Today we are visiting a group of sustainable growers who built an NFT (Nutrient Film Technique) Aquaponics system.
What is NFT Aquaponics?
NFT is actually very much used in hydroponics, it consist of growing plants and vegetables into pipes. The pipes are equipped with holes and the water and nutrients are running inside the pipes. Generally this type of system only hold a thin lay of water and nutrients, this is the reason why it is called Nutrient FILM technique.
NFT Aquaponics design
The trick in the design of those systems is to get the correct slope to get the water circulating into the pipes without being clogged by the roots and forming mini dams into the pipe. The usual slope goes between 2cm to 5cm per meter of pipe.
If you build your NFT system from classic pressure pipes I would highly recommend to leave the extremity of the pipe with a screwed cap that is both water proof and visitable. In this case if your plant roots grow very big and clog the pipe, you will be able to open the 2 extremities of the pipes and to use a long stick to push all roots out of the pipes. It will allow you to maintain the system clean and efficient.
Advantages and disadvantages of NFT:
NFT can be very interesting in terms of surface optimisation. It is often used flat (all pipes are displayed on a flat support) but it can also be used in the shape of a pyramid where the pipes are at different levels and therefore the height is used to increase the productivity per square meter.
Another advantage of this technique is that the cost per square meter can be very reasonable (depending on the type of channels/pipes used).
If designed correctly the NFT system will only hold a very low quantity of water and therefore the total weight of the pipe + water + plants will be very limited compared to a DWC or a classic growbed so if you want to grow food in a balcony, a terrace or any other surface where the load capacity is limited this is a good option!
The NFT pipe can be raised at any high, it makes things way easier when it comes to harvest the crop instead of having to bend to the floor and damage your back.
If you leave in a warm country where the sun can shine very strongly you should be careful with this technique as the temperature into the pipes can quickly raise and reach 50oC+ which is not good for the plants.
The Design of the system is a bit tricky in order to make sure ot get the adapted water level (not too high, not too low).
In NFT Aquaponics the level of water into the channel is very low. We must start with plants that will be able to reach the water present into the very bottom of the pipe.
Sensitive to water flow interruption
The NFT channels/pipes are placed on a light slope so if the water pump stops, the water into the pipes will be drained out. The plants will therefore remain without water and if the temperature is high the roots will dry and the plants will quickly die. While a DWC or classic growbed aquaponics system can handle days without water circulation (from a vegetal perspective), the NFT system can’t handle long power interruption. The water must constantly be running into the system.
What type of material?
In commercial NFT hydroponics the farms are equipped with channels specifically designed for this purpose. Most of the time the bottom of the channels are flat. This type of specialised channel is relatively expensive that is the reason why most of NFT Aquaponics growers are using either roof gutters or pressure pipe that are more affordable. The section of the channel/pipe generally goes from 100 to 160mm. I am sure you heard of the famous saying “the good size for the legs is when the feet touch the floor”. We can apply the same saying here, the good channel/pipe size is when the bottom of the pots placed in the pipe will touch the surface of the water.
NFT Water pump
In terms of water pump the NFT system doesn’t require a large water pump, a water flow of 50 to 150 litres per hour and per channel will generally be enough (depending on the pipe length). It is fair to say that those system are economical from a power perspective.
What type of plants for NFT Aquaponics?
As the plants are growing in a pipe, the volume available is limited. If the root system is larger than the pipe, it will clog the pipe and form “mini dams” into the pipe. The water level into the pipe can then increase and overflow out of the system through the pipe holes. For this reason we want to keep plants with a very limited root system such as strawberries, lettuce, spinach, herbs… and any other small leafy vegetables. Large fruits such as tomato will be kept in other types of system such as growbed aquaponics.
Analysis of Celine’s NFT system:
First I need want to congratulate the team as they built a descent size system without any previous experience in Aquaponics. They were able to grow fish and vegetables so from this perspective the mission is accomplish J Congratulations!!
Now there are always area of improvement and if I visited this setup it was also to give a constructive feedback on what could be changed to make the system more sustainable and efficient. Here are few of my findings:
In this video we can see a first swirl filter designed to trap the solids coming from the fish tank. Following this swirl filter we have a Bio-filter which is mainly composed of a drum filled with a variety of bacteria media. The aim of this biological filter is to offer a good support to the aerobic nitrifying bacteria biomass.
In this constant water level bio filter we can see that the oxygen supplied is very limited. There is little air pump present for this purpose but 6 air tubes are coming out of this pump and only one is used for the bio filter. Looking from the surface we can’t see any bubble coming so I imagine that most of the air is pushed to the fish tank which is shallower. The air pipe going into the bio-filter receives too much pressure from the water and therefore no air is supplied. A biological filter in constant water level needs a significant quantity of oxygen to work properly. I would highly recommend to increase the oxygen available into this drum.
From a design perspective I can’t see any easy way to clean the pipes in case of roots clogging. The vegetables such as tomatoes are producing well but may cause some clogging problems in the future. I would recommend to not plant such fruits into this system.
The water level into this system is very high and is regulated with evacuation valves. It is not conventional way to do it. It may work well because it is currently equipped with a very large water pump and therefore the constant arrival of oxygenated water maintain a correct level of oxygen around the vegetable roots. This system could be highly improved from a sustainable point of view if the water level was decreased and regulated with the pipes slop and not with valves.
The system is currently running with tilapia which is a very nice fish to grow in Aquaponics. The fish are kept in a nice tank but nobody is following the total fish biomass. The fish may have breed into the tank and therefore they don’t know how many fish are kept and what their weight is. There is a real risk of stocking a fish biomass higher than what the system can handle and losing all the stock.