For cleaner water, NSF taps CU applied mathematician


At the  75th Street Wastewater Treatment Facility are, from left to right: Chris Douville, the city of Boulder’s coordinator of wastewatertTreatment; Cole Sigmon, process optimization specialist; David Bortz, assistant professor of applied mathematics at the University of Colorado Boulder. Photo by Noah Larsen.

By Clint Talbott

Wastewater-treatment plants might be able to send consistently cleaner water downstream if the newly funded work of a CU-Boulder applied mathematician comes to fruition.

David Bortz, assistant professor of applied mathematics at the University of Colorado Boulder, has won a three-year, $485,886 grant from the National Science Foundation to improve micro-scale mathematical models to predict the conditions under which microbial clumps form during wastewater-treatment.

The goal is to help wastewater plants clean the wastewater more efficiently, as well as emit cleaner water.  As a consequence, downstream water-treatment plants could spend less energy and fewer resources cleaning the water to meet standards of drinkability.

As he refines his mathematical models, Bortz will work with Chris Douville, the city of Boulder’s Coordinator of Wastewater Treatment, who manages the 75th Street Wastewater Treatment Facility, where the models will be implemented and tested.

Microbes such as bacteria suspended in water do not generally live as single cells. “By collision and separation, they combine and recombine in a process called flocculation,” Bortz writes. Flocculation, which regularly occurs in laboratories, manufacturing facilities and wastewater-treatment plants, “has a surprisingly large impact on human life,” Bortz notes,

For reasons not entirely clear, “populations of flocculating microbes sometimes crash, with the clumps becoming too large and settling to the bottom.” Then, the wastewater plants are much less efficient at processing wastewater.

“So if we could understand mechanisms for why that happens, we could develop inexpensive strategies to produce cleaner water, and do so more efficiently.”

Sophisticated mathematical models, like those used to forecast weather, try to account for a wide variety of complex and changing conditions. In the case of wastewater, that is not generally the case. However, treatment-plant operators observing bacterial clumps through microscopes regularly report that the clumps tend to look different when the emitted water is clean and when the water is not as clean.

“At present, none of the mathematical models fully accounts for flocculation,” Bortz notes. An existing model, the Activated Sludge Model, describes the dynamics of phosphate, ammonia, nitrogen gas and the like—but this is a large-scale model.

“The Activated Sludge Model, now in its third version, is very good,” Bortz says. However, “My opinion is that you can probably double the efficiency by fully accounting for flocculation.”

Scientists’ understanding of how multi-cellular colonies form, grow, fragment and disseminate is “still in its infancy,” Bortz says.

The aim is to transform scientists grasp of microbial flocculation from “one based upon simplified, idealized models of clusters to one based on the microscale mechanistic and metabolic first principles,” his grant states.

Better understanding the behavior of populations of microbes could lead to “dramatic improvements in many diverse societal challenges—from biofuel production efficiency, to sustainable means of handling wastewater to management of oceanic algal blooms,” Bortz writes.

“The wastewater-treatment focus will be the most immediately applicable result of the work,” he observes. Optimally, a new model that accounts for flocculation would give wastewater-treatment-plant operators greater understanding and control over their work.

Depending on the conditions of the water, and the predictions of the Bortz models, plant operators could make appropriate adjustments, ranging from varying the levels of additives, increasing or decreasing aeration or activating propellers to break up the clumps.

“These are all variables that you can optimize experimentally, but if you could do it in a more systematic way, you could get substantially cleaner water out.”

In addition to integrating some of this work into his Mathematical Biology course Bortz teaches every spring, Bortz’ grant also includes outreach activities at the Boulder’s Southern Hills Middle School and the Rocky Mountain Water and Wastewater Plant Operators School.

“This effort is designed to help students at all levels understand how practical math can be, how it can be used in the real world, and why they study it,” Bortz adds.

In that context, the goal is to connect some of Bortz’ research with everyday applications, such as insight on how to control the populations of microbes.

Bortz directs a research group of two post-doctoral researchers, four graduate students and one undergraduate student.

Bortz’ project, “Microbial Flocculation Dynamics,” is in collaboration with microbiologist John Younger, at the University of Michigan. It is being funded by the NSF Division of Mathematical Sciences (Mathematical Biology section) and co-funded by the NSF’s Division of Biological Infrastructure within the Directorate for Biological Sciences, and the Chemical, Bioengineering, Environmental and Transport Systems within the Directorate for Engineering.

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