This idea came from the work that we do with sewage. Our systems produce a clean water effluent that is clean enough to discharge to ditches ponds etc. we wanted to develop a tertiary treatment system that would allow us to re-use the water for irrigation purposes. Hence the idea formed to create a hydroponic bog garden.
It essentially uses the same techniques employed in aquaculture. Use bacteria that are attached to biomedia to clean the highly oxygenated water passing through the media. We use alfagrog media for this. It has a high surface area and good void capacity. The added bonus to this system is that by placing a gravel bed over the top of the media we have been able to produce an ideal environment for growing those difficult to propagate plants. The moisture loving ones that fail at the first sign of drought.
You can find out more about us and our other projects on our site:Biotank
Step 1: Dig a Hole
The bog garden starts life as a square hole with a level base and square sides. The shape was determined by the sleepers that we are using around the outside in the finished bog garden.
Step 2: Line the Bottom
Once the base is levelled out, it is time to line the bottom of the bog garden with a cushion to stop stones rising up and making holes in the liner.
Step 3: Level the Bottom With Sand
First of all a sharp sand coating is added to level the bottom completely... Not that the digger driver was not able to get it completely level!
Step 4: Cushion the Bog
The lining cushion is laid out in sheets and comes right up the side of the bog garden. It has to protect the liner, which is 0.75mm butyl from harm. This is the same liner as would be used in a garden pond.
Step 5: Line the Bog
The liner is laid out and pushed all the way to the side of the hole. The liner is preformed to the size of the bog garden on purchase. It was made to measure for us.
Step 6: Add Second Cushion
Once the liner is in place it too is lined with cushion in order to protect it from the alfagrog that we will be putting on the top. The solid oak sleepers are put in the tank to separate off the aeration pond and the final settlement pond from the actual bog garden itself.
In the background you can see our experimental sewage system. This is a see-through Biotank 6 on which we do all of our experimentation.
Step 7: Separate Garden From Aeration Chamber
The oak sleepers, green untreated oak, have small holes routed in the bottom to allow the water to flow through into the bog garden from the aeration chamber. As with most things we where unsure how many were required so it is really guesswork!
Step 8: Add the Alfagrog
Having completed the basic design we fill the actual bog garden part with alfagrog. This is a ceramic filter media used in Koi fish ponds to filter the water. It contains a huge amount of surface area in which our bacteria will live and clean up the water.
Step 9: Add Water
Once we have completely filled the centre section of the hydroponic bog garden we then start filling it with water and adding the rest of the sleepers around the outside of the system. This size of tank takes around 6 cubic metres of water to fill it to a level just above the Alfagrog. Filling it with water allows us to level the Alfagrog and ensure that when we add the gravel to it that it is all immersed in water.
Step 10: Support the Center Section
The finished wood work looks like this. Full of water and Alfagrog and awaiting the gravel to fill the middle. The cross section wood is to stop the centre section moving when the gravel is added.
Step 11: Add Gravel
Once filled with gravel the finished bog garden looks like this. The water level is raised so that at least an inch of the gravel is under water to provide the plants with moisture. The whole purpose of this is not only to filter the water but to provide constant water for herbaceous water loving plants such as Hostas and Astibes.
Step 12: Get Ready to Aerate
The section of the tank that will receive the water from the Biotank needs to be aerated. A small compressor provides this aeration via a rubber aerator. The dissolved oxygen level needs to be as high as possible if the bacteria in the Alfagrog are going to survive.
Step 13: Put in Some Plants
Once finished the final touch is to add plants. All of these are moisture loving plants provided by our local nursery.