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Coronavirus And The Water Cycle — Here Is What Treatment Professionals Need To Know

By Nicole McLellan, David Pernitsky, and Arthur Umble

coronavirus (002)The spikes on the surface of coronaviruses give this virus family its name — corona, which is Latin for “crown.”

As the global health community tracks the spread of this virus, it’s important for water and wastewater professionals to keep updated on potential impacts.

It's hard to miss the headlines. The recent outbreak of novel coronavirus (2019-nCoV or COVID-19) has dominated news cycles in recent weeks. The World Health Organization (WHO) is calling it “public enemy number one.” But what information do we have that is related to coronaviruses in water and wastewater systems? And what can water- and wastewater-system operators do to protect public health?

Modern water and wastewater treatment systems play an important role in public health protection. With the potential for environmental transmission, water and wastewater operators need to know the potential for survival of this type of virus in water and wastewater treatment systems.

Coronaviruses, named for the crown-like spikes on their surface, were first identified in the mid-1960s. Currently, seven coronaviruses are known to infect people and make them ill. Three of these — MERS-CoV, SARS-CoV, and COVID-19 — emerged in the last 20 years and are examples of how some coronaviruses that infect animals can evolve to infect humans. COVID-19 is a new variety of coronavirus and is an enveloped, single-stranded (positive-sense) RNA virus.

So, what is the fate of coronavirus in sewage and wastewater treatment plants? Or in the aquatic environment? And should we be worried about the efficacy of water treatment filtration and disinfection processes for coronavirus removal and inactivation?

The short answer: No — if we take proper precautions and risk considerations.

The long answer: This is a new virus without an extensive body of literature on the effectiveness of water and wastewater treatment processes. And real-life experiences will vary due to water quality and treatment plant details.

According to a 2008 University of Arizona study, coronaviruses have not been found to be more resistant to water treatment than other microorganisms such as E. coli, phage, or poliovirus — which are commonly used as surrogates for treatment performance evaluations. Results from bench-scale studies suggest that the survival of coronaviruses is temperature dependent, with greater survival at lower temperatures. Therefore, coronavirus is expected to be reduced in raw wastewater and surface waters in warmer seasons. 

How is it transmitted?

Human viruses do not replicate in the environment. For a coronavirus to be transferred via the water cycle, it must have the ability to survive in human waste, retain its infectivity, and come in contact with another person — most likely via aerosols. Findings suggest that COVID-19 can be transmitted through human waste.

Should a major virus pandemic occur, wastewater and drinking water treatment industries would face increased scrutiny. Utilities would need to respond rapidly to minimize occupational and public health risks based on the available evidence. Wastewater effluents would possibly impact recreation, irrigation, and drinking waters. While wastewater treatment does reduce virus levels, infective human viruses are often detected in wastewater treatment plant effluent.

Information for wastewater treatment plant operators

Typically, human waste entering a sewage system is carried through an underground pipe system to a municipal treatment plant. Wastewater treatment plants receiving sewage from hospitals and isolation centers treating coronavirus patients — and domestic sewage from areas of known large contamination — may have elevated concentrations of viruses. Wastewater is treated by a variety of processes to reduce the pollution impacts on nearby receiving waters (lakes, rivers) and disinfected.

Currently, major data gaps exist on the potential role of the water cycle in the spread of enveloped viruses. The lack of detection methods for these strains of viruses is a main reason this type of information is still relatively unknown. Most detection methods are designed and optimized for non-enveloped enteric viruses, and there just isn’t enough information available.

In general, secondary wastewater treatment is credited with removing 1-log (90 percent) of viruses, though broad studies suggest the level of virus removal is highly variable, ranging from insignificant to greater than 2-log removal (99 percent). Because of this variability, the primary process for the inactivation of viruses in wastewater treatment is chemical disinfection (e.g., chlorination) and/or by ultraviolet light.

Drinking water treatment is an effective barrier

Surface-water treatment plants with upstream wastewater impacts are the most susceptible to having coronavirus contamination in the raw water supply during, and after, an outbreak. Viruses are exposed to several potentially inactivating stresses in surface waters, including sunlight, oxidative chemicals, and predation by microorganisms. Generally, enveloped viruses are more susceptible to common drinking water disinfectants than non-enveloped viruses.

Based on published research, water treatment processes that meet virus removal/inactivation regulations are effective for coronavirus control.

For example, drinking water quality guidelines from Health Canada note conventional treatment with free available chlorine can achieve at least 8-log inactivation of viruses in general. Of course, disinfection performance must be continuously monitored (e.g., turbidity, disinfectant dose, residual, pH, temperature, and flow). Optimized conventional filtration can achieve 2-log (99 percent) virus removal and is just one of many processes water treatment facilities incorporate to make our water safe to drink.

Modern drinking water treatment plants are well equipped to remove and disinfect viruses through filtration and disinfection processes.

So now what?

By and large, these viruses are not considered a major threat for the wastewater and water industries due to their low concentrations in municipal wastewater and high susceptibilities to degradation in aqueous environments. According to new OHSA guidance, there is no evidence to suggest that additional, COVID-19-specific protections are needed for employees involved in wastewater treatment operations.

The WHO found that risk communication and community engagement (RCCE) has been integral to the success of response to health emergencies. Action items related to coronavirus include communicating about preparedness measures and establishing a system for listening to public perceptions to prevent misinformation.

Basic recommendations for treatment-plant operators when dealing with a potential virus outbreak

So far, this virus does not appear to survive well in the environment and can be eliminated effectively by water treatment, especially chlorination, and would pose a minimal risk through drinking water. As the outbreak continues, more water-quality experiments are needed before major conclusions can be drawn on their fate within treatment processes. While this will be tricky, especially as viruses continue to replicate and evolve, quantitative risk assessments should be a top priority for enveloped viruses in wastewater, recreational waters, and drinking water.

Treatment-plant operators can download this white paper for more details on current state of knowledge on coronaviruses as it relates to our practice. For additional reputable and reliable sources of information that are updated frequently with technical guidance, public health information, and the latest research visit the Water Environment Federation’s coronavirus site

About the authors

Nicole McLellan is an environmental scientist. She has an academic background in environmental microbiology and civil engineering for drinking water treatment performance evaluations.

David Pernitsky is global practice leader for water treatment. He has more than 25 years of environmental engineering experience, managing many challenging studies.

Arthur Umble is Stantec’s global lead for wastewater practice. He develops strategies and provides solutions for complex wastewater treatment challenges.


Michael Schmitt· 

I just read this: It has been established with other human pathogens that formation of droplets and aerosols from water contaminated with microorganisms can serve as a vehicle for transmission. Examples include Legionella, a respiratory pathogen acquired when contaminated water droplets are inhaled (Butler and Breiman, 1998), and Cryptosporidium, an enteric pathogen acquired via ingestion of contaminated droplets (CDC, 1998). Desiccation and aerosolization of body fluids and fecal matter, resulting in ingestion or inhalation of dried particles, can also serve as a source of pathogens such as norovirus (Marks et al., 2003) and hantavirus (LeDuc, 1998). SARS was spread when water contaminated with fecally shed virus was inhaled, causing respiratory infection. This person-to-person fecal droplet–respiratory transmission route was observed in the Amoy Gardens apartment building outbreak in Hong Kong, the largest point-source outbreak attributable to this type of transmission pathway. When an individual shedding infectious virus in feces used the toilet facilities in a building, a combination of faulty drain traps and powerful exhaust fans in residential units resulted in virus-laden liquid droplets being drawn from the waste system into living spaces via floor drains. The droplets were inhaled by occupants and carried on air currents to other areas of the building, resulting in a large number of SARS cases (WHO, 2003, McKinney et al., 2006). More data are needed on the survival of SARS-CoV in fecal droplets and aerosols to assess this new risk pathway in the event that SARS reemerges. The results of this study suggest that coronaviruses can survive long enough in water and sewage for these vehicles to serve as a source of exposure. The potential for long-term survival, along with the airborne fecal droplet transmission model, suggests that fecally contaminated aqueous media could pose a health risk in future outbreaks.

If water or sewage contaminated with SARS-CoV becomes aerosolized, it could potentially expose large numbers of people to infection. This could create an ongoing risk during an outbreak, even with quarantine measures to isolate infected individuals. Commercial, residential, and hospital water or sewer systems contaminated with persistent infectious SARS-CoV might defeat quarantine measures by continuing to spread virus even after infected individuals have been removed from the area. The persistence of coronaviruses in water and sewage in this study suggests that quarantine measures, which proved effective in containing the last SARS outbreak, could be seriously undermined unless adequate attention is paid to the safety and security of building plumbing systems. For assessment of these risks, further work is necessary to better define the kinetics of SARS-CoV survival and inactivation in water, sewage, and other aqueous media. The survival and persistence data presented here show that TGEV and MHV may serve as conservative indicators of the survival of SARS-CoV in water and sewage, providing a starting point for risk assessments of water and sewage as vehicles for SARS transmission.

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5. Conclusions
• The coronaviruses TGEV and MHV survived and remained infectious for long periods in different water types, including reagent-grade water, surface water, and pasteurized settled sewage.
• Both viruses survived and remained infectious at both low (4 °C) and ambient (25 °C) temperatures.
• In all water types tested (reagent-grade water, lake water and settled sewage), the titer of infectious virus declined more rapidly at 25 °C than at 4 °C.
• Water type, incubation time, and temperature were significant predictors of log10 viral reduction kinetics.
• The persistence of coronaviruses in water observed in this study suggests that if SARS-CoV should reemerge in human populations, water contaminated with these viruses may continue to pose an exposure risk even after infected individuals are no longer present.

About the author

Dr. Howard Dryden

Dr. Howard Dryden

Dr. Dryden has unique knowledge combination of biology, chemistry and technology and is the inventor of the activated, bio-resistant filter media AFM®. Dr. Dryden is one of the world`s leading experts in sustainable water treatment.

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