The Science of Sludge: Tala Navab-Daneshmand

Tala Navab-Daneshmand, right, works with undergraduate student Gabi Garza in the greenhouse.
Tala Navab-Daneshmand, right, works with undergraduate student Gabi Garza in the greenhouse.

Tala Navab-Daneshmand has made a career out of wastewater sludge.

“I sometimes joke that I am ‘The Poop Scientist,’” Navab says. “But it’s an accurate description.”

An assistant professor of environmental engineering, Navab examines the persistence and growth of enteric pathogens from wastewater in the environment, with an eye toward designing better treatment and handling processes. Enteric pathogens – including viruses, bacteria like E. coli, and other microorganisms – are a leading cause of diarrheal disease, which kills more than a half-million children each year, according to the World Health Organization.

After wastewater is treated, the resulting sludge may be further treated to become “biosolids,” used as fertilizer in agriculture. So, Navab follows pathogens in these biosolids from the wastewater treatment plants to their receiving environments, to see whether they end up in crops that are harvested and, ultimately, whether they end up on our plates.

She also follows enteric pathogens in low-income settings in the developing world, tracing their paths through water and soil, onto hands or food crops, and into homes and kitchens, to see how they are transmitted within these environments, with a focus on preventing diarrheal disease.

Originally from Iran, Navab was trained as a civil engineer, working on dam construction and hydropower plants in Tehran before pursuing a master’s degree in environmental engineering. That’s when she discovered her passion for pathogens. Prior to that, she says, she had zero interest in biology, which she remembers as her least favorite course in high school.

“I think I can say I hated it,” Navab says. “And then I took this microbiology course during my master’s, and it was so interesting to me. All these bacteria and microorganisms, I just loved them, so I studied them more.”

Navab went on to earn her Ph.D. from McGill University in Montreal, examining the inactivation of bacterial pathogens through de-watering of biosolids. She then did a postdoctoral fellowship with Eawag Water Research Institute in Switzerland, where field projects took her to Bangladesh and Zimbabwe.

Today, Navab’s work looks mostly at E. coli, which is a reliable indicator of fecal contamination when evaluating water for microbiological quality. Her research focuses in particular on a phenomenon called regrowth.

“This doesn’t happen with viruses. If you kill viruses, they’re done,” Navab says. “But with bacteria, you can kill them – you think you’ve killed them – but they can grow back. And there are many different reasons why they grow back.”

For example, biosolids applied to agricultural fields have to meet certain standards for microbiological quality. However, Navab says, testing of biosolids at the treatment plant won’t necessarily ensure that biosolids will still meet those standards weeks or months later, when they are applied to the soil.

“The reason is these bacteria have food available,” Navab says. “And then, depending on many other environmental conditions – moisture content, temperature, pH, all these different things – they can grow back. Even with standards defined for the time of application, what happens to these microorganisms when they are in the soil?”

A specific area of interest for Navab is the persistence and regrowth of antibiotic-resistant bacteria. These so-called superbugs pose a vexing challenge in the fight against infectious disease because they are immune to the front-line treatments health professionals have come to rely upon.

“This is a newer field,” Navab says. “There are no regulations specifically concerning antibiotic-resistant bacteria in biosolids for land application. We also are not quite sure of how they impact human health. We know that getting infected by antibiotic-resistant bacteria is not good. But we don’t know how they are transmitted to humans.”

One current project, undertaken in collaboration with Joy Waite-Cusic in the Department of Food Science and Technology, is looking at the application of either biosolids or of non-traditional sources of water for irrigation in agriculture. The project will examine whether antibiotic-resistant bacteria are introduced to the field through either of these sources, how these bacteria persist in the soil during the growth season, and whether they end up on crops (farm to fork).

The first step involves little pots of basil growing in a greenhouse on campus. The plants have been set up in different control groups and test groups, some using wastewater sludge as a fertilizer, and some inoculated separately with antibiotic-resistant bacteria. Samples taken during the growth season and of the finished crop will be analyzed in the lab to quantify antibiotic-resistant bacteria, using culture-based techniques and molecular methods.

Another project is looking at septic sludge in residential households in Vietnam, where 80 percent of households have septic tanks. For the most part, the sludge from these tanks is disposed of without treatment, directly into some sort of receiving environment – landfill, surface water, fish ponds, or agricultural fields. Navab and her collaborator in Vietnam, Mi Nguyen, will examine if pathogens from wastewater sludge end up in agricultural crops or in the flesh of fish consumed by humans, or if there is a risk to children who swim in contaminated water.

“If that’s the case, we can look at using a treatment process that is appropriate, economical, and practical for that setting,” Navab says. “We have been talking about, for example, anaerobic digestion, but then first we have to figure out what exactly is the situation.”

The issues surrounding safe food and water go beyond wastewater treatment and include economic and cultural factors such as education, sanitation, and handwashing practices. Navab warns against the appeal a technological quick fix or a one-size-fits-all solution.

“As engineers alone, I don’t think we can solve the problem,” Navab says. “People from different fields need to work together, and this is where interdisciplinary work really matters. People from many different fields – social sciences, engineering, public health, medicine – should come together and try to understand the problem, the culture, the community, and then define interventions that work for that specific society.”