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Miniature Northern Lights - in hydroponic greenhouses

14 October 2021 - Source : BLOG

 


By exposing a gas to electric field, plasma, the fourth state of matter, is created. (Photo : Sean Watson)

 

In a greenhouse on Montréal's North Shore, Stephan Reuter will soon be testing a device likely to accelerate plant growth, assist plants to combat pathogens, and above all reduce greenhouse crops’ carbon footprint. What is this incredible new technology? Well, here's a hint - it's based on the same state of matter found in the Northern Lights, and the same state of matter which illuminates certain lit signs in the dark. It's plasma! Wait, what?

The pandemic awakened Quebecers across the province to the importance of food autonomy, and the need to increase the local production capacity of fruits and vegetables to something closer to 12 months a year.

The provincial government shares this line of thinking, and provided the industry with financial support in the form of subsidies and preferential electricity tariffs, The government even went as far as setting the goal of doubling greenhouse growing surface area in the province within five years.

Meanwhile, Polytechnique Montréal's Professor Stephan Reuter (Department of Engineering Physics) has his mind set on another important issue. In the company of collaborators from various fields of expertise, notably Caroline Côté (Institute for Research and Development in Agri-Environment - IRDA), Professor Jason R. Tavares (Polytechnique Montréal) as well as Les Serres Lefort, Reuter is trying to develop a technology likely to improve greenhouse production conditions while reducing their carbon footprint.

You may not know it, but growing fruits and vegetables in greenhouses comes with an environmental cost that isn’t just limited to the energy used to heat, ventilate, and light buildings - the use of synthetic nutrients are also a key concern when it comes to carbon footprints.

Nitrogen is a great example of the above. Even though the air is 78% nitrogen gas, plants are unable to capture that gas directly in order to grow. Instead, their roots do the work, using nitrogen molecules from the decomposition of organic matter. At the turn of 20th century, farmers  were presented with an alternative to manure in the form of the industrial Haber-Bosche process, a process that ‘fixes’ atmospheric nitrogen in combination with hydrogen, to create the compound ammonia. 

Professor Stephan Reuter (Photo : Polytechnique Montréal)

“The problem is, this process has a considerable carbon footprint because it relies on the use of fossil fuels in addition to requiring high temperature and pressure,” explains Professor Reuter. Ammonia manufacturing plants alone are behind 1.4% of global CO2 emissions on Earth, in addition to consuming 1% of global energy.

So its clear that scientists and researchers are keen to find an alternative. Professor Reuter's plan is to bet on plasma, a state of matter obtained by supplying energy to a gas in order to extract electrons from the molecules therein, thus creating charged particles. Sun and other starts are made of plasma, so are the Northern Lights and lightning bolts.

In all of these cases, whatever the material is, it’s temperature is in the thousands of degrees Celsius. However, there is also a way to create plasma under ambient temperature conditions using electric fields, and Reuter is banking on this "cold plasma" approach for his research. “Cold plasma allows us to consider all kinds of applications involving biological material without the risk of destroying it,” he explains.
 

At a glance at... PLASMA

The process Professor Reuter envisions would make it possible to create, using only water and air, a multitude of unstable molecules with antiseptic properties such as ozone (O3), hydrogen peroxide (H2O2) and nitric acid (HNO3). The process would also make it possible to manufacture nitrate (NO3-), a source of nitrogen favoured by plants. (IMAGE: Professor Reuter's laboratory; plasma source picture by Julien Bissonette-Dulude)

Heat a solid, and it will turn into a liquid. Heat it even more, and it will become gas. Add even more energy and it will become plasma. This fourth state of matter is obtained when an excess of energy accumulated by molecules causes the release of electrons. The result is a series of ionized molecules capable of causing chemical reactions. Rather than heating gas to form a plasma, scientists use an electric field.

By ionizing air and water using an electric field, nitrate (NO3-) is formed - a molecular form of nitrogen that could potentially replace ammonia – and most importantly, can be assimilated by plants. A handy side-product are antiseptic molecules also known as reactive oxygen species (ROS) like ozone and hydrogen peroxide. The latter dissipate quickly, but researchers plan to use them to benefit plants, by exposing greenhouse water to these molecules in order to eliminate bacteria, fungi and viruses. These bi-products can also be used directly in order to stimulate plant growth, a contribution that has already been proven in scientific literature.


multiple Roles

Researchers from Polytechnique Montréal and IRDA will first test their theory in Les Serres Lefort's greenhouses where lettuce is grown. (Photo : Laurie-Anne Thuot)

Yet Professor Reuter's team is under no illusions - replacing a process that agriculture has relied on for over a century won't be a simple affair. "Cold plasma-based processes are still far from being more efficient than the Haber-Bosch in terms of producing assimilable nitrogen in large volumes," he says, adding that the 100-year old process has benefited from years of optimization.

“While not competitive strictly based on the nitrogen aspect alone, our approach could still be interesting if we also consider the bi-product antiseptic properties, and their ability to stimulate plant growth from ROS without the need of fossil fuels," he adds, pointing out that the process would also be used in the same place where fruits and vegetables are grown.

Given that the project is in its early stages, Professor Reuter prefers not to disclose exactly how the water will be exposed to the plasma, but one can already imagine that everything would occur in an enclosed space.

Professor Reuter’s team is currently working to determine which parameters to use to optimize the production of various molecules in plasma. "We want to understand what type of molecules we produce, but also how we can optimize production of molecules most useful to plants," he says, adding that the process will eventually be scaled up to be tested directly on plants in greenhouses.

“One of the challenges we'll have to overcome is the efficiency of the process,” he notes. “We're not talking about ionizing argon here: all we have as a starting material is air, water, and electricity."

From people to plants... APPLICATIONS IN MEDICINE LEAD TO THE GREENHOUSE

Professor Reuter has been interested in plasma’s potential applications in agriculture since 2016, when he was based in Germany. However, it’s plasma’s applications in the biomedical field that take up the most of his time, given that Professor Reuter holds the TransMedTech Research Chair in Plasma Medicine.

“For example, cold plasma could also be used to accelerate skin healing due to its antiseptic properties, but also offer new therapeutic strategies for some forms of cancer treatment.  Numerous avenues of application are being considered," he notes.

Learn more

Professor Stephan Reuter expertise
Laboratory web page
Department of Engineering Physics (In French only) web page

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