membrane. Hakizimana et al. (2016) experimentally studied the performance of electrocoagulation pretreatment for feed water of a RO unit and reported complete inactivation of microorganisms in feed water. Ayoub et al. (2014) proposed the precipitation softening as the pretreatment method to reduce the scaling in RO units. They utilized NaOH/Na₂CO₃ to alkalized the seawater. The findings at variable PH ranging between 10 and 12 showed more than 99% removal of Mg and Ca elements while complete inactivation of bacteria was also obtained. Gryta (2010) proposed the thermal softening as the pretreatment method of desalination unit. The results showed that increasing the feed water's temperature up to 100°C for 15 min improves the performance of desalination units while it decrease the sedimentation and fouling of membranes. It should be noted that, there are some other pretreatment methods such as ozonation (Oh et al., 2009), utilizing hydrogen peroxide (Lakretz et al., 2018), and UV irradiance (Jin et al., 2018), that consider as advance pretreatment processes and are highly powerful against biological contaminations, however, these methods are not widely used because of economic barriers in some regions. Fig. 4 depicts various pretreatment methods. It is important to mention that some of these pretreatment/ post-treatment methods also applied in wastewater treatment plants (Teymoorian et al., 2021).

Fig. 4.

Various pretreatment methods of desalination technologies.

5.1. Performance of pretreatment methods against various viruses and the SARS-CoV-2

As the SARS-CoV-2 is lethal pathogen, specific and complicated conditions procedures needs for scientific testing which is expensive and time-consuming process. Therefore, pathogen surrogates in some experiments are used instead of dangerous microbes (Lesimple et al., 2020). Generally, viruses due to their small size could be transmitted by vapor, remain airborne, or easily pass through any porous block except the block with extremely tiny pore size. Fig. 5 presents the most common human viruses with respect to their size. Principally, pretreatment methods remove pathogens in contaminated water by damaging to their structure or inhibiting the pathogens to enter to the desalination facilities by filtration. In the context of the ongoing pandemic advance pretreatment methods such as UV and ozonation proposed as appropriate methods against SARS-CoV-2 for water and waste disinfection (Teymourian et al., 2021). For UV, extensive researches highlighted the elimination of the novel coronavirus particularly by UVC wavelengths in different mediums (Raeiszadeh and Adeli, 2020).

Fig. 6.

Membrane water filtration with respect to their pore size. Reprinted from open source (Ostarcevic et al., 2018).

Notably, characteristics of the SARS-CoV-2 which has long single-stranded RNA genomes, naturally, make it tremendously vulnerable for UV wavelengths (Avila et al., 2020). Although the number of studies on direct effect of UVC on SARS-CoV-2 in aqueous solution is rare, high energy photons of UVC wavelengths (Specifically in regions 260-265 nm) are highly destructive to cells because of highest UV absorption by nucleic acid. However, Robinson et al. in a preprint and Ma et al. in research paper similarly elucidated that UVC wavelengths can completely eliminate SARS-CoV-2 in aqueous solution (Robinson et al., 2021; Ma et al., 2021). Furthermore, ozonation consider as a powerful method against both enveloped and non-enveloped viruses by direct ozone impact and/or indirect effect by generating free radicals such as ·OH, O₂·-, and H₂O₂ (Murray et al., 2008). The other prominent advantage of ozonation is the synergistic effect of ozone reaction and generated ROSs with pathogen's constituents such lipid, protein, and amino acid which results in producing other highly oxidative radicals such as RCOO· in chain-like reactions that boost effectiveness of ozonation process against pathogens (Tizaoui, 2020). Chlorination is another disinfection method that widely applied during the pandemic. Fernando et al. in an extensive review highlighted the critical role of chlorine for removal of the SARS-CoV-2 regarding the pros and cons of the method (Robinson et al., 2021). The aforementioned methods mainly eliminate the SARS-CoV-2 by damaging to the fragile outer surface of the virus, while in filtration process such as MF, UF, and NF the tiny pore size of membranes rejected the virus. Approximately, the designed pore size (pz) ranges for MF, UF, and NF between 0.1<pz<10 µm, 0.5<pz<0.01 µm, and 5<pz<10 nm, respectively. Notwithstanding of emerging NF as an effective method for pathogens removal, UF is at the forefront of membrane-based pretreatment method; particularly for RO (Lesimple et al., 2020). Al-Aani et al. (Al-Aani et al., 2023) comprehensively reviewed the application of UF for wastewater treatment plant and reported high-reliability of UF for removing pathogens in contaminated water particularly viruses and bacteria. Since the pore size in NF is less than 10 nm, none of the aforementioned human viruses (depicted in Fig. 5 ) can cross the NF membranes. This makes NF pretreatment as completely reliable method against pathogens specifically viruses (Lesimple et al., 2020). Furthermore, effectiveness of the NF for a broad range of waterborne pathogens including bacteria, viruses, and protozoa have been extensively reported (Singh et al., 2020). Meanwhile, Venugopal et al. (2020) proposed to utilize electrospun NF fiber membrane not as the pretreatment method but as a monitoring tool for early detection of an unusual accumulation of microorganism (in this case SARS-CoV-2) in water bodies entering to water treatment plants. Fig. 6 shows various membranes pore size for water filtration.

Fig. 5.

Common human viruses with the relative size. Reprinted from open source (S.Io.B.S. Viralzone 2020).

6. Are mega-scale desalination technologies safe during the pandemic?

Reliability of desalination technologies in the era of COVID-9 still remained unanswered. In this section based on their principles, feasibility and safety of these systems during the ongoing pandemic is discussed. It should be point out that all discussions in this section are based on the medical evidence, clinical trials, laboratory facts, and actual principle of the water desalination technologies. In this regards, an extensive discussion in three sections which are, the impact of feed water's salinity (evidence of nasopharynx/nasal saline solution irrigation/gargling), temperature of desalination technologies, and pretreatment processes to realize the reliability of desalination plants are presented.

6.1. Translation of nasal/nasopharynx saline irrigation and gargling in reliability of desalination technologies (Effect of salinity)

As we previously discussed nasopharynx, throat, and nasal irrigation and gargling by hypertonic and isotonic saline solutions proposed as a preventive method that even it not eliminated the virus, it inhibits of replicating the SARS-CoV-2 in its portals. Furthermore, it was stated that NaCl solutions, especially hypertonic saline solutions that defined with NaCl concentration higher than 0.9% (NaCl>0.9%) is more preferable as the first-line intervention against the SARS-CoV-2. Some researchers used hypertonic saline at higher concentration of 1.5% up to 4% (Machado et al., 2020; Rosati et al., 2020). Clinical trial conducted on the saline irrigating/gargling approach (especially ELVISE researcher) and all of them pointed out the effectiveness of salinity on reducing the viral (i.e., SARS-CoV-2) load and inhibiting viral replication in the nasal, nasopharynx, and throat. It is worthy to be reminded that in a meta-analysis it was elucidated that sing hypertonic saline nasal irrigation (less than 5%) shows greater effectiveness than isotonic saline solution for seasonal pathology (Kanjanawasee et al., 2018). On the other hand, feed water of all desalination plants utilized by seawater, oceans and gulfs. Salinity of these water sources may be varied but generally salinity of feed water in all studies is taken as 35000 ppm. Many of these water resources such as the Persian Gulf, Mediterranean Sea, Pacific Ocean, Indian Ocean to name a few, are the home for most of desalination plants throughout the world and have salinity higher than 35000 ppm or 3.5%. Table 1 shows some of the most well-known water bodies with respect to their salinity.

Table 1.

Water bodies with respect to their salinity.

Water Body	Continent	Salinity (ppm)	Common Type of Desalination
Persian Gulf	Asia	40000–41000	RO,MED,MSF,MD
Mediterranean Sea	Europe/Africa/Asia	38000–40000	RO,ED
Pacific Ocean	All except Arica	32000–37000	RO
Indian Ocean	Oceania/Asia	32000–37000	RO

In this regard, the first preventive factor in safety of the large-scale desalination plants is the salinity of feed water. This is not just an assumption but it can be concluded based on concrete pieces of evidence of medical experts’ experiments. When in a small region such as nasal, nasopharynx, or throat with high load of viral RNA the replication process can be inhibited by hypertonic saline, in large saline environments such as seas, oceans, and hyper-saline gulf's waters, replication and the load of the SARS-CoV-2 drastically decreases. Herein, there is an important factor about the minimum infected dose (MID) of disease. Generally, MID can define as the minimum load of pathogen that can lead to the disease. Pathogens have different MIDs which means below the certain MID of pathogen, the disease (or symptoms) will not be appeared in the body. Among pathogens, viruses has higher MID due to their simple structure and higher replication rate compare to bacteria, protozoa, and fungi which justifies why viruses are highly infectious rather than other pathogens. In the case of the novel coronavirus, it seems that the MID of the virus is very low because of high rate of transmission through the world. This fact is justified by its new variants that are more contagious than the previous variants. Nevertheless, researchers in clinical trials observed that the hypertonic saline irrigating/gargling reduce the viral load, reduce symptoms, and length of recovery. It means that presence of NaCl reduces the infection dose of the SARS-CoV-2. By taking into consideration of all the above mentioned discussion, salinity of feed water in large-scale desalination systems is a factor that can inhibited the feed water and the structure of desalination plant gets contaminated. However, some questions are remained unanswered in this context such as the effect seawater salinity on the eliminating the SARS-CoV-2 or the effect of salt concentration on viability of the SARS-CoV-2 with respect to the time.

6.2. Temperature of operation

One of the most important factors that highly affected the survival of SARS-CoV-2 in different environment is temperature. It was showed that viability of the virus has reverse relationship with temperature. While the virus can be survived in temperature of 4°C for almost two weeks (Chin et al., 2020) it completely inactivated at temperature 56°C in 30 min (Wang et al., 2020). Fig. 7 shows the effect of temperature on the viability of the SARS-CoV-2 (the T₉₀ which defined as the time for eliminating 90% of viral concentration) virus in various water matrices (a detail explanation is presented in our previous study (Parsa, 2021)) in temperature range of 4–37°C (Ahmed et al., 2020). Furthermore, Fig. 8 illustrated the inactivation of the virus by increasing the temperature in a range between 55 and 90°C (Batéjat et al., 2021). Indeed, the rate of survival and viability of the virus by increasing the temperature of environment exponentially diminished. On the other hand among the aforementioned desalination technologies the two membrane-based RO and ED are worked on the basis of different pressure and ion-exchange and temperature has not play a significant role in the process while the MED, MSF, and MD are thermally-driven technologies and temperature role is vitally important for performance of the system.

Fig. 7.

The average T90 of the SARS-CoV-2 in various water matrices (Ahmed et al., 2020).

Fig. 8.

Time for Inactivation of the novel coronavirus by increasing temperature (Batéjat et al., 2021).

Among these three technologies, MSF working temperature is higher than 95°C and it can gets up to 120°C. Likewise, MED range of temperature is varied and it can work at lower top brine temperature as low as 60-70°C but it has potential to work at higher temperature as high as 120°C. Furthermore, the MD process usually driven at temperature higher than 50°C and it worked as high as 85°C. Considering all of the above mentioned range of temperatures for thermally-driven desalinations and susceptibility of the SARS-CoV-2 to temperature regarding Fig. 8, the MSF desalination units has the highest temperature of operation which indicated this fact that the SARS-VoV-2 cannot remain survive in such hot environment and it will be eliminated during the process. Similarly, the same can be concluded for MED units since it can operate at higher temperature up to 120°C. Although the MED units also can worked at lower temperature between 60 and 70°C but this temperature range is not high risk for the plant since the viral in such temperature range completely inactivated between 15 and 5 min. Thus, the feed water and plant structure would not contaminated by the virus due to thermal inactivation. For MD systems, however, the temperature of operation is not as much as high of MSF or MED and it can work at lower temperature such as 50°C or even lower. Thus, for MD desalination units in the temperature operation higher than 55°C the feed water and the unit will not prone to be contaminated because the SARS-CoV-2 will eliminated in less than 30 min, but at lower temperature of operation (i.e. 45–55°C) (Parmar et al., 2021) the inactivation of the SARS-CoV-2 is unknown in the feed water and post-treatment may need to be consider.

6.3. Effectiveness of pretreatment processes

As it discussed before, pretreatment process is somehow a mandatory part of any desalination technology which utilized to increase the performance of units while it maintains equipment of units from negative effects such as corrosion and so on. Among the available pretreatment process, filtration, especially, NF is widely proposed as a powerful method due to it highly efficacy in separation even particles at nanoscales. On the other, MF and UF also can be used as antibacterial pretreatment methods but for pathogens such as viruses that have particle size is in nanoscale range, MF and UF may not be effective enough. On the other hand, NF can be consider as an strong against biological contamination even viruses with particle size of 10-100 nm since NF membrane usually has pore size between 0.2 and 10 nm (Ostarcevic et al., 2018; Chuntanalerg et al., 2018). Thus, NF is a powerful method against the SARS-CoV-2 which its particle size is in the range of 60-140 nm. However, using nanofiber membrane for removing the SARS-CoV-2 in wastewater was proposed during the ongoing pandemic (Venugopal et al., 2020). The other pretreatment method is chlorination which always is considered as one of the disinfection methods in wastewater treatment plants. Chlorine compounds consider solely or in combine by other pretreatment methods such as MF (Lee et al., 2010). It was reported that nearly 20 mg/L of chlorine is effective enough to eliminate SARS-CoV-1 (Wang et al., 2005). Therefore, pretreatment by chlorine compounds can be consider the other powerful pretreatment methods against biological contamination, including the SARS-CoV-2. Meanwhile, some pretreatment methods such as precipitation softening may also effective in inactivation of the SARS-CoV-2 since they work at near-extreme pH range higher than 12. Interestingly, it was examined that the SARS-CoV-2 lost infectivity in extreme pH level of 2-3 and 11-12 after 1 day (Chan et al., 2020). Thermal pretreatment also consider as one of the most suitable methods against biologically-contamination feed water since many pathogens are susceptible to increasing temperature including SARS-CoVs. The method that proposed by Gryta (Gryta, 2010) which was based on increasing temperature of water to boiling point can be effective against many bacteria and viruses. Importantly, extensive discussion on performance of pretreatment methods against the novel coronavirus and other pathogens in section 5.1 indicated that pretreatment methods also act as the first-line preventive factor against the biologically-contaminated water in desalination plants. Fig. 9 illustrated a flowchart that depicts the approach of this review.

Fig. 9.

Flowchart of the present study.

7. Concluding remarks and future studies

Based on the above discussion the following can be summarized:

• •A high large number of infections results in contaminated of water bodies because of wastewater and human urine and excreta.
• •Various types of pathogens including the SARS-CoV-2 contaminated the water media.
• •The SARS-CoV-2 can remain viable in various water matrices at low temperature and proper conditions.
• •The novel coronavirus is tremendously susceptible to increasing the temperature of its environment whereas the survival of the virus by increasing temperature is exponentially decreases.
• •The novel coronavirus in temperature of 56, 65, and 95°C eliminated in 30, 15, and 3 min, respectively.
• •Based on clinical trials saline irrigation/gargling (especially hypertonic saline) of nasal/nasopharynx/throat lead to prevent virus replication and decrease symptoms and reduce the length of illness.
• •The salinity of mega-scale desalination technologies is equal or higher than hypertonic saline (>35000 ppm) solution which means by presence of the novel coronavirus in feed water the risk of its viability is very low.
• •Temperature of operation for MSF, MED, and MD is between 90 and 120°C, 60 and 125°C, and 45–85°C, respectively.
• •Among thermally-driven desalination technologies temperature operation of MSF and MED are very high for survival of the SARS-CoV-2 which means presence of the SARS-CoV-2 in feed water could not lead to contamination of produced water as well as structure of desalination plants.
• •MD units can work at low and medium temperature ranges, thus in the case of the medium working temperature between 55 and 85°C the structure of system and produced water could not contaminated but at lower temperature of operation (45-55°C) contamination of feed water may have risks for unit and produced water.
• •Various pretreatment methods such as filtration, chlorination, thermal/precipitation softening, UV irradiance, ozonation, and hydrogen peroxides can prevent the transmission of biological contamination (including the SARS-CoV-2) in feed water.
• •Chlorination and its combination by other methods such as MF, UF and coagulation can be consider as an effective method to decrease the biological contaminated since the use of chlorine compounds for eliminating then SARS-CoV-1 is proven before.
• •Among pretreatment methods, nanofiltration membrane is the most emerging technology because of its effective separation and wide application in integrating with all of the large-scale desalination technologies.
• •The pore size of the nano-filter membranes is between 0.2 and 2 nm which means it can inhibit transmitting most of pathogens including the SARS-CoV-2 because of particle size of 60–140 nm.
• •The RO units as the dominant method in large-scale desalination technologies are pretty reliable because of various pretreatment methods among them nanofiltartion membranes as the most preferable method.
• •Some pretreatment methods such as UV, H2O2, Ozonation are among the powerful methods to eliminate the SARS-CoV-2 but they are rarely used as the pretreatment because technical and economical limitations.
• •ED units are not work at high temperatures neither with high salinity water and the units usually is more preferable for low-saline water (brackish water) up to 12000 ppm, therefore the in the case of contaminated feed water by the SARS-CoV-2 it is not clear how could be the performance of the system.
• •Survival and viability of the SARS-CoV-2 in different seawater and gulfs with respect to time is an interesting topic worthy to be examined.
• •Effect of salt concentration in seawater on the survival of the SARS-CoV-2 is another topic that could be consider by medical researchers and environmental engineering experts.
• •Evaluation of the synergistic effect salt concentration with increasing temperature of solution is also an interesting topic worthy to be realized.

8. Conclusion

The ongoing pandemic affected the whole world from different aspects. One of the most barriers of this situation is drop on the shoulders of environment. The high number of infections results in contaminated of water bodies by wastewater and sewage. The high load of viral in water bodies has too many risks to open a new window for transmission of the virus. Although during the COVID-19 the respiratory system is the predominant route of transmission, but it is not the only path of spreading the virus.

In the present study reliability of large-scale desalination technologies during the COVID-19 pandemic is discussed. Five desalination systems that has the highest share of commercial markets are examined. Three important parameters have stepped into spotlight to evaluate the safety of these systems in producing drinking water without biological contamination. The first parameter was salinity of the feed water which it showed that based on medical facts and clinical trials saline solution (especially hypertonic saline) is preventive factor in growing the SARS-CoV-2, indicating that the feed water of large-scale desalination technologies is a not proper environment for the virus to remain viable or replicate. The second factor was temperature of operation in thermally-driven desalination technologies which it is showed that the high temperature of operation for thermal-driven desalination technologies is inhibited the virus to remain infected since the SARS-CoV-2 is highly vulnerable to increasing the temperature. The third preventive factor against biological contamination of feed water was implementing various pretreatment methods especially for RO units. It was revealed that the pretreatment methods especially nanofiltration are powerful method that can eliminated pathogens before entering the feed water to desalination unit.

Eventually, based on the aforementioned discussion, it can be concluded that the large-scale desalination technologies is safe enough during the ongoing pandemic, even if the feed water of the unit is contaminated by the virus. It worthy to be noted that the approach of the present study is not limited to the COVID-19 pandemic but it is true for similar situation in the future whereas the water bodies are contaminated and the pathogen (i.e. most viruses) is susceptible to temperature.

Funding Information

This review has not received funding from any organization

Declaration of Competing Interest

The author declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

• Data will be made available on request