“Waste streams are an extra good fit for vertical farming and CEA in general for several reasons. Firstly, CEA has a predictable usage requirement that rarely changes as a result of the highly optimized method of growing. When valorizing a waste stream, it is vital to understand the demand and that the demand is continuous and steady. Secondly, our production is continuous throughout the year, where we compare to arable agriculture, which has seasonal requirements at set points throughout the year for things like fertilizer applications, vertical farming demand is continuous,” says Lilly Manzoni, Head of R&D at LettUs Grow.
As a part of a greater analysis, LettUs Grow is conducting research on using waste streams such as digestate from anaerobic digestors and other waste streams such as coco husk, which can be used in CEA generally, it is possible to apply these waste streams to arable agriculture too. Still, there are strict regulations determining the application of fertilizer to the field.
Lilly Manzoni is pictured third in the group photo.
The story began back in June, when Nicholas Pitts from the Scotch Whisky Research Institute met India Langley and Lilly Manzoni from LettUs Grow and Dr. Alexandros Stratakos, Associate Professor in Sustainable Agri-Food Production at UWE Bristol, at the AFN Network+ Crucible event in Bristol. The event was designed to bring together academics and food system stakeholders to collaborate and develop ideas around supporting agri-food to reach net zero.
From synthetic to anaerobic
LettUs Grow designs and builds aeroponic technology and farm management software for greenhouses and vertical farms. The farms require fertilizer all year round, with many growers reliant on synthetic versions, which are a significant source of greenhouse gas emissions. Developing more climate-friendly fertilizers is critical.
One possible alternative to synthetic fertilizers is to use digestate from anaerobic digesters. Digestate is in surplus due to the growth of the anaerobic digestion sector and is rich in nitrogen, phosphorus, and potassium - vital for plant growth. However, although digestate has been used as a fertilizer for arable crops, it hasn’t been used significantly in indoor farming systems.
“As a technology provider, we’re researching on behalf of growers who have a high reliance on synthetic fertilizer,” says Lilly. “That’s generally quite problematic because it’s a by-product of a chemical process and has quite a significant emissions profile. We can reduce our reliance on synthetic fertilizers by using digestate, but one of the challenges with that is establishing whether to use plant or animal-based digestate, as each has different nutritional profiles and safety considerations.”
It was India and Lilly’s interest in fertilizer and digestates that led them to Nick. “It was almost like a trading game,” says Lilly. “I remember Nick saying that Scotch Whisky has loads of digestate, what can we do with that? And we use fertilizer in our indoor farms, and it was like who could trade what with who.”
Trialing plant-based fertilizer on basil production
An idea was born to develop a project to examine the effectiveness of plant-based and animal slurry-based digestate on an indoor basil farming system, and assess them for pathogen risks and nutrient contents, and test their effectiveness against synthetic fertilizers. The plant-based digestate will be provided from a distillery anaerobic digestion (AD) plant. The project will also include a literature review to identify locations where indoor farms and anaerobic digestion plants could be beneficially combined.
“The Scotch Whisky industry produces a lot of digestate through our anaerobic digestion plants,” says Nick. “There’s a lot of research in applying digestates to arable farms, but there are limits on where and when you can use digestates in arable farming. With the cost of energy and a movement to circular economies, we might have quite a lot of digestate floating about, with only so much being able to be effectively utilized by arable farmers in the immediate surroundings of the distilleries. On the East Coast of Scotland, you’ve got distilleries and lots of arable farming, but in the future, if we have anaerobic digestion plants on the islands and on the West Coast of Scotland, where there is much less arable farming, it might make more sense for that digestate to go to more closed agricultural systems that help provide jobs and food to local communities.”
It’s this connection and synergy between the two sectors that excites the team.
“What we have at the moment with agri-food is quite a lot of people working in quite extreme silos,” says India. “There’s a really exciting opportunity here for connections. To have co-location of containerized farms situated close to anaerobic digesters or close to farms that are going to be providing the wheat for distilling. Controlled environment agriculture relies heavily on energy, depending on whether it's vertical farming, which is electricity-heavy, or greenhouses that use gas for heating. Being able to connect that with anaerobic digestion provides a lot of the resources we need along with fertilizer.”
Leading the project is Dr Alexandros Stratakos.“We’re bringing together not just academics but different stakeholders,” he says. “It won’t just be an academic exercise, the outcomes of the research will be able to more easily translate into changing practices that the industry can adopt, not just farming but the AD industry too. At the end of this project, we will have tangible, robust scientific data which will be needed to prove this is safe and feasible.”
Concluding the results obtained from the research, Lilly adds, "This brings the opportunity to drive circular economies within CEA, which are a vital part of the road towards net zero. By communicating with other industries, we can determine exactly what treasure you might find in someone’s trash!"