In classical aeroponics, plant roots hang in the air and are periodically sprayed (or washed) with a nutrient solution. In the modern version of this agricultural technology, the roots are constantly immersed in nutrient fog.
Aeroponics is understood as the agricultural technique of growing plants without soil substrate. At the same time, the plant itself is supported by some supporting system, and its roots, freely hanging in the air, are irrigated with a nutrient solution. This is the main difference between aeroponics and hydroponics, which involves immersing the roots in a solution. The solution is supplied to the roots in the form of microdrops or aerosol (fog), depending on the spray device.
To prevent drying of the roots, the solution is supplied periodically over a period of time from a few seconds to several minutes. Such agricultural technology frees plants from soil diseases and pests, i.e. they grow healthier than the plants on the beds, but they have hypertrophied large and long roots, due to the rest of the plants.
Known principles for the construction of simple aeroponic installations
In the modern market of goods for amateur and vegetable growers, you can find any equipment for enthusiasts of agroponics. There are even single and multi-tier industrial aeroponic installations (such as "Harvest" installations). However, it is best for beginners in this business not to incur excessive costs, but using simple and inexpensive devices to create the simplest aeroponic installation for growing their first plants.
The simplest aeroponic installations are constructed according to the following three principles:
- Installation with a water pump.
- Installation with an air compressor.
- Ultrasonic installation.
The equipment for the first two types of installations is usually not specialized, but adapted - from a car and various household appliances.
Water Pump Installation
The layout of the installation device is as follows: the tank with the nutrient solution is equipped with a pump included in the cycle, which, creating the necessary pressure, delivers the solution through the hoses to the nozzle (spraying it and irrigating the roots of the plant. The plant itself holds a soft clip over the closed vessel (you can take a sheet of foam rubber) , and its roots are constantly suspended in the smallest drops of a nutrient solution.
Diaphragm or diaphragm pumps are best suited here. They can create pressure in the range of 2-70 atm, and also supply a solution from a tank installed much lower than themselves. It is possible for such a pump to supply pressure directly to a series of nozzles having a nozzle diameter of 0.4 mm and giving suspended particles with a diameter of up to 10 microns at the outlet.
Unfortunately, the vast majority of centrifugal aquarium pumps will not provide the required pressure even for nozzles having a nozzle diameter of more than 0.8 mm.
For such nozzles in the simplest aeroponic installations, it is better to take the washer feed pumps on the windshield or on the headlights. However, such a pump will certainly not pull more than one nozzle, just creating a stream of solution instead of an aerosol.
Installation with air compressor
In this scheme of the simplest aeroponic installation, an air layer with a pressure of up to 15 atm from the compressor is formed above the solution in the tank. Downstream from the tank, the tube for supplying the solution under pressure to the nozzle moves away. Having a nozzle diameter of 0.4 mm, the nozzle creates a suspension with a particle diameter of up to 10 microns.
If a pressure sensor is not integrated in the compressor, then it is installed at the top of the solution tank. There should also be a valve that provides emergency pressure relief.
The compressor can be an oil-free autocompressor with an auto shut-off function when the set pressure is reached, although it is a source of quite a lot of noise.
This type of installation cannot be equipped with aquarium compressors because of the low (less than 1 atm) pressure they provide.
The source of mist from the nutrient solution may be an ultrasonic emitter, for example, from a humidifier.
Its basis is a piezoceramic element in the form of a flat membrane, to which an alternating voltage is applied with a frequency equal to the resonant frequency of the membrane (about 1.7 MHz). As a result of the piezoelectric effect, the membrane begins to mechanically oscillate at the same frequency. if it is immersed in a nutrient solution, then in the layers adjacent to the membrane its regions of rarefaction and thickening of the fluid alternate with each other.
In the rarefaction areas, due to the cavitation phenomenon, the liquid boils without heating only by lowering its pressure, and individual small particles of liquid are ejected into the air. Fog from separate droplets appears above the membrane, the diameter of which directly depends on the frequency of oscillations of the membrane.
The temperature of the fog obtained in this way does not exceed 40 ° C, so it is called "cold". But this is still twice the optimal temperature in the root zone. If you try to cool the solution above the membrane, this will reduce the performance of the installation. The same will happen if the fog itself is cooled before it is fed into the basal zone - it will begin to condense. The imbalance in the thermal regime of the aerosol-fog restrains the use of ultrasound in aeroponics.
The second limiting drawback is the low salt content in the fog particles, which may be normal for seedlings and young plants, but for adult fruiting plants, at least twice as much salt concentration is needed.
If the membrane is immersed in the liquid by 25-30 mm, then its productivity is 0.3-0.5 l of nutrient solution converted to fog per hour. This is enough for a small number of plants.
During operation, the piezoelectric membrane is very hot, and the coating layer of the liquid cools it. To prevent overheating of the piezoelectric membranes, all such fog generators should be equipped with a protection against dry switching.
Piezomembranes of air humidifiers are characterized by the condensation of salts on them during downtime, which forces regular cleaning of their surfaces from salts. For the fog generators of aeroponic installations, there is no downtime for more than 20 minutes, therefore, salts do not precipitate on their membranes, and they do not need to be cleaned.
As you can see, the equipment for the simplest airborne installations can be equipped quite easily. To build such a installation is within the power of anyone at least a little familiar with technology. After that, it will be possible to experience first hand all the advantages (and disadvantages) of this modern agricultural technology.