UMN campus by Mississippi river

Professor Ray Hozalski and his team are pilot testing several treatment options to keep your water safe and tasty

Minneapolis Water Treatment and Distribution Services sought out University of Minnesota Civil, Environmental, and Geo- Engineering Professor Ray Hozalski and asked him to help improve the smell and taste of the city’s drinking water.

Complaints about the smell and taste of water are common in cities that get their water from a surface source. Minneapolis water comes from the Mississippi River. Surface water can contain byproducts of the growth of algae and cyanobacteria that affect the aesthetic experience of drinking water, even though the treated water is completely safe to drink. Usually, the presence of harmful microbes (i.e., pathogens) does not affect the taste or odor of the water, yet cities can entertain many complaints about water “quality” based on the people’s experience.

Hozalski is accomplished in solving this kind of problem. The City of Saint Paul was getting a lot of complaints about the taste and smell of its water. St. Paul Regional Water Services spent considerable time dealing with those complaints. The water was safe, but the earthy-musty smell and taste (think dirt or soil) were still negatively impacting the experience for St. Paul residents.

Hozalski and his team pilot tested several treatment options including ozone and granular activated carbon filters. Hozalski recommended that St. Paul install granular activated carbon filters to capture the compound geosmin, which was causing unpleasant odors and tastes. After implementing the GAC filters, the number of complaints dropped instantly and dramatically. The graph shows the number of complaints related to water taste and smell in St. Paul by year. Numbers fell after the implementation of granular activated carbon filters (shown by vertical line).

graph showing number of complaints filed regarding St. Paul Water

Minneapolis hopes that Hozalski can bring similar relief related to the water quality complaints they receive.

The raw water quality in Minneapolis, however, is more variable than what St. Paul experiences and that presents unique challenges. Although both cities ultimately get their water from the Mississippi River, the St. Paul supply is passed through a series of lakes before entering the water treatment plant. These lakes act as large settling ponds that remove many of the particles in the water, resulting in a pretty clean and consistent input into the city water supply for St. Paul.

In Minneapolis, water is taken directly from the Mississippi River. Because the river is directly impacted by stormwater runoff and snow melt, the resulting input to the water treatment plant in Minneapolis has higher levels of variability in terms of suspended solids and dissolved contaminants. That variability requires more diligence to maintain a consistent quality of drinking water.

Hozalski is confident that the taste and smell of the water can be improved, yet safety and sustainability (not aesthetics) are the most important drivers for any water treatment changes. The Minnesota Department of Health must ultimately approve any changes to the water treatment procedures. Their primary concern is that the water is safe to drink. Thus, any system changes implemented to address smell and taste issues must not negatively impact the removal of disease causing particles (i.e., microbes) from the water.

Yet Hozalski is not content to stop with safe water, or even pleasing water. After ensuring that the water is safe (monitoring the removal of particles and pathogens) and improving aesthetics (better smell and taste), Hozalski and his team will also endeavor to remove trace organic contaminants through granular activated carbon filters. There is rising concern about the occurrence of pharmaceutical compounds and other so-called emerging contaminants in waters throughout the United States. Although no documented health problems have been associated with these contaminants, some concerns have been raised in the popular press.

Hozalski’s study will dose and track eight particular trace contaminants and determine if the GAC filters can remove those trace contaminants. Minneapolis has no current problems with trace organic contaminants in the water supply, so this effort is a proactive study to determine if the new granular activated carbon system will provide this additional benefit should levels in the river increase in the future. The setup of granular activated carbon filtration columns for the experiment is shown.

GAC filtration columns for experiment

Ray Hozalski is the primary investigator on this project, but it takes an entire team to address all the interconnected parts of this complex project. Ben Ma, a graduate student, will work with Hozalski on the research. Professor Tim LaPara will advise on issues related to assessing the bacterial communities that colonize the granular activated carbon filter media. He will help the team to assess which bacteria are present and what they are doing. Professor Bill Arnold will advise on the analysis of the trace contaminants fed into the test system. Arnold helped to choose which contaminants to study and how to best analyze for them.

Hozalski values such projects for the connections and collaborations as well as for the ultimate outcomes. “The cool thing about doing research with the city utilities is that we have real impact on the lives of Minnesota residents. The Minneapolis Water Treatment and Distribution Services supplies water not only to Minneapolis, but also to the suburbs, about 400,000–500,000 people. I do basic research, too, and I enjoy it; basic research is important and often leads to fundamental discoveries. But practical problems like this produce locally impactful results that also yield valuable contributions to the broader scientific community.

“Cool science, real impact, publication in top tier journals, academic cachet, impact on student learning, a real legacy, and fun—that is the holy grail of engineering research!”

“Another great benefit of working with the city utilities is a chance to be in the water treatment plant regularly, to get to know the details of the plants and the challenges they face. I bring that experience back into the classroom, where it has been hugely helpful for teaching my students, particularly in the undergraduate water and wastewater treatment class.”

“These collaborations are helpful for the city utilities also. It is a win-win.”

Reprinted from the Department of Civil, Environmental, and Geo- Engineering CEGE News.