My Experience on an Aquaponics Farm


This year, I wanted to get some hands-on experience with aquaponics. About a month ago, I spent three weeks working at Duurzame Kost, an indoor aquaponics farm in an old Philips factory in Eindhoven (Netherlands). In this post, I’d like to share some of the things I did and learned during those weeks.


Jos Hakkennes is the man behind Duurzame Kost. He has a background in livestock production, but also in getting disadvantaged people back into the job market. A few months ago, I got an email from him through this blog about meeting up.

For those who speak Dutch (or who are good at deciphering badly-translated YouTube subtitles), here’s Jos’s TEDx talk, where you can find out more. He talks about his background, the advantages of aquaponics, and his further plans. In 2015 Jos started a company called Blue Acres, with a greenhouse in Vortum Mullem. Later on, this expanded to Duurzame Kost.

For those who don’t speak Dutch – the name ‘Duurzame Kost’ has two meanings. ‘Duurzaam’ is Dutch for ’sustainable’. ‘Kost’ means ‘costs’, ‘wages’, and even ‘food’. In short, Duurzame Kost wants to make a living sustainably by growing sustainable food.

But Duurzame Kost is about more than food. It’s about helping less fortunate people facing difficulties in the job market to find meaningful work, acting as a stepping stone to being able to contribute to society productively. This gives the place a social role as well. The goal is to satisfy all forms of sustainability – ecological, economic, and social.

The rafts, seen from the harvesting area.

The System

Duurzame Kost produces rainbow trout and a variety of lettuce species and herbs. The trout are grown in conventional-looking tanks, about 3 metres in diameter. The plants were mainly grown on floating rafts in a deep-water-culture system, using blue and red LEDs. These rafts entered the system on one side, and slowly moved along to the other side, where harvesting took place.

There used to be a company called Wurmpie on the same floor growing mealworms, which used the waste from Duurzame Kost. Unfortunately, growing mealworms on such a small scale didn’t work for them.

(Anyhow, at Duurzame Kost, a lot of the waste (roots etc.) got taken home by people working at the farm. They would feed this waste to goats and horses. Who says an AMI-based ecosystem all has to be under one roof!)

The aquaponics system recirculated water most of the time, leading to fairly even nutrient concentrations throughout the entire system according to Jos. Now and then, the fish tanks were decoupled from the plants. This wasn’t done for nutrients, but for heat management. Why?

The optimal root temperature for leafy greens is around 18 ºC, but anywhere up to 23 ºC is still OK. For rainbow trout, however, 23 ºC is borderline lethal.

The surface area of the leafy greens’ water was far bigger than that of the fish tanks. To Jos’s regret, was no insulation between the water and the floor either. As a result, there was quite some heat being exchanged between the floor and the water below the rafts. This meant that the water below the rafts heated up far quicker than the fish tanks.

Because of this, the aquaponics system was occasionally decoupled to prevent the fish tanks from overheating. The fish tank water was left there to stay cold, whereas the plant water was allowed to warm up.

The transplanting area. Left: rafts for older plants. Middle: tables for transplanting. Right: rafts for young seedlings (with the fish tanks behind).

Speaking of keeping things cool: how was the farm affected by this year’s record-breaking heatwave in Western Europe?

It was boiling in there. Yes, indoor farms are less susceptible to the whims of the weather, but it still can have a huge effect. Many people would start at 6 AM to avoid the heat. Even then, we once got a wall temperature of 31 ºC — at 6 AM!

This heat was not only dangerous for the fish: it also meant the lettuce would start bolting, turning into bitter miniature palm trees. We also kept the LEDs on for less time, which made the purple lettuce less purple.

Even after the heatwave, it took a good week for the building to cool down to normal temperatures again. Jos is thinking about whether it would be worth using active heat pumps in the future.

Everyday jobs

Something I haven’t seen mentioned in discussions about aquaponics, except from practitioners I know, are the trivial but vital jobs that keep aquaponics systems going. At the end of the day, everything boils down to these jobs and the care put into them. Planning and conceptual understanding are useless if the people on the ground make mistakes.

The tasks I spent the most time doing were harvesting, removing bad leaves, washing, and packaging. After sorting, the leaves got washed three times in cold water, to keep them fresh and crispy. Afterwards, the leaves were put through a massive salad spinner, weighed, and packaged. This all was done first thing in the morning to get orders out the door on time. Speed was of the essence, but we had to bruise as few leaves as possible. Having the radio on really helped us stay focused.

Salad spinner at Duurzame Kost
One of the sizeable salad spinners used at Duurzame Kost.

After harvesting – and other jobs too – the area had to be cleaned. For the harvesting and packaging areas, this was done with an alcohol-based cleaning agent. Twice a week, these areas were cleaned more thoroughly, using a stronger cleaning agent. After this, the floor was dried using a water vacuum cleaner. Brilliant things they are.

The rafts also had to be cleaned. This happened in ‘showers’ made of old IBC tanks. The rafts were rinsed, scrubbed, sprayed with a peroxide/vinegar solution, and then rinsed again. Scrubbing can be seriously tough work.

The ‘showers’ where rafts were cleaned, made of old IBC tanks.

Another job inherent in aquaponics systems is the slaughtering of the fish. This doesn’t happen very often, but I was lucky enough to experience helping out once. The fish were caught with a net and then killed – using either a stun gun or with a whack on the head. Needless to say it wasn’t the most pleasant of jobs, but every aquaponics farm has to do this. The fish got cleaned afterwards and sold. All waste got stored in a freezer to be picked up later.

One of my favourite jobs was transplanting seedlings into larger rafts. This was done by putting the soil/coconut coir plugs into larger holes using what was referred to as a Pac-Man. This was quite different to the netpots filled with expanded clay I was used to at home.

Transplanting seedlings
Transplanting seedlings. From front to back: the new raft, a box full of Pac-Men, seedlings in their original raft.

Other jobs? One of the last ones I did was to remove cobwebs from the lighting fixtures. Just one of many things that had never crossed my mind!

Collecting data on ages and weights
Left: labels used to keep track of the crops’ ages. Right: form for filling in age, variety, and sellable and non-sellable weights.

Data Collection

Another thing I helped out with was the collection of data. At Duurzame Kost, they had already been logging the times taken for the plants to go from seed to harvest.

Jos also wanted to know how much yield came from one plant, and what proportion of that weight actually got sold rather than thrown away. One afternoon, Jos and I had a chat about how we could best do this. How would it fit within the existing tasks being done?

It sounds obvious, but there can only be data if people actually take measurements. If you’re working in the harvesting area, your main priority is to get orders out the door as quickly as possible – usually around 10 AM. A lot of people were concerned that weighing roots and leaves would be too time-consuming. We had to find a work-around that everyone was happy with. It was good to have had some hands-on experience doing these jobs, to be able to keep this in mind.

At AMI’s Farm Lab we talk a lot about collecting data in the abstract, but implementing it is another thing. Getting everyone on board is crucial.

The next thing I did was help Duurzame Kost get a system to visualise this data. As they say, if you are a hammer, you will see every problem as a nail. Having used Excel macros before, this was my natural choice. I made a system that gave an overview of the average age, weight, and sellable biomass proportion of each crop variety, by month. This had to take incomplete data points into account (e.g., keeping track of age was easy, but not every raft had weight measurements, since there wasn’t always time to measure every single head of lettuce).

Closing remarks

That’s about it from me. Thanks again to Jos for the opportunity. Be sure to check out Duurzame Kost’s website, and if you’re in the Eindhoven area, come and have a look upstairs on the 5th floor!

Leave a Reply

Your email address will not be published. Required fields are marked *