A critical assessment of SARS-CoV-2 in aqueous environment: Existence, detection, survival, wastewater-based surveillance, inactivation methods, and effective management of COVID-19

In early January 2020, the causal agent of unspecified pneumonia cases detected in China and elsewhere was identified as a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and was the major cause of the COVID-19 outbreak. Later, the World Health Organization (WHO) proclaimed the COVID-19 pandemic a worldwide public health emergency on January 30, 2020. Since then, many studies have been published on this topic. In the present study, bibliometric analysis has been performed to analyze the research hotspots of the coronavirus. Coronavirus transmission, detection methods, potential risks of infection, and effective management practices have been discussed in the present review. Identification and quantification of SARS-CoV-2 viral loads in various water matrices have been reviewed. It was observed that the viral shedding through urine and feces of COVID-19-infected patients might be a primary mode of SARS-CoV-2 transmission in water and wastewater. In this context, the present review highlights wastewater-based epidemiology (WBE)/sewage surveillance, which can be utilized as an effective tool for tracking the transmission of COVID-19. This review also emphasizes the role of different disinfection techniques, such as chlorination, ultraviolet irradiation, and ozonation, for the inactivation of coronavirus. In addition, the application of computational modeling methods has been discussed for the effective management of COVID-19.

• High concentrations of SARS-CoV-2 in wastewater have been reported globally. • Viral shedding via stool and urine are the primary route for SARS-CoV-2 in water. • WBE is an effective tool for early detection and assessment of COVID-19. • Inactivation of SARS-CoV-2 by disinfection is found to be effective. In early January 2020, the causal agent of unspecified pneumonia cases detected in China and elsewhere was identified as a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and was the major cause of the COVID-19 outbreak. Later, the World Health Organization (WHO) proclaimed the COVID-19 pandemic a worldwide public health emergency on January 30, 2020. Since then, many studies have been published on this topic. In the present study, bibliometric analysis has been performed to analyze the research hotspots of the coronavirus. Coronavirus transmission, detection methods, potential risks of infection, and effective management practices have been discussed in the present review. Identification and quantification of SARS-CoV-2 viral loads in various water matrices have been reviewed. It was observed that the viral shedding through urine and feces of

Introduction
In late 2002, unidentified cases of life-threatening respiratory disease were reported in Guangdong province, China, followed by reports from Canada, Vietnam, and Hong Kong. In March 2003, the World Health Organization (WHO) declared severe acute respiratory syndrome coronavirus (SARS-CoV) was the causal agent for the disease and declared a global pandemic at the end of March 2003 (Ksiazek et al., 2003;WHO, 2003a). According to the WHO, SARS-CoV is an airborne virus mainly transmitted directly via tiny saliva droplets as a virus carrier, similar to a cold or flu, and indirectly via touching infected surfaces (fomites) (WHO, 2003b). In contrast, only a few studies suggested that water and wastewater may be a source of the transmission of SARS-CoV (Gormley et al., 2017;Wang et al., 2005a). After sixteen years, the coronavirus disease 2019 , engendered by the novel SARS-CoV-2, emerged in December 2019 in Wuhan, Hubei province (China) (WHO, 2020). The COVID-19 disease spread rapidly in over 200 countries worldwide, with 621,325,855 confirmed cases and 6,543, 103 deaths recorded as of September 28, 2022 (Worldometer, 2022).
One of the members of the coronaviridae family is SARS-CoV-2, which is genetically identical to the SARS-CoV and belongs to the same coronavirus genera, i.e., Beta coronavirus. (Mariano et al., 2020;Patel et al., 2021). The SARS-CoV-2 virion consists of an inner core of positive single-stranded ribonucleic acid (ssRNA) and the nucleocapsid (N) protein, and an exterior protein shell, commonly known as the capsid, which contains three main structural proteins, including spike glycoprotein (S), membrane protein (M), and envelope protein (E), as depicted in Fig. 1 (Mariano et al., 2020). SARS-CoV-2 is classified as an enveloped virus due to an extra lipid bilayer membrane surrounding the protein capsid, which is structurally and functionally distinct from the non-enveloped viruses which lack this lipid bilayer membrane (Louten, 2016). The lipid membrane of the enveloped viruses, including SARS-CoV-2, allows them to exit using host cellular machinery and increases the virus particle packaging capacity with the additional viral proteins. Further, they hide the structurally restricted capsid antigen from freely circulating antibodies, thus has more structurally flexibility and make a stronger impact on their detection and persistence in the aqueous environment Wisskirchen et al., 2014).
The sudden increase in the occurrence of SARS-CoV-2 in the environment has resulted in a quick spread of the COVID-19 pandemic across the world (Patel et al., 2021). Meanwhile, SARS-CoV-2 RNA shedding by an individual via urine and feces raises concerns that COVID-19 may also spread through water and wastewater (Liu et al., 2021;Tran et al., 2021). Some studies have confirmed the spread of coronavirus across the apartments and within the communities due to daily human activities and wastewater plumbing systems (Gormley et al., 2017;Patel et al., 2021). This must be thoroughly investigated and analyzed as a potential mechanism of COVID-19 spread which could result in community-wide transmission. Furthermore, due to the lack of suitable treatment systems, untreated wastewater is often discharged directly into surface water in many low-income countries Mubedi et al., 2013). SARS-CoV-2 in these wastewaters could contaminate surface water and pose serious health hazards to humans (Kasloff et al., 2021).
The occurrence of SARS-CoV-2 in sewage systems can be assessed using wastewater-based epidemiology (WBE), also known as sewage surveillance (Huizer et al., 2021;Li et al., 2022;Mandal et al., 2020). WBE can be a valuable technique for estimating the viral spreading risk at target locations (Kumar et al., 2020). As a result, the existence of SARS-CoV-2 in different water matrices can become an important aspect of research (Daughton, 2020). Several studies have already been published on the detection and persistence of SARS-CoV-2 in various environmental matrices (Kasloff et al., 2021;Kolarević et al., 2021). However, there has been little credible evidence about their persistence in aqueous environments, which might be regarded as a possible mode of transmission (Doremalen et al., 2020;Liu et al., 2021). Although coronaviruses are fairly easy to inactivate than non-enveloped viruses, however, a sudden rise in the concentration in water matrices may necessitate a high concentration of disinfectants Fig. 1. Basic structure and genome of SARS-CoV-2 (coronavirus).
V.K. Parida et al. (chlorination)/extensive energy input in the case of ultraviolet (UV) or heat treatment (Carraturo et al., 2020;Patel et al., 2021). Therefore, additional research is required to understand the aftereffects of employing a higher concentration of disinfectants. This paper presents an overview of the currently known SARS-CoV-2 in different environmental matrices, mainly aquatic environments. The prime objective of this review is to give a new perspective on the standard analytical steps employed to detect SARS-CoV-2 in different water matrices, its persistence, probable transmission, and the different disinfection techniques applied for its inactivation. This review also focuses on the application of WBE or sewage surveillance in the early detection of COVID-19 cases in various target locations worldwide. In this context, a correlation analysis of viral load detected in different countries with average active COVID-19 cases reported worldwide was also undertaken in this review. In addition, a bibliometric analysis was conducted to comprehend the present state of SARS-CoV-2 research worldwide. The later section of the study includes the SARS-CoV-2 effects on the community and measures taken by various countries to ensure effective wastewater management. The application of various computational modeling approaches for effectively handling COVID-19 has also been discussed in this review.

Methodology
The database from the Scopus platform was retrieved to perform statistical analysis to understand the COVID-19 publication scenario. The online database of Scopus was accessed on 3 rd February 2022. The articles related to COVID-19 have been searched using keywords like ["COVID-19 ′′ OR "Coronavirus disease 2019 ′′ OR "COVID-2019 ′′ OR ′′ 2019-nCoV" OR "nCov-2019 ′′ OR "SARS-COV-2 ′′ OR "Novel Coronavirus" OR "Severe acute respiratory syndrome coronavirus 2 ′′ OR "HCoV-19"] AND ["wastewater" OR "water" OR "municipal wastewater" OR "sewage" OR "hospital wastewater" OR "surface water" OR "domestic wastewater"]. Only the research and review articles from 2019 to July 2022 were considered for the bibliometric analysis. The search results were exported in CSV format, including keywords, citations, and bibliographic information. A manual screening was then performed to discard duplicate articles or articles unrelated to the topic. Finally, 3745 relevant articles were chosen for performing the bibliometric analysis.

Current publication scenario on COVID-19
The research on COVID-19 and related topics has only recently begun following the outbreak of the global coronavirus pandemic. Many V.K. Parida et al. articles have already been published on these topics. However, the literature on their transmission mode via water and wastewater is limited. Fig. 2(a) represents the year-wise publications of articles on COVID-19 by different countries. The total number of articles published worldwide in 2020 was 704, which gradually increased to 1714 in 2021 and 1326 in July 2022 and may continue to increase in the coming years. The statistical analysis concerning the number of publications per year from different countries was carried out using Microsoft Excel. Fig. 2(a) shows that the USA has the highest number of articles published, with 902, followed by India, with 499.
The Scopus database was then imported into the VOSviewer (1.6.17, Leiden University, Netherlands) software for bibliometric mapping (VOSviewer, 2022). The nodes connected with various network links represent the visualization. The size and spacing between these nodes represent the terms' significance and dependency, respectively. The emerging topics and research trends can be easily identified with the help of visualization maps. Co-authorship and co-occurrence analysis of the data has been presented in the current study. The details regarding co-authorship and co-occurrence analysis used to carry out the recent trend analysis are briefly discussed in section 1.1 of the supplementary material. From Fig. 2(b), it can be observed that among the countries that have published articles on COVID-19, the USA has the highest number of publications, followed by India and China. The USA has 68 collaborators, suggesting a strong link in co-authorship with other countries.
The network visualization map of keywords on COVID-19 has been shown in Fig. 2(c). The keyword "COVID-19" was highlighted since it was the most occurred keyword and had the highest number of connected points (Fig. 2(c)). The VOSviewer software divided and classified the keywords into 4 different clusters (red, blue, green, and yellow), which showed the relationship between the topics. The red cluster mainly includes the keywords related to prevention and control measures taken for COVID-19, such as masks, soap, sanitizers, handwashing, hygiene, etc. (Fig. 2(c)). The blue cluster is mainly comprised of keywords related to WBE, such as water sampling and monitoring, wastewater treatment, virus load, etc. (Fig. 2(c)). The keywords, such as aerosols, water pollution, air pollution, lockdown, etc., related to the risk assessment of coronavirus, are clustered under the green section ( Fig. 2(c)). Finally, the yellow cluster contains the keywords associated with the study of the biology of viruses, such as virology, genetics, molecular docking, etc. (Fig. 2(c)). Fig. 2(d) represents the density visualization of the keywords on COVID-19. A rainbow color pattern has been chosen, where high density is denoted by red, while low density is denoted by blue. COVID-19 and humans form the two major hotspots, as indicated by the red color ( Fig. 2(d)). The yellow color of the neighboring points indicates a high correlation with the hotspots (Fig. 2(d)).

Detection and existence of SARS-CoV-2 in the aqueous environment
Municipal wastewater (MWW) and hospital wastewater (HWW) host a variety of pathogens, including SARS-CoV-2, which are considered one of the critical sources for numerous pathogenic diseases, along with COVID-19 (Kumar et al., 2022;Parida et al., 2022). Detection and quantification of SARS-CoV-2 in an aqueous environment are crucial for approaching WBE accurately (Huizer et al., 2021). According to previous studies, SARS-CoV-2 genetic material becomes diluted, and its concentration level decreases as the detention time in the wastewater collection systems increases (Ahmed et al., 2020a;Medema et al., 2020). Due to its low prevalence in the aqueous environment, various pre-analysis steps are performed on the samples to ensure the possible identification of SARS-CoV-2 RNA (Patel et al., 2021). Standard viral analysis in water and wastewater includes various steps, i.e., (a) sample collection, (b) sample preservation, (c) sample preparation, (d) sample extraction, and (e) sample detection and quantification (Nemudryi et al., 2020;Tran et al., 2021). The standard analytical steps for the detection and quantification of SARS-CoV-2 in the samples collected from different water matrices have been depicted in Fig. 3. These steps should be conducted carefully and under expert supervision, because even slight errors during the analysis can influence the results.
The initial step for SARS-CoV-2 analysis begins with collecting and preserving samples through grab or composite sampling (Ahmed et al., 2020a;Nemudryi et al., 2020). In most cases, the wastewater samples were collected in plastic bottles or bags of varying collection volumes, i. e., typically 0.2-2 L. The samples were instantly placed in dark ice boxes (~4 • C) and transported to a nearby laboratory for RNA extraction (Ahmed et al., 2020a;Haramoto et al., 2020). The next step in the viral analysis is sample concentration, which is used to isolate viruses from large cell debris and other small molecules in aqueous samples. This step primarily assists in avoiding the effect of dilution in water samples, allowing for easier detection via polymerase chain reaction (PCR)-based testing (Payne, 2017). However, first, the samples should be processed or pre-conditioned to improve the overall viral concentration efficiency (Bofill-Mas and Rusiñol, 2020;Patel et al., 2021). Some of the usual pre-conditioning steps include pH balancing followed by adjusting salinity and filtration (Bofill-Mas and Rusiñol, 2020). To enhance virus extraction, different conditioning agents, such as AlCl 3 , MgCl 2 , and glycine, have been used (Bofill-Mas and Rusiñol, 2020). Subsequently, the viral concentration techniques, such as electronegative or electropositive virus adsorption-elution (Cashdollar and Wymer, 2013), polyethylene glycol (PEG) precipitation (Ahmed et al., 2020b), skimmed-milk flocculation (Calgua et al., 2013), ultrafiltration (Cashdollar andWymer, 2013), and ultracentrifugation (Haramoto et al., 2018), have been used. These techniques have been effectively applied for concentrating SARS-CoV-2 in water and wastewater samples (Table S1).
RNA extraction is another vital step followed by viral concentration. Virus RNA is extracted and purified from the concentrated sample without inflicting any damage ( Fig. 3) (Lever et al., 2015;Peirson and Butler, 2007). Previously, the most commonly used techniques performed for virus RNA extraction were organic extraction by guanidinium thiocyanate-phenol-chloroform solutions, silica membrane spin column technology, and magnetic separation technology (Tavares et al., 2011). However, RNA samples extracted by these techniques are usually contaminated with proteins, genomic materials, and chemical solvents, including phenol, ethanol, and salts (Tavares et al., 2011). Recently, different commercially available RNA extraction kits have been used to extract SARS-CoV-2 RNA from sewage samples (Table S1). The main advantages of these kits over traditional methods are their low cost, no need for toxic solvents, and ability to produce whole intact RNA with little contamination of protein and other biological components (Sapmag, 2022;Tavares et al., 2011).
The final step of viral analysis is performed by conducting PCR-based tests on the virus-concentrated samples in the laboratory. The positivestranded RNA virus, i.e., SARS-CoV-2, can only be detected through reverse transcription (RT) of RNA into deoxyribonucleic acid (DNA) followed by amplifying the specific DNA targets using PCR. Whereas, to measure the concentration of SARS-CoV-2 DNA in water and wastewater samples, the RT-quantitative real-time PCR (RT-qPCR) method is generally used (Fig. 3) (Freeman et al., 1999;L. Zhang et al., 2021). PCR-based techniques are quick, accurate, and can detect up to five targets at the strain level in a single assay (Patel et al., 2021). Recently, studies from India, the USA, Spain, China, Australia, France, etc. have employed several designed RT-qPCR assays to detect and quantify SARS-CoV-2 in water and wastewater samples (Ahmed et al., 2020a;Kocamemi et al., 2020). For instance, Medema et al. (2020) reported one of the earliest detections of SARS-CoV-2 in sewage samples in the Netherlands. The samples collected from six major cities were tested using four RT-qPCR assays. When the incidence of COVID-19 increased in these cities in March 2020, the RNA signal detected by the RT-qPCR assay (N1-N3 genes) increased up to 2200 gene copies/mL (Medema et al., 2020). A few studies regarding the detection and existence of SARS-CoV-2 in the aqueous environment are briefly discussed in section 1.2 of the supplementary material.

Persistence of SARS-CoV-2 in the environment
Virus persistence/survival in an environment is critical for its transmission. Previously, much literature has reported on the survival of SARS-CoV RNA in various environmental matrices, including water, wastewater, soil, metals, paper, cloth, etc. (Gundy et al., 2009;Kasloff et al., 2021). However, only limited evidence exists on the persistence of SARS-CoV-2 in water matrices (Doremalen et al., 2020;Kasloff et al., 2021). As reported in the earlier literature, the persistence of SARS-CoV and SARS-CoV-2 in various water matrices can be considered a reference for comparison (Table S2).

SARS-CoV-2 RNA survival in various environmental matrices
Recently, Kasloff et al. (2021) selected different personal protective equipment (PPE) commonly used by medical staff and the general public during the ongoing pandemic to check the persistence of SARS-CoV-2 on these PPEs. The results indicated the presence of SARS-CoV-2 RNA on face shield plastic and N-95 mask for up to 21 days, 14 days on Tyvek, 7 days on nitrile gloves, and roughly 4 h on cotton fabric at 20 • C with RH ranging from 35 to 40% (Table S2). The study also suggested the importance of appropriate handling of PPE in high-risk infected areas and the possible use of cotton, particularly cotton masks, since viral persistence on cotton surfaces was lower than on other characters to control COVID-19 transmission (Kasloff et al., 2021). Likewise, Ye et al. (2016) examined the stability of two human-enveloped viruses, namely murine hepatitis (MHV) coronavirus and Pseudomonas phage cystovirus (φ6), in raw MWW before any secondary treatment. The results indicated the estimated time required for reaching 90% inactivation of MHV and φ6 is about 7-13 h at 25 • C, which is the usual summer temperature of wastewater. Both viruses could survive for up to 28-36 h at 10 • C, which is the average winter temperature of sewage. The study also reported human enveloped viruses discharged via feces could reach the wastewater treatment plants (WWTPs) in an active condition, particularly during the winter season, since the typical hydraulic retention time for wastewater treatment systems is generally 24 h (Ye et al., 2016). However, the survivability experiments in these studies were carried out in a laboratory in a controlled environment, whereas the survivability of SARS-CoV-2 in the natural environment may differ. The laboratory experiment may not accurately represent the virus's behavior in the natural environment. Therefore, it is crucial to understand the behavior of SARS-CoV-2 alongside its potential to spread in the aquatic environment. More research is needed to understand the factors influencing SARS-CoV-2 survival in the aquatic environment, such as pH, V.K. Parida et al. temperature, salinity, and other microorganisms. Furthermore, research should focus on the possibility of SARS-CoV-2 spreading through WWTPs and the potential for transmitting the virus to humans through contact with contaminated water.

Major influencing factors for the coronavirus survival
The survival of coronaviruses in an environmental matrix is dependent on a variety of parameters such as the kind of environmental matrix (e.g., land, water, and air), the type of virus, temperature, humidity, pollution level, ultraviolet radiations, and others (Achak et al., 2021;Tosepu et al., 2020). Gundy et al. (2009) evaluated the existence of human coronavirus 229E in unfiltered and filtered tap water samples at 23 • C and 4 • C, respectively. The study reported that temperature, organic matter concentration, and predatory microorganisms like protozoa are the major influencing factors in coronavirus inactivation in test water samples. The time required for a 99.9% reduction of coronavirus titer from test water samples was about 10 days at 23 • C. While at 4 • C, the coronavirus inactivation rate becomes slower and can survive for up to 100 days (Table S2). Likewise, another study evaluated the persistence of SARS-CoV in human stool and urine samples. The results showed that at 20 • C, SARS-CoV only lasted for 3 days in the stool samples but survived for 17 days in the urine samples (Wang et al., 2005b) (Table S2). The possible reason could be that the fluids contain salts, which can help sustain osmotic pressure for the survival of the virus. Furthermore, the presence of chemicals, including detergents, in the wastewater can damage the viral envelope, which can be a significant factor in the survival of coronavirus in wastewater (Gundy et al., 2009). Recently, Chowdhury et al. (2020) performed an experiment using Fuzzy logic approach based on artificial intelligence (AI) system to evaluate the importance of different environmental conditions responsible for the survival of SARS-CoV-2. The results showed that temperature was the most influential factor compared to RH and UVI for SARS-CoV-2 survival (Chowdhury et al., 2020).
From the above-discussed studies, it can be inferred that the coronavirus in an aqueous environment can survive for a longer period at low temperatures than at higher temperatures, which could be due to the coronavirus respiratory droplets which remain in suspension for a longer time in dry weather. In addition, higher concentrations of organic substances and suspended solids have an impact on the survival of the coronavirus.

Occurrences of SARS-CoV-2 in the aqueous environment and WBE
Most of the known species of viruses inducing SARS-CoV-2 are considered significant human infectious viruses and are often termed enteric viruses that are primarily transmitted via aqueous media, mainly MWW and HWW, through the fecal-oral route (Achak et al., 2021;Ye et al., 2016). These enteric viruses are highly stable infectious agents which can stay on the solids and colloidal particles during wastewater treatment processes and subsequently enter into different water matrices escaping the WWTPs (Randazzo et al., 2020;Serra-Compte et al., 2021). Hence, they may pose severe health risks to humans and aquatic species by causing infectious and deadly diseases and often pose a severe threat to an entire society (Achak et al., 2021;Pietruchinski et al., 2006). The COVID-19 outbreak caused by SARS-CoV-2 in 2019 is one of the most recent examples of the health risk posed by viruses (Achak et al., 2021;D. Zhang et al., 2021).

SARS-CoV-2 RNA concentration in the aqueous environment
With the advancement in analytical techniques and instrumentation, many studies are now available that have reported on the quantification of SARS-CoV-2 RNA in different aqueous media (Kocamemi et al., 2020;Patel et al., 2021). The variation of concentration of SARS-CoV-2 RNA (in copies/L) reported by different countries in the wastewater influent has been represented in Fig. 4(a). The present study reported the SARS-CoV-2 concentration data from 24 countries worldwide between the sampling dates from February 2020 to March 2021. A high concentration of SARS-CoV-2 RNA has been confirmed in countries that reported higher COVID-19 cases during the initial stages of the pandemic, such as South Africa, Brazil, the USA, Mexico, Germany, etc. (Fig. 4(a), Table S3). Zhang et al. (2020) performed one of the first studies on quantifying SARS-CoV-2 RNA in Asian wastewater. The wastewater samples from septic tanks were collected from Wuchang hospital, China, to quantify SARS-CoV-2 RNA using RT-qPCR amplification of two target genes (ORF1 and N protein). The results have shown the occurrence of SARS-CoV-2 RNA with an average concentration ranging from 7.5 × 10 3 to 1.47 × 10 4 copies/L (Table S3). Among the European countries, Saguti et al. (2021) reported one of the first studies to use RT-qPCR to estimate SARS-CoV-2 RNA viral loads in various wastewater matrices. The samples were taken from Rya WWTP in Gothenburg (Sweden) between February and June 2020. The concentration of SARS-CoV-2 RNA in the influent sewage samples ranged between 10 3 to 10 6.27 copies/L (Saguti et al., 2021). Similarly, the first study on the quantification of SARS-CoV-2 RNA from American wastewater was reported by F. Wu et al. (2020). They tested the raw sewage collected from a treatment unit in Massachusetts, USA, using RT-qPCR with a viral load ranging from 5.7 × 10 4 to 3.03 × 10 5 copies/L from 18 to 25 March 2020 (Table S3). Eventually, Johnson et al. (2021) reported one of the first quantitative analyses of SARS-CoV-2 RNA in wastewater among African countries. The untreated sewage samples were collected on June 18, 2020, from four WWTPs in Cape Town, South Africa. The RT-qPCR analysis was used to quantify the viral RNA targeting the N protein gene. All the samples tested positive for SARS-CoV-2 RNA with a viral load ranging between 4.6 × 10 6 -4.54 × 10 8 copies/L (Table S3). Among the countries that have reported the quantitative analysis of SARS-CoV-2 RNA in wastewater, this study confirmed the maximum load of SARS-CoV-2. A possible reason for this could be the high number of active COVID-19 cases reported from the nearby areas of WWTPs (Johnson et al., 2021).
Like wastewater, sewage sludge also hosts many viruses (Gholipour et al., 2022;Prado et al., 2014). Few studies have confirmed the SARS-CoV-2 RNA occurrence in sewage sludge in Turkey, Spain, and the USA (Kocamemi et al., 2020;Peccia et al., 2020). Peccia et al. (2020) tested primary sludge samples collected from WWTPs to quantify SARS-CoV-2 RNA during the COVID-19 outbreak in New Haven, USA, from March 19, 2020, to May 1, 2020. The results indicated a high viral load of 1.7 × 10 6 -4.6 × 10 8 copies/L in the tested samples (Peccia et al., 2020). This suggests that secondary treatment may fail to remove the SARS-CoV-2, which may be due to the adsorption of virus genetic material on suspended particulates during secondary wastewater treatment. Likewise, Kocamemi et al. (2020) and Balboa et al. (2021) have also reported viral load ranging between 1.47 × 10 3 5.03 × 10 3 copies/L and 1.3 × 10 3 2.45 × 10 4 copies/L detected in sludge samples collected from WWTPs of Turkey and Spain, respectively (Table S3). In general, the viral load of SARS-CoV-2 in primary sludge, as reported by a few case studies, was approximately 2-3 times higher than the viral load detected in the wastewater. As a result, sewage sludge can also be considered a significant mode for SARS-CoV-2 transmission (Patel et al., 2021;Peccia et al., 2020).
A few studies have also reported the quantification analysis of SARS-CoV-2 RNA in surface water (Haramoto et al., 2020;Kumar et al., 2022) and groundwater samples (Mahlknecht et al., 2021). For instance, Kumar et al. (2022) and Haramoto et al. (2020) have confirmed the presence of SARS-CoV-2 RNA in the river samples collected in Japan and India, respectively. The viral concentrations in river samples from Japan and India ranged between 2 × 10 2 3 × 10 3 copies/L and 1.37 × 10 2 9.1 × 10 3 copies/L, respectively (Haramoto et al., 2020;Kumar et al., 2022). Likewise, Mahlknecht et al. (2021) performed the RT-qPCR analysis to quantify SARS-CoV-2 RNA in the river and groundwater samples collected in Monterrey, Mexico (America), from December 2020 to January 2021. The results indicated a viral load of SARS-CoV-2 RNA ranging from 2.5 × 10 3 to 7 × 10 3 copies/L and 2.6 × 10 3 to 3.83 × 10 4 copies/L in the river and groundwater samples (Table S3). It can be observed that the viral load detected in groundwater samples was higher than that detected in river samples. This could be due to the infiltration and leaching of surface water and wastewater with positive SARS-CoV-2 RNA from the river beds and faulty sewage conduits, respectively (Mahlknecht et al., 2021).

WBE of SARS-CoV-2 in the aqueous environment
SARS-CoV-2 RNA detection using WBE studies/wastewater surveillance has gained significant attention in identifying and transmitting COVID-19 infections (Huizer et al., 2021;Li et al., 2022;Mandal et al., 2020). Randazzo et al. (2020) tested the influent wastewater samples collected from six WWTPs in areas with a low COVID-19 occurrence in Murcia (Spain). The test results indicated the presence of SARS-CoV-2 RNA in all the influent samples. Moreover, amplified RT-qPCR signals were detected in wastewater when more COVID-19 cases were identified in the city. Also, the wastewater samples tested positive in the Cieza, Lorca, and Totana regions 12-16 days before the actual COVID-19 cases were reported. The study proposed that WBE/sewage surveillance and longitudinal analysis of wastewater can be used as an efficient tool for assessing the presence and prevalence of COVID-19 (Randazzo et al., 2020). Vallejo et al. (2022) established a plot between the natural logarithm of virus concentration detected in wastewater samples from a WWTP (Spain) and the number of active COVID-19 cases using a linear regression model with a regression coefficient of 0.851. The authors considered several parameters, including flow rate, virus concentration, temperature, RH, and rainfall, while designing the model, with the viral load being the most significant among them (Vallejo et al., 2022). Furthermore, a WBE to detect SARS-CoV-2 RNA from two WWTPs in Santiago, Chile, was performed by Ampuero et al. (2020). This study indicated that when the number of COVID-19 patients was low, SARS-CoV-2 RNA was not detected in wastewater. However, when cases increased, the viral load of SARS-CoV-2 RNA also increased gradually, correlating to the number of COVID-19 cases reported from Santiago (Ampuero et al., 2020). Therefore, it is certain that the WBE approach could serve as an alert system for COVID-19 outbreaks before the commencement of COVID-19 disease symptoms in individuals within a community.

Correlation of quantitative load of SARS-CoV-2 RNA with the active COVID-19 cases
In the present review, the authors have attempted to determine a correlation between the average viral load of SARS-CoV-2 RNA detected in the wastewater of different countries with the average active COVID-19 cases reported by the respective country during the sampling period, as shown in Fig. 4(b) and (c). The active COVID-19 data from different countries have been retrieved from various website databases (Coronalevel, 2022;Worldometer, 2022). A manual screening has been performed to extract data on active COVID-19 cases in nearby locations from where the wastewater samples were collected by different studies considered for the present review (Table S4). These active COVID-19 case data were then averaged based on the sampling dates reported in the case studies.
From Fig. 4(c), it can be observed that there is no clear correlation between the concentration of SARS-CoV-2 RNA identified in wastewater from different countries and the average active COVID-19 cases in that country. For instance, in Thessaloniki (Greece), the average viral load of SARS-CoV-2 RNA detected in the influent of WWTP was 2.25 × 10 6 copies/L from 21 April 2020 to 22 June 2020 (Petala et al., 2021). While the average number of active COVID-19 cases in Thessaloniki during the sampling period was only 25 (calculated by dividing the total active COVID-19 cases reported in Greece during the sampling period by the total number of cities) (Coronalevel, 2022;WPC, 2022). Conversely, the study from Louisiana (USA) reported an average concentration of SARS-CoV-2 RNA detected in the influent of a WWTP to be 4967 copies/L from 8 April 2020 to 29 April 2020, while the average active COVID-19 cases in Louisiana during the sampling period was calculated to be 3241 (Sherchan et al., 2020). However, some correlation can be seen among 4 studies from Australia, Portugal, Spain, and South Africa. The studies reported an average concentration of SARS-CoV-2 RNA detected in the influent of a WWTP to be 70 copies/L, 2.98 × 10 5 copies/L, 2.21 × 10 5 copies/L, and 2.29 × 10 8 copies/L, respectively, whereas the average active COVID-19 cases in the study locations were 67, 581, 999, and 4749, respectively during the sampling period (Table S4).
There could be many reasons for the variation in this correlation. Firstly, the sampling stage limitations could be a reason because some studies employed grab sampling techniques while others adopted composite sampling techniques, which might cause variations in viral load concentration at different sites. The second reason could be the inappropriate coronavirus testing in different nations, which may be due to multiple reasons like manual errors while performing tests, instrument errors, or a scarcity of testing kits in some countries. Furthermore, the fact most people with COVID-19 symptoms prefer to self-quarantine rather than have a COVID-19 test could be another reason. Another possible reason for the difference in correlation may be the effects of the normalization of the data. Eventually, human-to-human variation in shedding SARS-CoV-2 RNA via feces and urine could also be a possible cause. Although there is no such clear correlation between the viral loads of SARS-CoV-2 RNA and the active COVID-19 cases among the different countries, the regression graph (Fig. 4(c)) could be utilized as a reference for highlighting a wide range of problems associated with SARS-CoV-2 detection in water matrices. The early warning indicators regarding viral detection by WBE would go a long way towards better managing the outbreak and alerting the respective government authorities to take preventative measures before the situation becomes serious. In addition, various international organizations and regulatory bodies can utilize these data to assess the possible health risk related to wastewater-laden SARS-CoV-2 and later establish disinfection standards for SARS-CoV-2 in different water matrices.

SARS-COV-2 transmission in aqueous environment
Aqueous transmission of coronavirus refers to the possible transmission of the virus from aqueous media to humans via direct or indirect contact with contaminated fluids, including surface water and wastewater, through fecal-oral transmission or via high amounts of open defecation in some parts around the world (Graaf et al., 2017;Teymoorian et al., 2021). The SARS-CoV outbreak (2003) in the apartments of Amoy Gardens, Hong Kong (China), was one of the first and significant examples of coronavirus transmission through sanitary plumbing systems. The empty and dry U-traps in bathroom floor drains used in plumbing systems allowed the virus-laden aerosols to enter the households. A high amount of viral load had accumulated in the sanitary system. Subsequently, the virus-laden aerosols were inhaled, ingested, or transmitted via fomites, leading to an outbreak of SARS in the entire building (Gormley et al., 2017;Haji Ali et al., 2021). As discussed, SARS-CoV and SARS-CoV-2 RNA have nearly identical stability on aerosols and various surfaces. Hence, feces and urine could be plausible pathways for SARS-CoV-2 transmission via aqueous media, as depicted in Fig. 5.
Recently, studies have reported the presence of SARS-CoV-2 in stool samples taken from infected individuals (including asymptomatic patients) from COVID-19 ward hospitals worldwide (Liu et al., 2021;. Ong et al. (2020) investigated stool samples of patients from a COVID-19 hospital ward in Singapore. The study found that about 60% of the samples collected from the wash basin, toilet seats, and door handle tested SARS-CoV-2 positive (Ong et al., 2020). Likewise, Tang et al. (2020) tested the fecal specimen of an asymptomatic child who was later confirmed COVID-19 positive with SARS-CoV-2 RNA detected in the stool sample, even though the respiratory tract specimens were SARS-CoV-2 negative (Tang et al., 2020). Furthermore, W.  also reported live SARS-CoV-2 RNA in the fecal specimen of two patients with no diarrhea in a hospital in Beijing (China) (W. . SARS-CoV-2 RNA shedding via urine and feces by infected individuals may discharge into the sewers and then can enter into sewage systems (Medema et al., 2020;F. Wu et al., 2020). Eventually, these sewage systems may be considered one of the significant routes of SARS-CoV-2 transmission in the aqueous environment (Barcelo, 2020;Giacobbo et al., 2021). Based on the above studies, it can be inferred that SARS-CoV-2 RNA could be more persistent in the  Further, the high viral load of SARS-CoV-2 might cause direct and indirect effects on the aqueous environment. For instance, the direct effects are mostly related to the various viral disinfection methods used in multiple stages of treatment in WWTPs, which may raise the overall cost of treatment. At the same time, the indirect impacts are mostly related to the overuse of cleaning and disinfecting products to protect against viral transmission and the overconsumption of certain pharmaceutical drugs to protect against viral symptoms. This unexpected situation causes changes in water and wastewater quality and may possess adverse and harmful consequences for humans, aquatic organisms, and the environment (Teymoorian et al., 2021).

Treatment technologies for the inactivation of SARS-CoV-2
Tracking and evaluating SARS-CoV-2 removal from WWTPs using existing and advanced technologies are essential because the survival of SARS-CoV-2 in a contaminated aqueous environment can be a significant mode of transmission of COVID-19 (Patel et al., 2021;Tran et al., 2021). Several studies have reported that the existing and advanced treatment technologies, such as chlorine disinfection, heat treatment, and advanced oxidation processes (AOPs), have been successfully applied to inactivate enveloped viruses, including coronaviruses (Kataki et al., 2021;Tran et al., 2021). According to the USEPA report, disinfectants such as ethanol, hypochlorites, hydrogen peroxide, mono persulfates, quaternary ammonium salts, chlorine dioxide, etc., can be utilized for the inactivation of SARS-CoV-2 RNA from an aqueous environment (USEPA, 2021).

Performance of secondary treatment on SARS-CoV-2 removal
Recently, many studies have investigated the removal of SARS-CoV-2 from sewage systems (Greaves et al., 2022;Rimoldi et al., 2020). Among these studies, few confirmed that SARS-CoV-2 was still there after secondary treatment in WWTPs, indicating secondary treatment cannot completely inactivate the virus from wastewater (Randazzo et al., 2020;Serra-Compte et al., 2021). For instance, Randazzo et al. (2020) revealed the existence of SARS-CoV-2 in the secondary treated wastewater. Coagulation and flocculation, followed by sand filtration, ASP, and extended aeration, were employed as secondary treatment units. The study reported about 11% (i.e., 2 out of 18) samples tested SARS-CoV-2 positive after secondary treatment, whereas all tertiary treated wastewater samples tested negative (Randazzo et al., 2020). SARS-CoV-2 may adsorb on the surface of suspended solids and colloidal particles due to the fragile lipid membrane enveloping the virus protein capsid. This could be one possible reason for their poor removal during secondary wastewater treatment (Randazzo et al., 2020;Serra-Compte et al., 2021).
In contrast, a few studies also confirmed the absence of SARS-CoV-2 RNA in secondary treated effluents despite positive results in the influent samples. Kumar et al. (2020) evaluated the results of secondary treated sewage samples collected from a WWTP in Ahmedabad (India). The WWTP was a small capacity plant with a maximum flow of 180 m 3 /day with an aeration pond and up-flow anaerobic sludge blanket applied as secondary treatment units. The maximum influent viral concentration was observed to be 350 copies/L. According to the findings, SARS-CoV-2 RNA was absent in the treated sewage effluent samples (Kumar et al., 2020). Similarly, Sherchan et al. (2020) also confirmed no occurrence of SARS-CoV-2 in the secondary treated effluent samples collected from a WWTP in the USA when a maximum virus influent concentration was close to 7500 copies/L (Sherchan et al., 2020). The low influent viral concentration and the nature of the secondary treatment applied could be possible reasons for the absence of SARS-CoV-2 strains in the secondary treated effluent samples in these studies. According to the findings of the studies mentioned above, it could be suggested that while conventional treatment plants can remove SARS-CoV-2, a tertiary treatment (e.g., disinfection) of wastewater is recommended for the complete inactivation of any virus strains.
A few studies have focused on applying secondary treated effluents without any tertiary treatment for irrigation and gardening purposes, which may pose public health risks if the water is still contaminated with SARS-CoV-2 (Haji Ali et al., 2021;Randazzo et al., 2020). Therefore, validating the SARS-CoV-2 presence in treated and untreated wastewater becomes critical, as these wastewaters can be a significant source of viral transmission in the community.

Tertiary treatment and advanced disinfection techniques for inactivation of SARS-CoV-2
Tertiary treatment techniques, such as chlorine and hydrogen peroxide disinfection, ozonation, UV irradiation, heat radiation, etc., have been successfully employed for wastewater treatment (Huang et al., 2011;Zahmatkesh et al., 2022). Some of these techniques have been investigated for the removal of SARS-CoV-2 from different water and wastewater samples, as represented in Fig. 6. Furthermore, chlorination, ozonation, and UV irradiation are the most sought methods for HWW disinfection (Kovalova et al., 2013;Zhang et al., 2020). Disinfection of wastewater with chlorine is one of the most preferred methods due to its low cost and powerful oxidizing properties (J. Zahmatkesh et al., 2022). Some chlorine-based disinfectants like sodium hypochlorite, chlorine dioxide, and liquid chlorine have been used in recent studies to inactivate SARS-CoV-2 from wastewater (Zahmatkesh et al., 2022;D. Zhang et al., 2021). The chlorine-based disinfectants destroy the outer cell membrane of viruses by breaking the chemical bonds in their molecules (Virto et al., 2005). Coronaviruses are extremely delicate to chlorine-based disinfectants and become unstable when exposed to free chlorine (Patel et al., 2021;Tran et al., 2021).
Recently, Serra-Compte et al. (2021) assessed the efficacy of chlorination for SARS-CoV-2 inactivation in sewage samples collected from a Spanish WWTP. No traces of SARS-CoV-2 were detected after employing MBR, followed by chlorination, suggesting chlorine is a powerful disinfectant for SARS-CoV-2 inactivation (Serra-Compte et al., 2021). Similarly, Greaves et al. (2022) investigated the performance of chlorine disinfection using sodium hypochlorite on MWW and deionized (DI) water samples spiked with SARS-CoV-2 RNA. The results indicated a chlorine dose of 10 mg/L with a contact time of 30 min and 1 min for wastewater and DI water samples, respectively, was sufficient for achieving 100% inactivation of SARS-CoV-2 RNA (Table S5). It can also observe that the SARS-CoV-2 was inactivated rapidly in DI water samples compared to wastewater samples. This was expected as the wastewater contains a high load of organic matter and other pathogens that may consume some of this disinfectant. Eventually, the study suggested free chlorine disinfection can be a vital option for reducing SARS-CoV-2 in water and wastewater (Greaves et al., 2022).
In addition, Zhang et al. (2020) tested the performance of chlorine disinfection (using an 800 g/m 3 dosage of sodium hypochlorite with a contact period of 1.5 h) for SARS-CoV-2 inactivation from untreated and treated sewage samples collected from a septic tank of a hospital in Wuchang, China (Table S5). It was observed that free chlorine was not detectable after 12 h of adding sodium hypochlorite, but the SARS-CoV-2 was still detected in the effluent, which was explained due to the protection provided by the suspended solids and organic substances by adsorbing SARS-CoV-2 onto their surfaces. It can be concluded that a free chlorine concentration of 6.5 mg/L cannot secure complete disinfection of SARS-CoV-2. Eventually, increasing the sodium hypochlorite dosage to 6700 g/m 3 with a free chlorine concentration of 21-25 mg/L resulted in negative SARS-CoV-2 RNA in the effluent. However, disinfection by-products in the form of trichloromethane, tribromomethane, bromodichloromethane, and dibromochloromethane were detected in the effluent . Based on the above studies, it could be suggested that, although chlorine disinfection can V.K. Parida et al. completely inactivate the SARS-CoV-2 in wastewater, it should be utilized in a controlled manner. Overdosing chlorine can result in carcinogenic disinfection by-products, which can pose severe risks to public health (Fig. 6).
UV irradiation is another commonly used disinfection method for water and wastewater. A wavelength ranging from 200 to 400 nm can damage the RNA and DNA structures of viruses, the cell membrane of bacteria, and other single-celled microorganisms (Patel et al., 2021;Zahmatkesh et al., 2022). Compared to chlorine disinfection, UV disinfection has shown better virus inactivation results and low health effects (APEC, 2022). Rimoldi et al. (2020) evaluated the performance of UV irradiation for the inactivation of SARS-CoV-2 from the wastewater samples collected from three WWTPs located in Milano (Italy). All the plants were equipped with secondary treatment followed by a tertiary disinfection step using high-intensity UV lamps. All three tested SARS-CoV-2 genes (ORF1ab, N, E) were negative in the effluent wastewater samples, indicating complete inactivation of the virus in the treated wastewater (Table S5). However, disinfection with UV has certain drawbacks, such as higher operation and maintenance costs and lower residual power (Kataki et al., 2021). Therefore, large-scale application of UV disinfection is still a significant challenge for water and wastewater treatment, despite satisfactory results obtained by UV disinfection (Fig. 6).
Only a few studies have been conducted on the inactivation of SARS-CoV-2 from stock virus titers and real wastewater samples using heat irradiation. Bivins et al. (2020) studied the inactivation behavior of SARS-CoV-2 at different temperatures using the Eppendorf heat block. The experiment was performed by inoculating SARS-CoV-2 (nCoV-WA1-2020) viral stocks into two 15 mL sewage samples collected to form a municipal WWTP in Indiana (USA). It was observed that at room temperature, 99% of the SARS-CoV-2 was inactivated (T 99 ) in 3-5 days, whereas at 50 • C, T 99 was achieved in 15 min, and when the temperature was further increased to 70 • C, T 99 was achieved only in 4.5 min (Bivins et al., 2020). Likewise, Burton et al. (2021) and T.  also investigated the performance of heat radiation for SARS-CoV-2 inactivation from stock virus titers. When the temperature was increased to 60 • C and 95 • C, the SARS-CoV-2 RNA was inactivated entirely for 15 min and 1 min, respectively (Table S5). Based on the above studies, it can be inferred that thermal treatment can completely inactivate SARS-CoV-2. However, large-scale wastewater treatment using heat irradiation is still a significant challenge. Further, some heat-resistant particles may remain in the inactivated samples, posing post-treatment health risks (Scheller et al., 2020). Some of the AOPs have been studied for the inactivation of SARS-CoV-2 titers from stock samples. For instance, Matsuura et al. (2021) reported a 99.9% inactivation of SARS-CoV-2 from aerosol samples using TiO 2 photocatalyst immobilized on a glass sheet with a contact time of 120 min (Table S5) Table S5].
V.K. Parida et al. performance of ozonation on SARS-CoV-2 inactivation. It was found that a 99% reduction of virus RNA was achieved with an ozone dosage of 0.2-0.8 mg/L within 1 min (Martins et al., 2021).
Although there is no indication of SARS-CoV-2 presence in the tertiary treated wastewater using chlorine disinfection, disinfection byproducts have been reported by a few studies due to an overdose of these disinfectants. Therefore, further research is required to determine the optimal disinfectant dosage to minimize any potential health risks caused by them. The current review explores various disinfection techniques that have been/are being used for the disinfection of SARS-CoV-2 from wastewater.

Impact of COVID-19 on the general public and water environment
The COVID-19 pandemic has caused immense loss of human life worldwide by affecting routine life, public health, food security, and businesses by interrupting global trade and movements (Chriscaden, 2020;Haleem et al., 2020). Apart from social and economic impacts, the COVID-19 outbreak had an impact on the healthcare sector, such as challenges in diagnosing and treating suspected or confirmed cases, overcrowding of patients and shortage of doctors in hospitals, scarcity of medical equipment such as ventilators, oxygen cylinders, etc. (Haleem et al., 2020;Rajit et al., 2020). The bulk production of single-use medical items, including masks, gloves, PPE kits, etc., has elevated the quantity of solid waste generated worldwide (Islam et al., 2021).
The emergence of COVID-19 in the past two years has also influenced water and wastewater qualitatively and quantitively. Many studies have reported increased daily water consumption during the lockdown due to repetitive hand washing and cleaning of clothes, utensils, fruits, vegetables, house cleaning, etc. (Balamurugan et al., 2021;Donde et al., 2021). Furthermore, few studies have reported the excessive use of soaps and hand sanitizers has deteriorated the quality of the wastewater generated (Donde et al., 2021;Gwenzi et al., 2022). Moreover, this situation worsened in lower-middle-income countries lacking full-fledged working WWTPs, severely affecting the environment. Due to the rise in water consumption in many countries during the lockdown period, there is a strong possibility of an increase in wastewater generation (Donde et al., 2021;Kataki et al., 2021). During the lockdown period, people worldwide were practicing self-medication, resulting in increased consumption of medicines. Further high concentrations of pharmaceutically active compounds and other drug residues were released into the wastewater (Bandala et al., 2021;Kamilya et al., 2023). These compounds have a complex structure and are hydrophilic; thus, they are partially degraded during the secondary treatment process and are thus introduced into the surface water, causing a severe threat to the aquatic environment and human health (Parida et al., 2021;Patel et al., 2019).

Measures were taken for effective wastewater management
To overcome the global loss and to combat the ongoing COVID-19 pandemic spread, various international organizations such as WHO, USEPA, etc., and national government authorities across the world have recommended interim guidance and protocols on infection prevention and control strategies (Donde et al., 2021;USEPA, 2022;WHO, 2022). For instance, the WHO has developed a comprehensive technical guidance report for managing COVID-19 patients (WHO, 2022). Likewise, Pan American Health Organization has given general recommendations for all healthcare facilities worldwide to discharge their wastewater to a sewer system connected to treatment plants or, in the absence of WWTPs, to a septic tank or oxidation pond during the pandemic period. They also recommended using masks, gloves, PPE kits, and face shields for the sewage and sanitation operators while handling HWW and biomedical waste generated from hospitals with COVID-19 patients admitted (PAHO, 2020). Similarly, in India, Central Pollution Control Board has also issued guidelines to ensure the safety of WWTP operators recommending the use of appropriate PPE kits, face masks, waterproof coveralls, safety shoes, etc. The guideline also recommends not reusing treated wastewater for agriculture (CPCB, 2020). The USEPA also suggests a few precautionary measures and standard operating protocols for WWTP workers and operators avoid direct exposure to wastewater. Precautions such as applying administrative and engineering controls and a safe work environment must be practiced to control COVID-19 transmission (USEPA, 2022).
During the initial stage of the pandemic, most countries were proactive in taking preventive actions in the form of complete lockdowns to curb the spread of SARS-CoV-2 (Auger et al., 2020;Haque et al., 2021). Because of the implementation of these efforts in the majority of countries, the spread of COVID-19 was relatively controlled. In the later stages of the pandemic, when the count of new cases of COVID-19 increased daily, most countries turned to digital assistance in the form of mobile phone applications for controlling the transmission of COVID-19 (Lee and Kim, 2021;Murray et al., 2020). These applications generally contact tracing-based application software that uses the global positioning system (GPS) technology to provide information on the number of COVID-19 cases updates, tracing the movement of individuals and those with whom they come into contact, the risk of acquiring COVID-19, as well as identifying COVID-19 symptoms (Lee and Kim, 2021;Murray et al., 2020). Among Asian countries, China, Hong Kong, and Taiwan have launched several apps that enable direct geolocalisation via cell phone networks to identify more suspected areas of COVID-19 . Similarly, the Indian government has launched the Aarogya Setu ("Bridge to Health") application for contact tracing. There has been a decline in the new COVID-19 cases in India due to the efficient use of the application (NIC, 2020). The Gulf countries, including UAE, Qatar, and Bahrain, have adopted Bluetooth-based contact tracing applications that use a more privacy-preserving design to register close contacts (Presse, 2020;Shahroz et al., 2021). Due to privacy concerns, Canada, Mexico, and most European countries have adopted a few privately developed contact tracing applications (Presse, 2020). Most governments are enforcing the digital-based platform to prevent new outbreaks of COVID-19 infections which would overwhelm healthcare centers already dealing with the outbreak (Presse, 2020).

Application of computational modeling methods
Along with government officials and policymakers, researchers, programmers, software engineers, and developers worldwide are also working hard to find ways of controlling COVID-19 transmission. During this pandemic period, the use of computational-modeling methods, including fuzzy logic, blockchain, system dynamics, etc., has also played a crucial role in the efficient management of COVID-19 and has provided possible ways to aid government authorities in the effective management of the pandemic (Aggarwal et al., 2021;Choudhury et al., 2021). A few of these methods are explained in the following sections. Fig. 7 represents various computational models along with their attributes and application in the context of COVID-19.

Blockchain
A Blockchain is a decentralized and distributed book for performing peer-to-peer (P2P) networking. Blockchain has gained popularity due to its features, such as absoluteness, transparency, and decentralization, since its development (Gupta and Kumar, 2018). In the ongoing COVID-19 pandemic, researchers have implemented blockchain technology to tackle the outbreak effectively (Fig. 7). Torky and Hassanien (2020) proposed an innovative approach using blockchain technology to detect the unknown infected person using a pattern recognition system. The details of this system have been discussed briefly in section 1.3 of V.K. Parida et al. the supplementary table. Recently, MiPasa, a blockchain-based data platform developed by HACERA company in collaboration with WHO and other technology firms for sharing and using data about the COVID-19 pandemic from multiple providers which can be accessible to the general public, researchers, decision-makers, government officials, etc., across the world (Rakhmilevich, 2020).

System dynamics
Most individuals with COVID-19 symptoms do not enroll for contact tracing, resulting in many false COVID-19 reported cases (Lewis, 2020). Hence, there could be an unusual level of uncertainty and variability in COVID-19 cases reported by countries. Therefore, systems dynamics offer a broad approach to understanding these uncertainties in the systems (Jia et al., 2022). These systems can be used to optimize policies and plans for decision-making during a pandemic (Fig. 7) (Fair et al., 2021;Jia et al., 2022). Fair et al. (2021) have investigated the uncertainties in testing and optimized strategies for detecting and identifying COVID-19-infected patients using a system dynamics epidemiology model with parameters such as hospitals, masks, contact tracing, social distancing, and testing tools. The findings show rigorous testing, contact tracing, and lockdown can help to prevent an outbreak by identifying asymptomatic individuals in the population (Fair et al., 2021).

Fuzzy logic
When an arithmetical solver is insufficient to achieve reliable data, fuzzy logic, an AI-based system, is commonly used for problem-solving. To deal with extreme situations, it employs a soft computing system. The system improves known entities by converting them to arithmetic and functional parameters in surface graphs Chowdhury et al., 2020). Recently, a few researchers have used fuzzy logic to evaluate the effectiveness of different environmental conditions during the ongoing COVID-19 pandemic (Fig. 7). For instance, Chowdhury et al. (2020) took the temperature, RH, and UVI data of a few COVID-19 infected countries and used them as input parameters, and the number of infected individuals was used as output variables, to obtain a correlation between them. The plotted surface graph revealed temperature and RH have a more significant impact on the number of infected individuals than UVI (Chowdhury et al., 2020).

Artificial neural network
An artificial neural network (ANN) can model complex systems (Park and Lek, 2016). Recently, researchers utilized neural networks in combination with genetic algorithms to model and estimated the number of infected/death cases without the assumptions required for epidemiological models (Shawaqfah and Almomani, 2021). The ANN model can be used to predict the long-term spread of the pandemic by taking short-term data inputs. The ANN can be considered as an alternative to the WBE models for showing accurate prediction of COVID-19 outbreaks among communities (Fig. 7). For instance, Shawaqfah and Almomani (2021) developed an ANN algorithm for forecasting the COVID-19 infection/death cases in three countries, namely Spain, Italy, and Qatar. The obtained forecasted COVID-19 values (infected/death cases) were close to the real reported cases on specific dates with a high regression coefficient (≥ 0.99). The algorithm can be adaptable by different countries for forecasting COVID-19 based on population density, climate conditions, and other social circumstances (Shawaqfah and Almomani, 2021).

Machine learning
Machine learning (ML) is a kind of AI that enables software applications to produce increasingly accurate results for predicting events without being specifically designed to provide it (TechTarget, 2022). The features like faster processing power and highly reliable and accurate results compared to manual data processing have enhanced the application of ML in a wide range of healthcare tasks management, including the management of the COVID-19 pandemic (Fig. 7). Sun et al. (2020) developed a support vector machine model based on ML algorithms to predict COVID-19 patients who might proceed to severe/critical symptoms, allowing healthcare resources to be used more efficiently. The model optimized the combination of parameters such as age, glutathione, cluster of differentiation 3, and total protein to V.K. Parida et al. generate accurate results in discriminating between mild and severe/critical cases .

Big data
Big data is a set of techniques created to store, analyze and manage bulk data and methodically extract information from it or handle huge/ complicated data volumes that are difficult for conventional dataprocessing application software to handle (SAS, 2022). During the ongoing pandemic, a vast and varied amount of data has been generated, increasing daily. Moreover, this data could be utilized in various ways, such as diagnostics, predicting and estimating risk scores, and healthcare decision-making by employing effective data analytics approaches (Fig. 7) (Alsunaidi et al., 2021;J. Wu et al., 2020). In the case of diagnosis, the big data tool could be implemented to detect pre-symptomatic COVID-19 patients, detect actual COVID-19 cases, and monitor COVID-19 discharged patients. When it comes to assessing the risk of the COVID-19 outbreak, big data can be useful for identifying COVID-19 hotspots, contact tracing, etc. (Alsunaidi et al., 2021).

Summary of findings and future aspects
In the present review, the authors have discussed the occurrence, detection analysis, persistence, mode of transmission, and potential management of SARS-CoV-2 in the aqueous environment. During the ongoing pandemic, this review could benefit both the professionals (researchers, policymakers, government officials, environmental engineers, etc.) and the general public. The findings could assist them in understanding the various modes of SARS-CoV-2 transmission, its persistence on multiple surfaces, types of detection methods, and different disinfection strategies used to successfully manage SARS-CoV-2 in the environment, particularly wastewater and sewage sludge. The paper also highlights the application of WBE/sewage surveillance in many countries for early detection and transmission of SARS-CoV-2 infection before the actual COVID-19 cases are reported from these locations. Furthermore, the efficiency of disinfection techniques such as chlorination, ozonation, and UV irradiation for SARS-CoV-2 inactivation from real wastewater has been reviewed. The authors also addressed the measures taken by international organizations and government authorities worldwide to effectively manage the COVID-19 outbreak, including the application of computational modeling methods.
However, there are still many research gaps in the existing literature which are needed to be addressed at the earliest to decelerate the spread of COVID-19 infection among the countries. To overcome these research gaps, a few recommendations have been suggested: (1) statistical analysis and transmission modeling are needed to be carried out to determine whether different water matrices can be a possible route for SARS-CoV-2 transmission in a community. (2) Risk assessment studies should be conducted in nearby locations of wastewater treatment facilities to assess the risk of COVID-19 in those locations. (3) More research is needed to be conducted regarding the persistence of SARS-CoV-2 in different water matrices, as influencing factors such as temperature, RH, pH, organic solids, etc. play a significant role in its survivability. The application of computational models could optimize different parameters so that the spread of COVID-19 infections can be controlled with minimum resources. (4) Although WBE studies are adequate for early detection of the spread of COVID-19 globally, no proper WBE systems have been developed at regional levels. The national and regional level healthcare organizations must introduce wastewater-based surveillance for monitoring and alerting the locals about the rise in COVID-19 cases in possible hotspots. (5) Although most studies have reported almost complete inactivation of the SARS-CoV-2 from wastewater by employing tertiary treatment (disinfection), a few of them have reported the carcinogenic disinfection by-products to remain in the water for a more extended period due to the overdose of disinfectants. As a result, they may pose a severe threat to the aquatic environment and humans. To address this issue, relevant protocols and regulatory guidelines for the disinfection of SARS-CoV-2 from water and wastewater must be established by the relevant scientific communities and government authorities.

Declaration of competing interest
The authors 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
No data was used for the research described in the article.