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
By Nicole McLellan, David Pernitsky, and Arthur Umble
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, it is important to know the potential for transmittance of this type of virus in water and wastewater treatment systems, especially for water and wastewater operators.
The spikes on the surface of coronaviruses give this virus family its name—corona, which is Latin for “crown.”
Coronaviruses, named for the crown-like spikes on their surface, were first identified in the mid-1960s. Currently, seven coronaviruses are known to infect humans 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 an enveloped, single-stranded (positive-sense) RNA virus and is a new variety of coronavirus.
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 persistence of coronaviruses is temperature dependent, with greater persistence at lower temperatures (i.e. 5oC). 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 persist in human waste, retain its infectivity, and come in contact with another person’s eyes nose or mouth —most likely via aerosols or droplets. Findings suggest that COVID-19 can be transmitted through human waste.
_q_tweetable:Modern drinking water treatment plants are well equipped to remove and inactivate viruses through filtration and disinfection processes._q_With a pandemic, wastewater and drinking water treatment industries face increased scrutiny. Utilities need to respond rapidly to minimize occupational and public health risks based on the available evidence. Wastewater effluents could impact recreation, irrigation, and drinking waters. While wastewater treatment does reduce virus levels, infective human viruses have been 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 population infection—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 monitoring for these strains of viruses is a main reason this type of information is still relatively unknown. Common methods used for the detection of human viruses in water supplies are riddled with technical issues which are mostly due to the fact that human viruses are often in low concentrations in the environment and the filtration of large quantities of water to isolate these viruses for their detection is not feasible.
The genetic material of COVID-19 has been detected in raw wastewater, and COVID-19 is capable of binding to cells in the human gut. Further, in at least one study, COVID-19 has been detected in the stool of an infected person using electron microscopy and a culture method which indicates that this virus can be excreted in an infectious state. Collectively, this information indicates that infectious COVID-19 may be present in raw wastewater. Therefore, wastewater operators who are doing work that is deemed essential or critical near raw wastewater or where droplets may be produced should introduce protections assuming there is a risk of transmission. These barriers may include:
- Sufficient PPE to cover the eyes, nose, and mouth (e.g., a face shield)
- Social distancing of at least 2 m (6 ft) from other personnel
- Frequent handwashing
- Routine washing or disinfecting of commonly touched surfaces, footwear, and laundering of clothing
- Replace in-person, shift-change meetings with virtual meetings
- Exploring what solutions technology can provide for remote monitoring and operation
In general, secondary wastewater treatment can remove about 1-log (90%) 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 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%) 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 inactivate viruses through filtration and disinfection processes.
So now what?
By and large, these viruses are not considered a major threat for the water industry due to their low concentrations in municipal wastewater and high susceptibilities to degradation in aqueous environments. However, it should not be forgotten that COVID-19 is a novel virus and new information is being discovered each day.
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 is expected to pose no risk to treated drinking water. As the outbreak continues, more water-quality experiments are needed before major conclusions can be drawn on their fate within the environment. While this will be tricky, especially as viruses continue to 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.