Closer to source means faster, clearer results from wastewater surveillance

By David Nesseth

Standing in traffic to get a wastewater RNA sample through a sewer maintenance hole may not be ideal, but it may be more effective, suggests Dr. Banu Örmeci, director of the Global Water Institute and professor at Carleton University, who shared her research at the Toronto Wastewater Surveillance Conference in February this year.

The in-person and virtual event was organized jointly by Ontario’s Wastewater Surveillance Initiative and Toronto Metropolitan University, and brought together renowned experts to reflect on how monitoring expanded during the COVID-19 pandemic, and to predict where the field may be headed.

While logistically, there is a simplicity to obtaining and monitoring samples directly at the wastewater treatment plant (WWTP), easier does not always mean better, explained Örmeci in her conference presentation.

“It’s a bit of a pain,” says Örmeci of moving closer to the source, otherwise known as an upper sewershed monitoring location. “If this is the maintenance hole a sample is needed from, you may find yourself in wild vegetation, or the middle of traffic.”

Wastewater-based surveillance uses wastewater as a representation of all individuals within a sewershed and has previously been used to track the presence of poliovirus, antimicrobial resis- tance, and illicit drug use.

It takes some initial legwork, but Örmeci says that upper sewershed sampling locations to study viral loads must be selected carefully and considerations must be made around sewer design and hydraulics to get the best results. Testing teams must also consider elements such as sewer pipe connections and layout, flow rates, dilution from stormwater, total pipe distance, and wastewater travel times, known as “residence”.

While a more densely-populated country such as the U.S. may have a median wastewater residence time of 3.3 hours, Canada’s capital city of Ottawa, for instance, can have residence times of up to 36 hours. This is, in part, due to sewer network design, says Örmeci. “We have the habit of going further and connecting communities that are really too far away.”

The longer wastewater stays in the system, or the further it must travel, the viral signal in it will see some degradation prior to testing. It also introduces more stormwater, ice melt and other sewer sediments to the sample, says Örmeci. This is why going closer to the source can bypass these problems.

Apart from some logistical challenges, there are other clear benefits to sampling viral signals closer to the source as opposed to sampling at WWTPs, Örmeci explained. One study, based in Ohio, has also shown evidence that the age of a sewer system may also negatively impact the quality of a wastewater sample.

One of the most effective approaches that Örmeci has utilized for upper sewershed monitoring is called a nested community approach. She defines it as an area with particular population dynamics, where viral and behavioral trends often happen quicker than some quieter communities. These communities can often be a good indicator of viral trends in a larger general area, she says.

In one particular study, Örmeci demonstrated how the nested community approach was used to monitor Monkeypox. While the actual name of the community was withheld, she showed how much faster researchers were able to get quality, actionable data compared to sampling at the WWTP.

In May 2022, the upper sewershed monitoring detected Monkeypox 10 days prior to the local health unit’s own findings. For influenza, upper sewershed monitoring showed wastewater signals three weeks prior to the city-documented rise. Lastly, upper sewershed monitoring detected RSV some five weeks earlier than nearby health units.

“It allows us enough time to prepare to take necessary steps,” Örmeci says. Her line graph data from the nested community approach also showed how much stronger the viral signals were compared to the findings from diluted WWTP samples.

“Sampling closer to the communities minimizes the dilution and degradation of the viral genetic material in the sewer and helps us to provide more specific and actionable information to public health officials,” says Örmeci in a follow-up email with ES&E Magazine.

When Örmeci shared her data from the WWTP samples, she analyzed many characteristics of the infrastructure, such as the length of the sanitary and combined sewers, the number of pumping stations, as well as average and maximum flow rates, and the size of the population served.

Örmeci serves on the Strategic Council of the International Water Association. She is also the Jarislowsky Chair in Water and Health at Carleton University, and has earned more than 25 research, teaching and mentoring awards and recognitions.