Simple purification clears coronavirus from water

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Existing water purification plants can easily reduce vast quantities of the coronavirus and protect household water, a new study suggests.

Among the many ways that viruses use to infect people, drinking water may pose only a tiny risk for spreading certain viruses like the novel coronavirus. However, in cases where there is unauthorized wastewater disposal or other events of inadvertent mixing of wastewater with water sources, the possibility of transmission through drinking water remains unknown.

For the new study, researchers used a surrogate of the coronavirus that only infects bacteria to show that the water purification step called coagulation can alone get rid of 99.999% of the virus, markedly decontaminating water for consumption.

“We did not want to wait till drinking water became a potential cause for concern for coronavirus transmission,” says Shankar Chellam, professor in the civil and environmental engineering department at Texas A&M University.

“This study shows that decontamination technologies that are already in place in water treatment facilities can remove or inactivate the coronavirus and other viruses that are structurally similar.”

Viruses fit into two structural type categories: those that have an outer fortress, called an envelope, and those that don’t. This envelope, which consists of a lipid bilayer and attached proteins, has multiple functions, including helping the virus enter host cells. Coronaviruses and Ebola virus both have a protective envelope.

Previous studies have found both enveloped and nonenveloped viruses in wastewater. However, most research has solely focused on the survival of nonenveloped viruses after wastewater and water treatment.

“It is well known that wastewater mixes with drinking water supplies. In fact, in many countries, including the United States, wastewater is purified and used as drinking water,” Chellam says. “If enveloped viruses persist in wastewater, there could be a minuscule chance that these viruses make it into our drinking water supplies. We just don’t know for sure.”

At treatment facilities, raw water generally undergoes a three-step purification process: coagulation, filtration, and disinfection. In the coagulation step, certain metallic salts are added to initiate particles suspended in water to join together into millimeter-sized clumps. These clumps then settle down as sediment and are easily separated from the water.

Chellam and colleagues tested to see if enveloped viruses also assemble into bundles during coagulation. For their experiments, they added a surrogate of the coronavirus that specifically infects bacteria to clean water. Next, they separately tested the action of a coagulant commonly used in water treatment plants.

After coagulation, they studied small samples of the virus-infused water under an electron microscope and found that the virus strain assembled on the coagulants, forming clusters. They then checked the presence of infectious viruses in the water after removing the clumps and they found there was a 100,000 reduction.

“The US Environmental Protection Agency mandates 99.99% of the viruses must be removed or inactivated from drinking water, and we found that even without filtration and chlorination, we were getting rid of 99.999% of the viruses,” Chellam says.

The researchers note that although they used the coronavirus surrogate for their study, the results are readily generalizable to other viruses that have similar surface characteristics, notably a lipid bilayer envelope and similar spike proteins.

However, Chellam says that in the real world, wastewater contains a whole slew of viruses, unlike their experiments that included just a single strain of virus. In their next set of experiments, they plan to investigate if coagulation is still as effective at decontamination in these scenarios.

“Our work suggests that surface water treatment plants might be already well equipped to meet virus regulations for drinking water,” Chellam says. “And coagulation is just the first step in the water purification pipeline. This is very encouraging since additional purification steps will only attenuate enveloped viruses further, alleviating associated health risks even more.”

The study appears in the journal Environmental Science and Technology. The National Science Foundation funded the work.

Source: Texas A&M University