Aquaponics projects
at my home, and
possibilities for your
city backyard, or the
eco-conscious office building.

Aquaponic projects at my home, and possibilities for your city backyard, or the eco-conscious office building.

When I started considering aquaponics in a Swedish climate, for efficient and space-saving food production in cities, my first question was – which fish species can we cultivate? Probably, there are several alternatives, but until I get more experience in fish farming, I have settled for one warm water species for greenhouse systems, and another for outdoor systems. In warm water, tilapia is a much used fish in aquaculture, that can adapt to different types of conditions. In permanent outdoor ponds, you can keep carp. Of course, you can also choose ornamental fish, if you are not interested in eating them, just in their fertilising effect. Or, for more advanced fish farmers, you can try trout, perch, or other fish.

In my home garden, I am about to construct two aquaponic projects.
The first one is a fairly straight forward greenhouse system. It will have an aquarium and a pump, pumping fish water to a storage barrel, placed higher. The barrel will have a regulated bottom valve, that opens to flush the growth beds. From the beds, water will drain of its own weight back into the aquarium. The growth beds will be filled with gravel, or maybe Leca clay balls for the roots to spread out in. Among the gravel, there will develop a bacterial community, which is essential for turning ammonia, that the fish excrete, into nitrate, and further into nitrite, that the plants can take up. It is also possible to grow duckweed, which is good, proteine-rich fish food, in one of the stages.

During winter, I keep the tilapia indoors, and give their water to my pot plants – and I have never had such beautifully thriving pot plants before! In this small scale system, I currently have ten little tilapia growing. I feed them leftover food and weeds! They happily eat bred crumbs, spaghetti and pancakes, and common chickweed from the greenhouse floor. In a more economically productive system, maybe the fish food needs to be more carefully balanced, but my fish are at least proving that they do not need fish flakes.

I haven’t had time to get carp yet, but I have a plan for an outdoor aquaponic system as well.

On a plot that is approximately 200 square metres, I plan to make vegetable beds, duck house and a water system. At the low end, there’s a fenced area for the ducks. They wander free in the rest of the garden, except the vegetable patch, but need a safe place for when they have ducklings, and they will love getting their own canal to swim in. The water will become a home for frogs and water insects, and that will provide the ducks with protein-rich food. Of course, duck manure will over fertilize the water. The water is therefore pumped to the long narrow canal that runs approcimately 15 metres alongside the vegetable patch. In my outdoor system, I will not have automatic irrigation of the vegetables, but instead dip a watering can into the canal when the plants need some. That way the vegetables always get a small dose of fertilizer in each watering. When the water level sinks, I will top it up from the well, but I will also connect the rain water drain pipe from the nearby roof, so rain water is harvested into the canal.

If this was in a backyard in the city, I would maybe construct soil-less growbeds instead of growing on the ground, and have the water automatically circulate between the canal and the growbeds. But my soil is so good, it would be a waste not to use it. Between the irrigation canal and the duck canal, I let the water deapen and widen into a pond for fish. The deapth will be at least 1½ metres, to ensure that carp will be able to survive winter there. The water will circulate continuously, and the mouthpiece where the water is pumped to the top of the system will be shaped to maximize aeration of the water.

When I have both fish and ducks constantly adding nutrients to the water with their excrements, I will have created a pond that people who know how to make ornamental garden ponds will shudder at the very thought of! That is because it will very likely become a green soup of algae in the summer. However – this can actually be a resource in this system! With a rake, I can easily fish out the algae and use as nutrient rich mulch for the vegetables! The filamentous algae that I hope to get are on top of that of a kind that can convert nitrogen from the air into a plant-available form, same as pea-plants can, and will indeed contribute to my vegetable harvest!

The system I plan to build at home is soil based. But in another context, this system could be converted to fertilise hydroponic plant beds, or probably easier plastic pipe-“beds” on walls, roofs or balconies. With or without ducks in the system, the fish can fertilise strawberries, lettuce, basil, tomatoes etcetera.

There is another interesting resourse in cities, that you can recover in food production, and that is wasted heat. On top of roofs there are often vents from the houses. I have myself seen how one of them always made spring arrive three weeks earlier next to the vent, than other places on the roof garden -even though it let its heat straight out in the wind. What if we could have placed a light-weight greenhouse there, to let a larger patch get the benefit of that heat. Done in the right way, we might be able to prolong the growing season a couple of months! If there is a lot of wasted heat to use, we could have heated aquariums, and grow giant shrimp! Those popular shrimp are often grown in mangrove swamps, that are destroyed by the shrimp farming. Wouldn’t an office with a glass façade be much more fun, if you, when looking closer, discovered that parts of the wall are a gigantic shrimp aquarium? Food for the shrimp could come from the restaurant inside, making a worm compost of its waste. In there, giant shrimp would be served with the freshest sallad you can imagine – grown a few yards further away. All of this is quite feasible, right now!

Some main thoughts are: look at your district – what wastes are there, and how could they instead be converted to resources? How can we build these parts together, so that we close the cycles, and do not have to waste transport energy in doing so? There is a lot to learn from nature, that we can use in the city. The result is sustainability plus beauty. Technical systems that are beautiful both in their smart strategy, and aesthetically!





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