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Author: Dave Kiefaber
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Green seaweed sea algae covered stone in sea water, beautiful wet sea moss close up
“This is an exciting yet complicated project. Nothing similar has been attempted before. The team is multidisciplinary with electrochemists, microbiologists, and oceanographers, and all the pieces of the puzzle should come together during the deployment phase.” — Ruggero Rossi, assistant professor of environmental health and engineering

Ocean-deployed sensor systems serve vital roles in measuring water conditions and tracking marine climate change, but servicing the batteries on these energy-hungry devices is risky and expensive.

Supported by a two-year grant from the Defense Advanced Research Projects Agency, a team that includes a Johns Hopkins environmental engineer is developing systems that could power these devices using dissolved organic matter, plankton, and small algae found in seawater. This innovation could tap into marine biomass as an abundant energy source while reducing the expense and environmental impact of these systems.

“This is an exciting yet complicated project. Nothing similar has been attempted before. The team is multidisciplinary with electrochemists, microbiologists, and oceanographers, and all the pieces of the puzzle should come together during the deployment phase,” said Hopkins’ team member Ruggero Rossi, an assistant professor of environmental health and engineering, who joins researchers from James Madison University, Harvard University, the University of Maryland, the University of Delaware, and private industry on the two-year effort.

Rossi has previously scaled up a device to convert organic waste into electricity, but the system was used in easily accessible wastewater treatment plants and not in the middle of the ocean under 30 feet of seawater.

According to Rossi, the upgraded sensor design will consist of three parts: a filter, similar to fish gills, that opens upon deployment to collect biomass from the ocean; a fermenter that breaks the biomass down into smaller, easily degradable organic acids; and a microbial fuel cell where those acids will be transformed into electricity.

Rossi’s team will take the lead in designing the fuel cell reactor, optimizing anodic and cathodic processes for increased efficiency and energy output. Ideally, these improvements will enable an upgraded microbial fuel cell to deliver 0.01 kW of energy, enough to charge a cell phone. This is a significant increase for marine sensor systems, especially within the cell’s current weight and space restrictions.

Once a prototype is ready to deploy, it needs to be precisely placed for effective testing, Rossi says. Sending it too deep will deprive it of oxygen, and keeping it too shallow will deprive it of biomass. As a result, the team plans to deploy its first prototype off the coast of Lewes, Delaware. The team chose this location because of its proximity to the members who will be deploying the cell.

Rossi acknowledges that the task ahead is challenging.

“We have only two years to figure this out, which is far less time than the eight years assigned to prior scaling up projects on energy recovery from wastewater. We also don’t have the benefit of published research to guide us, as the proposed cell design has no precedent in any project of this scale,” he said.

However, he is optimistic about the project’s potential contribution to renewable energy technology.

“Marine biomass is abundant enough to increase the portfolio of energy sources, even if its waste-to-energy conversion potential can be optimized for broader application. The scope of this project, if successful, is as vast as the oceans themselves,” he said.