Israeli experts say that sewage plants in some developed countries need to add a step to their treatment, fearing that the coronavirus can make it through the process and be introduced into natural bodies of water.
“We’ve found that copies of the virus have survived after conventional sewage treatment, raising a concern that when treated wastewater is released to streams and rivers, it could infect animals,” Oded Nir, one of the scholars, told The Times of Israel.
He said that only one percent of coronavirus RNA survived in treated sewage inspected by his team, and researchers have estimated that SARS-CoV-2 can only remain active in untreated or inadequately treated wastewater for a few days.
However, the amount of virus and quick treatment time in sewage plants, which can turn dirty water clean in 12 hours, are enough to raise alarms.
“It’s hard to predict what this would mean, but there is a concern that this could cause reinfection from animals back to humans, possibly after a mutation,” said Nir, a researcher at Ben Gurion University’s Zuckerberg Institute for Water Research. “If we pump large amounts of the virus to nature without further treatment, it could impede efforts to eliminate the virus.
“There is also a concern that humans could possibly get infected directly from wastewater that has coronavirus RNA.”
Nir’s team says that a simple step, tagged on to the end of conventional sewage treatment, can eliminate remaining coronavirus RNA: disinfection, which is most commonly performed by chlorinating the water, but can be effected through other methods, including with ultraviolet light.
While many sewage plants add this step before pumping into rivers and streams, it is far from universal, even in the developed world.
A spokesman for Thames Water, which controls 68,000 miles of sewers and 5,235 pumping stations to process the sewage of 15 million Londoners, told The Times of Israel that it doesn’t chlorinate or add an equivalent step in its wastewater. Nir’s team cited documents from several other countries and cities that indicate similar absence of disinfection, including one suggesting that only 22% of Brazil’s treated wastewater is disinfected.
There are various factors that discourage disinfection. While it is highly effective as a hygiene measure, it adds cost and manpower requirements to sewage plants. There are also environmental considerations, which mean that in normal non-pandemic times Nir doesn’t advocate the practice. The chlorination method, which is considered the most cost-effective, can damage microorganisms and cause the release of chemicals in nature, he said.
Nir and microbiologist Ariel Kushmaro, who is also a researcher at Ben Gurion University of the Negev, are part of a team that took samples from Israeli sewage plants in order to study them. They found that the standard treatment, used in much of the developed world, eliminated 99% of coronavirus RNA.
Of the 1% that remains, existing research suggests that most doesn’t retain the ability to infect cells, but Nir says some of it may.
“While the amount of RNA remaining is small, if you think that a single drop can have 100,000 copies of the virus, you see there is a concern here.”
The researchers found that when adequate chlorine was added, as already happens in Israel, all traces of the virus were eliminated.
The Ben Gurion research, published on an online repository ahead of peer review, comes as scientists are increasingly noting that wastewater is something of a blind spot in coronavirus knowledge.
Water experts from Durban University of Technology recently published a peer-reviewed article that represents one of the most comprehensive studies to date.
Their research suggests, contrary to the Ben Gurion paper, that conventional wastewater treatment deactivates coronavirus particles, but they called for more investigation.
“Only one study so far has analyzed treated wastewater for coronaviruses,” they lamented. “The lack of interest could be attributed to the earlier belief that these viruses may not occur, and even if they do, will be in low viral loads in wastewater.
“However, the increasing evidence that this might not be the case calls for studies on how conventional wastewater treatment processes may either remove or inactivate coronaviruses,” they said.
The Durban scholars noted that live SARS-CoV-2 has been isolated from patients’ stools, in one case some 15 days after they developed COVID-19.
They cautioned that if live SARS-CoV-2 is in wastewater, it “may pose health concerns” for those who come in to contact with it, and wrote: “The present belief is that SARS-CoV-2 has a low infectious dose, therefore the viral loads in the wastewater could still pose a great risk.”
Kushmaro said his team’s conclusion that some coronavirus RNA remains isn’t “alarmist.” Though he recognizes there is no proof that water with coronavirus RNA can infect people or animals, he stressed that it also hasn’t been ruled out, and that, therefore, caution should be exercised and disinfection introduced in all plans where is isn’t already deployed.
“In Israel we add another very effective stage, after conventional treatment, namely chlorination,” Kushmaro said, “but in much of the world chlorine isn’t added, and we’re urging sewage plants worldwide to start adding it.”