aquaponics, Foto's, Ministry, Reizen

Aquaponics in Uganda

During last month’s visit to friends in East Uganda we helped them design and build an aquaponics system that both can provide much fresh produce for their family, as well as function as a demonstration and practice system for others to learn and improve for implementation in local contexts. We tried to use as many local resources as possible, but the pump and IBC tanks are still quite expensive and difficult to find. For that we are hoping to use other tanks and pumps in future models.

Since the land was sloping down we had to make mounds of dirt to allow the water to run back into the sump tank. In hindsight it may have been better to put the fish tanks (IBC tanks) and sump tank (black round tank) on the low end of the line of blue barrel grow beds, so we wouldn’t have had to move so much dirt. However, with all the help we got the job got done! Now our friends will finish and test the last parts soon and then the system can get cycled.

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Here’s a little overview video from our first test run:

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The system consists of two 1000 liter IBC fish tanks. These overflow through a Solids Lift Output into the 22 grow beds filled with gravel, which consist of 11 half 200 liter blue barrels. A simple stand pipe with a 11 cm diameter gravel guard provides the right water height. The water flows from the grow beds back into the 2000 liter sump tank, in which the pump is located. This 10.000 liter per hour pump (0.5 horse power/450 watt) at a head of 1.5 meter (so probably 8.000 liter or so at 2.0 meter) fills up the fish tanks in just over 10 minutes. This was the smallest capacity for any quality pump we could find, but it could be replaced with another smaller pump if that can be found, or else with a rope pump powered by hand or by a bicycle. (see here for a great one!)

Since the pump has more capacity than the SLO’s can handle the fish tanks start to overflow. For this purpose extra pipes have been added that lead excess water back into the sump tank, providing extra oxygen in the process. The pump will be on a timer to ensure flood and drain movement in the grow beds.

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The SLO design is based on this idea. It seemed to perform well in our trial runs (see pic on the right).

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All piping is 50 mm in diameter. For the outflow out of the fish tanks into the grow bed we need to replace the one 50 mm pipe where they come together with a 90 mm storm pipe to make the fish tanks drain better.

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The 11 barrels were previously used for white oil. We cut them in half, washed them twice, and then used a metal pipe heated in a charcoal stove to melt the thread of the hole in the top to glue in a PVC reducer from 2″ to 1 1/4″. For a next system we might consider putting the outlet in the lowest part of the barrel instead for better outflow and less work, but possibly a higher risk of leakage if the seal is not done well. The media guards were cut from 11 cm rainwater pipes.

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We tried local gravel to fill the grow beds, but after testing it in a cup of vinegar the bubbles showed that it contained limestone, which would affect the pH of the water. We therefore ordered a small truckload (4000 kg) of a granite type rock from a nearby town for about $100. Two guys spent two days sifting the gravel and then washing it out twice in a wheelbarrow before filling up the grow beds. We still have to fill up the space between the barrels more to keep them from sagging in the middle.

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And here is the result so far. The pipes that lead the water into the grow beds have been cut, but have yet to be put in place. Then all the piping needs to be tested and waterproofed where needed. As shown below, the system can be easily expanded in the length, or more rows of grow beds can be added. The two 1000 liter fish tanks should be able to support up to 50-60 grow beds if the system runs well.

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