The Future of Farming Is Powered by Fish Shit

I'm on a train headed to the end of the DLR line from London to visit a farm that grows salad leaves. But this isn't a trip to the countryside. My train terminates well within the M25, dropping me off at Beckton in the far reaches of East London. My map (I actually have a printed-out map) leads me to an ugly industrial park full of warehouses.

This unlikely spot is the home of GrowUp Urban Farms, the brainchild of former management consultant Kate Hofman and Tom Webster, who worked in business sustainability assessment. By bringing together an aquaculture system raising tilapia fish with a hydroponics system (a way of growing plants in water without soil), the pair are hoping to revolutionise farming.

Of course, urban farming is nothing new and plenty of other initiatives use sustainable closed systems that make effective use of small space. But what sets GrowUp apart is that the initiative is the first of its kind in the UK to bring these systems together on a commercial scale.

"Everything that's here is all existing technology. We're just integrating it and putting it indoors to create an aquaponics system from it," explains Hofman. "And you can easily transfer the concept and technology to any big urban area to be able to grow food that's in local demand."

The GrowUp warehouse is divided into two rooms. One holds twelve tanks with 400 fish in each (sounds a lot, but Hofman tells me this is very low density to the 3,000 litres of water in each tank) and the other contains floor-to-ceiling benches. Each row is growing three types of basil, micro-greens, and salad crops including watercress, kale, mixed salad, and pea shoots.

So how do the two rooms work together? Hofman explains that it's down to the constant re-circulation of the water, unlike a normal aquaculture system where the dirty fluid is flushed out.

"The water with the fish waste goes through several filters because we want the nutrients, not the solid waste for the plants," explains Hofman. "The real magic of the system is the bio-filter—basically, small pieces of plastic with a high surface area that colonise the bacteria which converts the ammonia in the fish waste into nitrates and nitrites."

Hofman continues: "The water is then pumped into the vertical ten-layer farm next door where the plants are growing. Each bench automatically floods in and out, calibrating how much water is needed for what's growing in that section. We grow leafy greens because that's what grows best with the waste from the fish and means we can minimise the amount of fertiliser we add in."

To complete the circle, the water which has been purified by the plants is pumped back into the fish tanks.

Hofam and Webster started GrowUp's commercial operations at the Beckton site in March, having previously trialled the system on a smaller scale from a shipping container in nearby Stratford. They aim to produce 20,000 kilos of salad a year, enough to feed around 3,000 people. Hofman admits it isn't much, but part of the GrowUp ethos is to keep things local.

Walking among the towering rows of green at the Beckton warehouse, catching just a whiff of the basil peering out from its bench above me, Hofman says: "We're growing things that have a quick turnaround (current crop varieties take between eight and 30 days to grow and harvest), and are delicate and perishable, so it makes sense to grow closer to consumers. They get a fresher product, meaning they last longer, and people waste less."

Sounds like a good deal to me.

Currently, GrowUp supply First Choice Produce (a distributor at New Covent Garden Market), restaurants like Rosa's Thai Cafe, and online delivery service FarmDrop. They're all based in London but Hofman hopes that aquaponics farming will spread across the UK.

"What we're doing here is all about big-scale production and showing that it's possible to use aquaponics in a commercial environment to grow food," she says.

Rolling hills and patchwork fields it ain't, but with population soaring and the agricultural industry still the biggest user of the planet's accessible freshwater, we need to start thinking outside the box about how we grow.

According to stats supplied by the British Leafy Salad Association (yep, it's a real thing), 346,968,000 bags of salad are sold every year and the leafy salads market as a whole is worth £635 million. It's big business in the UK, which currently still imports 50 percent of leafy salads products like lettuce.

Back in the aquaculture room hanging out with the fish, I ask Hofman what happens after five or six months when they're fully grown. Shouting above the noise of the magic bio-filter, Hofman tells me that at the moment, the fish are humanely killed by electric current on-site and given to friends. The plan is to make their system even more efficient.

"We're just waiting for local authority approval to sell the fish to local customers as well," explains Hofman. "Tilapia is the most commonly farmed fish across the world and has a nice, mild flavour but we just don't eat much of it here at the moment. It's also such a good protein for the amount you need to feed them."

Hypnotised by the white fish swimming around the tank, I notice the odd red one. Hofman laughs: "Yes, the guy who supplies us with the fish isn't always so great at separating out the red ones, but we'll be more stringent on that for consistency reasons when we're selling them."

Poor red tilapia. I'll take you home for my fish supper.

Talking to Hofman, it seems that the possibilities to evolve GrowUp are endless.

"Our vision for the business was that this would be our concept farm and eventually be used for research," she says. "We want to build farms that are five or ten times this size."

So, there may well be an industrial farm powered by fish poo coming to a town near you soon. You heard it here first.