Coronavirus and the water cycle—here is what treatment professionals need to know

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 SARS-CoV-2—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. 

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 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 may be transmitted through human waste.

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 including disinfection to reduce the pollution impacts on nearby receiving waters like lakes and rivers.

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 SARS-CoV-2 has been detected in raw wastewater, and the virus is capable of binding to cells in the human gut. Further, in at least one study, SARS-CoV-2 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 SARS-CoV-2 viruses 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.

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 data is 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.