New York, Jul 7 (IANS): Researchers have found that the microbe-laden "biofilms" that cling to sewer walls often contain harmful, antibiotic-resistant bacteria and can withstand standard treatment to disinfect sewers.

The study, published in the journal Environmental Science: Water Research & Technology, also revealed that cleaning with bleach can reduce the density of biofilms but not entirely remove them, potentially leaving wastewater treatment workers and the public exposed to health risks.

"Given the current interest in wastewater-based epidemiology for monitoring the coronavirus, our study highlights the need to consider sewer processes and how best to combat pathogens," said senior author Nicole Fahrenfeld from the Rutgers University in the US. For the findings, the research team examined the microbe-laden "biofilms" that cling to sewer walls and even built a simulated sewer to study the germs that survive within.

They found that these biofilms often contain harmful, antibiotic-resistant bacteria and can withstand standard treatment to disinfect sewers. Cleaning with bleach can reduce the density of biofilms but not entirely remove them, potentially leaving wastewater treatment workers and the public exposed to health risks, the study said.

According to the researchers, disinfecting a sewer line may be a good idea before sewer maintenance is done, especially following events such as a disease outbreak or bioterrorism incident that might expose sewer lines to high-risk microbes. "Luckily, with respect to SARS-CoV-2, the coronavirus causing COVID-19, water and wastewater are not expected to be important transmission routes," the researcher said.

"Normally, what's flushed down a toilet goes to a wastewater treatment plant. But rainfall can cause overflows of untreated waste into bays, rivers, streams and other waterways," they wrote. The researchers said a potential worst-case scenario would be an infectious disease outbreak following a sewer overflow that releases wastewater, sewer solids and biofilms to surface water.

"We will work to repeat a portion of our experiments to understand how long the coronavirus may linger in sewers and if that will impact monitoring of it in wastewater," Fahrenfeld noted.