Imagine the day when a pickle factory, instead of dumping its saltwater waste, can use it to power the factory instead. Imagine that chemical process repeated on a much larger scale, using many rivers flowing into oceans to power the large portions of the country.

Thanks to work being done by UNC system researchers at the Mt. Olive Pickle Company in Mount Olive, NC, those scenarios are a step closer to becoming reality. Researchers from NC State University, the University of North Carolina at Chapel Hill, East Carolina University and the Coastal Studies Institute are developing a process that uses salinity gradient to release energy. The process is at the cutting edge of renewable energy, and could theoretically one day be used to generate one to three terawatts of energy – about half the electric power produced worldwide.

Transcript of “Salinity Gradient Energy”
UNC ROI: Research Opportunities Initiative

Kevin Campbell: Mount Olive, North Carolina is very much small town North Carolina. Members of the town in 1926 came together to form Mt. Olive Pickle Company, and the pickle company’s had a strong place in the community’s history. I’ve been impressed since day one, primarily with people. From the lowest paid operator right on up through the executive chairman. They work hard at their job.

My name is Kevin Campbell, I am the Environmental Supervisor for Mt. Olive Pickle Company. Our biggest challenge is we use a lot of salt, and so that means we discharge a lot of salt. My original call to NC State was trying to find anyone who may have an idea for beneficial reuse of some of our brine material and waste water material.

Douglas Call: My name is Doug Call. I’m an assistant professor of environmental engineering at NC State. I’m working on a collaborative project funded by the UNC ROI to investigate the potential for salinity gradient energy production in North Carolina. So this is a multi-institution project. Myself at NC State, my collaborator Orlando Coronell at UNC-Chapel Hill, Andy Keeler at East Carolina University, Lindsay Dubbs at the Coastal Studies Institute and Joe DeCarolis at NC State. So when we use the word salinity gradient what we mean is if you have two solutions and one solution has more salt than the other, then you have a gradient. If you put the two together they are going to slowly mix, and really it’s that mixing process that happens spontaneously that releases energy and so that’s what we focus on, is a technology called reverse electrodialysis that can recover salinity gradient energy.

Kevin Campbell: When Doug Call arrived, I guess it’s been a year ago now, I took him around back to show him the wastewater facility and walked him through step by step the processes. He had an idea for some of our brine material and wastewater material.

Douglas Call: The ingredients there at the Mt. Olive wastewater treatment plant were perfect for testing in the kinds of systems that we are working with. We’re going to be looking at three specific functions that RED systems can do. The first is electricity generation, the second is energy storage, the third component of the project is wastewater treatment. At the heart you’ve got a series of membranes, and these membranes are simply just material that only lets certain ions pass through. If we put in a channel and fill it with sea water, on one side we have a membrane that only lets things that have a positive charge go through. Sodium, for example. On the other side of that chamber we have a membrane that only lets chloride ions pass through, the negative charged things. On the other side of those membranes you have fresh water. Well the seawater, all those ions, they want to get into the freshwater, but they can’t because there is a selective barrier only letting certain ions through. And during that process you create a flow of ions in the system, but in order to actually make electricity we have to convert that to electrons. And so at two terminal ends of this whole system, you have electrodes which convert the flow of ionic current into electrical current. So if you integrate an RED system into a device called a microbial fuel cell, we can simultaneously degrade wastewater and generate electricity.

Kevin Campbell: He put it pretty much in layman’s terms that he wanted to make a big battery out of wastewater. Wastewater in general, as a rule, uses a lot of electricity. To have the ability to generate electricity to help offset some of that cost that would be a huge benefit.

Douglas Call: Salinity gradient energy technologies are at the cutting edge of renewables. Nowhere else in the U.S. currently has the size of the research team and the focus on this topic like North Carolina does. Why I’m so excited to be here at NC State and in North Carolina is the fact that there is support and funding to keep pursuing these dreams of out of the box technologies that can provide renewable energy and wastewater treatment.

Kevin Campbell: It’s a benefit to be in such a close proximity to two universities. They are usually involved with cutting edge ideas, ideas that are outside of the box. And you can build off of their experiences and possibly learn of a new idea that can help you change your process to be more efficient, to be more cost effective, to be better to the environment, to benefit the community at large.

Douglas Call: All of the energy that’s available where fresh water rivers dump into the oceans around the world, we could potentially generate anywhere from one to three terawatts, so that could potentially power almost half of the total electricity that’s produced today. This is a potentially inexhaustible and continuous resource for electricity generation.


Kevin Campbell
Environmental Supervisor, Mt. Olive Pickle Company

Doug Call, PhD
Assistant Professor of Environmental Engineering, North Carolina State University

Joseph DeCarolis, PhD
Associate Professor, North Carolina State University

Orlando Coronell, PhD
Assistant Professor, the University of North Carolina at Chapel Hill

Lindsay Dubbs, PhD
Research Assistant Professor, the University of North Carolina at Chapel Hill
Coastal Studies Institute

Andy Keeler, PhD
Professor at East Carolina University
Coastal Studies Institute

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