Closing the loop is what vertical farms should help us do. More specifically, vertical farms can be organs within their surroundings, turning nutrient-containing waste into high-value produce.

One of the ways I am exploring this idea is by participating in Wageningen University’s Greenhouse Challenge. I have already learnt quite a bit, and wrote an article about energy efficiency in greenhouses. But that week, we also had a webinar on using the nutrients in waste to produce food. It was very interesting but I never got round to writing an article on that. So, that’s what this is about.

AMI (aquaponics-mushrooms-insects) systems are great at turning food waste (and theoretically, faeces as well) into food. However, they might not be the only approach to closing the loop, for multiple reasons:

Some waste streams have contaminants which need removal. Not all waste streams have enough energy in them to be worth giving to an AMI system.

The Environmental Technology Group at Wageningen University is working on technical solutions for nutrient recovery. During this webinar for the Greenhouse Challenge, two people talked about this.

Prof. Huub Rijnaarts

Professor Rijnaarts talked about different technologies and the progress in their development at the moment. He distinguished two types of technologies:

Biorecovery technology – using life to add value, like AMI systems. Examples: fermentation, electricity, crystallisation, wood oxidation, cyanophosphate crystals, using urine to produce electricity. Water technology – this is about removing contaminants, such as pathogens and excess sodium. Hormones in our water is another big problem. Luckily they can be completely removed, but this requires a lot of energy.

He then mentioned some specific examples of nutrient recovery and their limitations. Some examples:

Phosphate can be recovered using aluminium and/or iron, but it results in a useless precipitate.

Calcium phosphate can be produced using fermentation, but this process isn’t perfect yet.

Phosphate, magnesium, and ammonium can be recovered together to make a good fertiliser, but this fertiliser dissolves slowly, making it impractical.

Looking further back, there are other approaches. By designing buildings differently, we could make the task of nutrient recovery easier. Simply separate the different flows within buildings, so that they never mix in the first place.

What are the next steps? The individual technologies are almost perfect. Integrating them together and scaling up will be the next challenge. Professor Rijnaarts mentioned a building in the Dutch town of Sneek which has been using principles like these for almost a decade. Most – if not all – of the problems have been ironed out.

Luuk Graamans

Rather than covering the specific technologies, Luuk talked about the way we should be looking at our resource flows. First of all, he said that we must integrate agriculture into all of our resource flows, and not see it as a separate activity. Zjef Van Acker would certainly agree – AMI farms are an organ within our biosphere.

Secondly, Luuk highlighted why circularity is considered important. Why does everyone go on about circularity? Because it’s meant to be sustainable. This is key. Circularity is the means, and sustainability is the end. We don’t have to use the metaphor of a circle. As long as human activity on planet earth becomes sustainable. That’s the goal. I have mentioned the metaphor of the spiral being a good way of looking at resource flows. Luuk somewhat echoed it, saying that ‘reduce-reuse-recycle’ should become ‘reduce-reuse-produce’.

Then Luuk went on to talk about more concrete examples. Few projects have actually integrated resource flows into their designs. However, the Autonomous University of Barcelona is looking into this.

He also mentioned energy. Energy efficiency and use depend on the timescale with which we look at a building. Being energy-neutral on the scale of a year doesn’t mean you have to be energy-neutral every day. Essentially, the term ‘energy-neutral’ as such doesn’t say everything. Compared to greenhouses, plant factories under artificial light (PFALs) are more energy efficient. The only difference is that greenhouses get their energy for free.

You can watch the webinar here.