College of Engineering News Room

Turning Coastal Communities into Clean Water Converters

by Russell Nay

Researchers in the Department of Civil and Environmental Engineering at USF are preparing to begin lab work on a project that could have significant impacts on where coastal communities, including Tampa Bay, source their clean water from.

The team, consisting of principal investigator Mauricio Arias, co-investigators Qiong Zhang and Nancy Diaz-Elsayed and Ph.D. candidate Joshua Benjamin, proposed a project focused on advancing pressure-retarded osmosis research, the PRO system, to the U.S. Bureau of Reclamation through their Desalination and Water Purification Research Program. The bureau, which manages, develops and protects water resources in service of the country, awarded the team a grant of more than $130,000 in July to carry out its three-stage project.

The goal of the project is to develop a system that improves existing reverse osmosis techniques and can be scaled to meet the water use needs of a variety of coastal cities across the country. Reverse osmosis is a water purification process and can be used in desalination, the process of turning saltwater to freshwater. This is useful for communities suffering from water shortages but with access to oceans. It’s also of interest to Tampa, which constructed a desalination plant that was — at the time in 2008 — the largest of its kind in the U.S.

The biggest issue with reverse osmosis is its cost and environmental impact. The process requires an extensive amount of energy to remove salt from water, and it leaves behind a very concentrated brine solution. This solution is typically pumped back into an ocean or bay, which may harm local aquatic ecosystems.

PRO works by capturing the potential energy in the salinity gradient that exists between saltwater and freshwater and using it to move electric turbines and generate power. The team hypothesizes that it is significantly more cost effective and has lower environmental impacts than the conventional reverse osmosis process, with hopes that a large-scale PRO system could work alongside existing reverse osmosis systems and become a useful resource for Tampa and communities beyond.

“This is primarily a USF project, and we’re using our desalination plant here as a case study,” Arias said. “Hopefully this system can be implemented here eventually. The folks at the Tampa Bay Water desalination plant are very excited about this project.”

Figure 2 from the project proposal

One of the key figures from the proposal to the Bureau of Reclamation, the graphic shows how the research team’s proposed PRO system could be integrated into the water treatment facilities connected to the Tampa Bay.

The project itself will be broken into three stages: identifying economically viable configurations of the PRO systems using an already completed computer model, implementing these findings into an advanced, laboratory-scale PRO system and evaluating the environmental and economic impacts of the enhanced model in Tampa Bay over time. Some of these tasks will take place simultaneously, and the project is slated to last until the end of March 2021.

The research team plans to split up each phase of the project with some overlap. Zhang and Diaz-Elsayed will lead the sustainability assessment portion of the project, while Benjamin plans to assist with the assessment but focus mostly on modeling and testing the advanced PRO system. Arias will be the project manager and focus on supervising Benjamin’s work modeling the advanced system as well as the rest of the project in general.

Figure 1 from the project proposal

Another key figure from the project proposal, this graphic visually represents the timeline of the research team’s proposed work throughout the life of the project.

“We’re coupling modeling with experimental research to evaluate prospective scenarios that are grounded by realistic process characteristics,” Diaz-Elsayed said. “We would like to investigate, from a financial standpoint and from an environmental standpoint, what are the associated savings we could achieve if we implement this system at larger scales?”

Zhang said that while there’s existing research on PRO systems, many other U.S.-based studies have been focused on the more experimental and theoretical aspects of the technology. PRO systems haven’t been commercialized or implemented for communities in the U.S. yet.

“I don’t think there’s any study really looking at an economic analysis (of PRO),” she said. “I think one unique aspect of this project is that it’s looking not just at the technology’s feasibility but at its economic feasibility. …We want utility companies to support and realize this technology.”

The project itself was selected to be a focus of Benjamin’s Ph.D. research. Zhang and Arias co-advise Benjamin in his Ph.D., and he said he’s always been interested in ocean renewable energy technologies. In the past, he helped Arias with a research project on the environmental impact of damming parts of the Mekong River in Cambodia for hydropower stations.

The preliminary model of the research team’s PRO system is similar to a system implemented in Norway in 2009 by renewable energy supplier Statkraft. The system was not economically viable, however, and was shut down in 2014. This facility — as well as the current Megaton Water System in Japan and an ongoing Korean-based study on optimizing PRO membranes — is what inspired Benjamin to initially scope research on the subject.

He also plans to present the team’s research at the 80th International Water Conference in Orlando — an annual conference on the latest scientific advances in water treatment around the world.

Joshua Benjamin Presenting PRO Research

Left: Benjamin presents PRO system research at the 2019 Association of Environmental Engineering and Science Professors. Right: Benjamin (left) is awarded a travel scholarship during his attendance at last year’s International Water Conference.

“I’m really thankful that Dr. Arias and Dr. Zhang allowed me to take my own path (with this project),” Benjamin said. “There’s been a lot of fundamental research on this technology, but people haven’t really looked at how this could be applied and how people in the industry can take this technology and implement it in their plants.”

Arias, Zhang and Benjamin have already submitted a paper to a scientific journal, which provides the baseline research of the funded project, and their lab work begins in October. The Bureau of Reclamation grant will also allow the team to support an undergraduate student research assistant, and they may take a mobile scale model of their PRO system to present at local schools early next year.

They’re also talking to key stakeholders at Tampa Bay Water to see if their future PRO system could significantly reduce their energy cost in providing clean water for communities throughout Tampa.

“If we’re able to — with this proof of concept project — show them that it’s feasible, perhaps we can think about going into the pilot scale,” Arias said. “Perhaps that will be the next phase.”