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Changing the game

Innovative electrochemical process recovers ammonia from manure


July 2, 2024  by James Careless

The lab setup providing proof-of-concept of ammonia recovery and chemical production strategy. Images courtesy of University of Wisconsin-Madison

Ammonia losses are a problematic byproduct of manure.

In its gaseous form, concentrated ammonia can cause everything from acute eye and airway irritation to chronic asthma-like symptoms, decreased lung function – and in extremely high doses, death.

Gaseous ammonia can also be transformed to nitrous oxide, a greenhouse gas, while its deposition can acidify soils, damage and weaken plant life, and contribute to algae blooms in surface water.

Not surprisingly, the livestock industry is seen as a major source of ammonia emissions due to its output of animal manure. Although it is possible to reduce the amount of ammonia produced in livestock manure by adjusting the animals’ diets, there remains a need to mitigate the ammonia that is lost from manure to the atmosphere. This is why an innovative electrochemical process developed by researchers at the University of Wisconsin-Madison (UW-Madison) could prove to be a game-changer for manure management, and – by extension – the entire planet.

Their work was recently published in the journal Nature Sustainability under the name ‘Electrochemical ammonia recovery and co-production of chemicals from manure wastewater’, with an online posting date of December 8, 2023. 

How the process works
Dr. Song Jin is a professor in the chemistry department at UW-Madison. He is leader of the team that has developed this new ammonia recovery process, which is still in its laboratory testing phase.

Here’s how the process works. A sample of dairy manure wastewater is put together with a ‘porous battery electrode’ – specifically an ion-selective potassium nickel hexacyanoferrate (KNiHCF) electrode – that is capable of oxidizing organic materials within the manure mixture and absorbing the ammonium and potassium ions present in the manure liquid. “It essentially works like a battery electrode,” says Jin. “The spontaneous electrochemical reaction that occurs between the battery electrode and the organic matter in the manure drives the uptake of ammonium and potassium ions into the materials.”

Once this electrode has been saturated with ammonia and potassium ions, it is removed from the first container and inserted into a second container filled with a clean salt solution. An electrical current is applied to the electrode, causing it to release the ammonium and potassium ions into the solution. Once the solution has been evaporated away, the nutrients are left behind in dry form – ready to be used as nitrogen and potassium-rich fertilizers.

That’s not all: When the ammonium ions are released, “we can perform other chemical reactions on the other electrode in the solution to make products that are also useful and valuable,” says Jin. “One of the demonstrations we did here was to make hydrogen gas, which is a fuel. The other demonstration made hydrogen peroxide, which is a disinfectant that can be used to treat wastewater and do other things. These are very useful byproducts.”

In a single cycle, researchers found that up to 50 percent of the ammonia within the liquid manure could be recovered by this process. A second cycle brought the extraction level up to 85 percent. That’s no small achievement, and one that represents a significant reduction in manure-generated ammonia being released into the environment.

An inspired discovery
The inspiration for the electrochemical approach to ammonia removal came from fellow team member, Dr. Mohan Qin, an assistant professor with UW-Madison’s Department of Civil and Environmental Engineering. “She was the one who pointed out that people are interested in recovering ammonia from manure, that the current membrane-based processes to do so are inefficient and costly,” says Jin. “This motivated us to develop and test this new process.” 

The fact that this electrochemical process extracts potassium as well as ammonia is an added bonus. That’s not all: “It was also surprising that we were able to just spontaneously oxidize the organic matter in the manure,” he says. “We were not planning for that at the beginning, but we accidentally found out that this was happening once the process was underway. That’s actually not a bad thing at all, because if you don’t have this spontaneous action, you would have to run another complete electrochemical process on the uptake side driven by electricity. With this spontaneous oxidation reaction, we can skip that step and simplify the process.”

An illustration demonstrating the process through which ammonia is recovered.

Positive implications
The ability to extract ammonia and potassium from liquified manure has many positive implications for livestock manure producers, in specific, and the planet overall.

The first implication is potential profit for the livestock industry. Assuming that this laboratory process can be scaled up to an industrial scale, manure can become a source of revenue for livestock producers. For instance, a preliminary estimate by professor Fikile Brushett, a team member from the Massachusetts Institute of Technology (MIT), shows that a 1,000-dairy-cow farm could potentially earn up to $200,000 a year out of this process.

Dr. Rebecca Larson is a professor in UW-Madison’s Nelson Institute for Environmental Studies and a member of the research team. Her research indicates that this process could reduce ammonia losses to the atmosphere of this same herd by up to 50 percent, with potential revenue streams for this operation.

Larson also sees electrochemical ammonia recovery as a natural complement to manure digesters. “There’s been concerns expressed about digesters mineralizing nitrogen and losing more ammonia afterwards,” she says. “You could certainly pair these two together, so that one could offset the other.” Moreover, in such a pairing, some of the biogas being produced could be used to power both systems. This would be a ‘green’ option that could make such facilities more acceptable to adjacent property owners.

A further benefit of this ammonia/potassium extraction process is reducing the impact of manure by increasing options for end use management when nutrients are extracted. This could improve management during land application and reduce impact on nearby groundwater, plus flowing water in streams, rivers, and lakes. In turn, this process would reduce the effects of ammonia and potassium pollution on plants, marine ecosystems, and ultimately people.

Going industrial
The laboratory-based electrochemical ammonia recovery process is not yet ready for prime time. The biggest challenge that Jin and his teammates have to overcome is scale: equipment, electrical sources and infrastructure need to be there – but the process still must remain affordable and easy to install, run and maintain on a farm.

Of course, all of this will take money. The current research into this process is being funded by a National Science Foundation (NSF) grant (CBET- 2219089). But since NSF grants are focussed on bankrolling fundamental science and engineering research, other sources of money will be needed to move electrochemical ammonia recovery from the lab into farms.

This being the case, “we’re open to additional funding partners, even maybe business partners if there’s enough interest,” says Jin. “We are certainly open to starting a company to look at some of those practical things and develop a commercially viable process. As for our research, we have even more ambitious goals for this project. What we just published is just a preliminary step. We are aiming to further reduce the carbon dioxide emitted by digesters and other farming processes into useful chemicals and integrate that with ammonia recovery.” •

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