Basics

In hydroponics and the associated aquaponics, there are different methods to supply the plants with nutrients. These can be divided into active and passive systems. Passive systems have the advantage of being independent of the power supply. Their efficiency is lower than that of active approaches.

Passive and Active Hydroponic Systems

Passive hydroponic systems are systems that function without a power supply. Active hydroponics uses pumps, aerators, humidifiers or spray nebulisers. These require electricity. Active hydroponic systems are more complex in design, but many times more effective in terms of plant growth due to the oxygen input. 

Overview

Schematic of an aquaponics system 

 A brief overview of the most common systems in aqua- and hydroponics

Passive Hydroponics: Wick Watering

The wick system (Wick Watering) does not require any moving parts or electricity. The plants are cultivated in a substrate that is supplied with the nutrient solution through the capillary action of the "wick". Supplying the plants via this system is not very effective. In addition, the wick can largely lose its nutrient transport properties due to mineral deposits. Another disadvantage is that no extra oxygen is supplied to the roots. The system is technically simple but plant growth is slower than with other active hydroponic systems.

Pros:

• cheap purchase
• without electricity
• without technology
• low nutrient consumption
• low control effort

Cons:

• very low yield
• slow growth

Active Hydroponics: Ebb and Flood Systems

Ebb and flood systems (Ebb and Flood or Flood and Drain) use pumps (4) that flood the plants with the nutrient solution in a time-controlled manner (2). The plants are embedded in a net pot. After the pump is turned off, the excess nutrient solution is returned to the reservoir (1) via an overflow (3). Often a residual amount is left to make the system less vulnerable in case the pumps should ever fail, enough water remains in the plant basin as the overflow ensures a minimum water supply.

By raising and lowering the liquid level (2), oxygen is introduced in the root area, which leads to more intensive plant growth. An electronic control system must adapt the ebb and flow rhythm to the requirements of the plants.

Pros:

• low nutrient consumption
• low water consumption
• high yield
• in case of power or pump failure: no crop loss

Cons:

• high purchase costs
• power supply necessary
• Control effort

Active Hydroponics: NFT - Nutrient Film Technic

NFT or Nutrient Film Technic (NFT) systems provide a permanent flow of nutrients that flow around the roots in a thin "film". A pump conveys the nutrient solution to an inclined plane on which the plant roots lie, thus providing them with a continuous supply. The constant flow prevents nutrient build-up.

NFT systems also add oxygen to the nutrient solution, for example through downpipes or intermeshing systems. The plant substrate is usually dispensed with, so that the roots have direct access to nutrients and oxygen and can thus grow quickly.

A disadvantage is the loss of all plants in case of defective pumps or power failure.

Pros:

• low nutrient consumption
• low water consumption
• very high yield

Cons:

• high purchase costs
• power supply necessary
• Control effort
• in case of power or pump failure: loss of harvest

Active Hydroponics: DWC - Deep Water Culture.

In deep water culture systems, also known as DWC systems, already rooted plants are placed in a net pot on a floating plate in the liquid reservoir, like a raft. To stabilise the plant, the net pot can be filled with substrate, such as clay balls. The roots hang directly in the nutrient solution, which is enriched with oxygen. This is done by means of an air pump and aeration stones that introduce very fine air bubbles into the water.

Since the roots are constantly supplied with oxygen-rich nutrient solution, the plants grow very quickly and vigorously. The system is simple and safe, even in the event of a power failure nothing will happen to the plants. Thanks to the large water reservoir, the system can be left alone for a few days without having to worry about it.

With the DWV system, the plants can also sit on a kind of raft and float on the nutrient solution.

Pros:

• low nutrient consumption
• low water consumption
• very high yield
• fast growth (oxygen)
• in case of power or pump failure: no crop loss

Cons:

• high purchase costs
• power supply necessary
• Control effort

Active Hydroponics: DFT - Deep Flow Technique (Deep Water Nutrient Film)

Active Hydroponics: DFT - Deep Water Nutrient Film Technique (Deep Flow Technique)
The Deep Flow Technique, better known as DFT, is a variation of the NFT technique, also known as the Nutrient Film Technique. Instead of the thin nutrient film, the plants are flowed around by a nutrient solution about 2-4 cm high. The principle procedure is the same and works recirculatory.

The deep flow technique DWT makes this cultivation system safer, because in case of pump failure the roots are still supplied. However, the method has hardly become established in the industry, because especially with longer / larger systems, the supply of oxygen to the plants varies and the plants grow unevenly as a result. It counts as one of the active hydroponics systems.

Pros:

• low nutrient consumption
• low water consumption
• very high yield

Cons:

• high purchase costs
• power supply necessary
• Control effort
• in case of power or pump failure: loss of harvest

Active hydroponics: drip irrigation

With drip irrigation (drip system), the nutrient solution is dripped onto the substrate around the plants via a drip line. The nutrient solution flows past the roots and supplies them directly. The excess liquid flows off, supplying oxygen to the root area.

Non-recovery system:
In industrial cultivation there are non-recovery systems to achieve a high yield without measuring technology. Here, the plants are always supplied with fresh and equally adjusted nutrient solution. The nutrient is not returned to the cycle to avoid the spread of pathogens. This method uses more water and unused nutrients are lost. This system does not require control of nutrients but relies on experience with nutrient use. One can run the system "blind".

Pros:

• very high yield
• fast growth
• in case of power or pump failure: no crop loss
• little control effort

Cons:

• high purchase costs
• power supply necessary
• high nutrient consumption
• High water consumption
   

Recirculating system:
The nutrient solution is fed back into the system, which means that only the nutrients that the plant actually needs are consumed. The flow rate is adjusted to the needs of the plants. Due to the closed system, however, it is necessary to control the nutrients in order to adjust them to the growth phase-dependent consumption. This system needs a regular control of the nutrient concentration.

Pros:

• very high yield
• fast growth
• in case of power or pump failure: no crop loss

Cons:

• high initial costs
• power supply necessary
• Control effort

Ohne Kreislauf

Mit geschlossenem Kreislauf

Active hydroponics: Aeroponics - fog of nutrient solution

In an aeroponic growing system, the roots of cuttings or plants are not suspended in a liquid but in a mist of nutrient solution. The plants are hung with net pots in a chamber where the roots are sprayed or fogged with nutrient solution through water nozzles / fog nozzles.

Aeroponic systems offer the optimal supply of the roots with everything they need to grow, they work very effectively and deliver maximum plant growth and therefore belong to the active hydroponic systems. However, the technical effort is high because of the high water pressure for the nozzles or the nebulisers used. In addition, technical measures must be taken to prevent the nozzles from clogging. A disadvantage is that a failure of the nebulisers is not tolerated by the free-hanging roots for a long time.

Pros:

• very high yield
• fast growth

Cons:

• high purchase costs
• power supply necessary
• high nutrient consumption
• high water consumption
• Control effort

Active hydroponics: aquaponics - plant cultivation and fish farming

Aquaponics (aquaponic) is made up of aquaculture (fish farming) and hydroponics (plant farming), so two farming systems are combined. The excreta of the fish are used to supply the plants with nutrients, they are recycled and serve as fertiliser.

The excreta are converted into nutrients that can be used by plants with the help of microorganisms. At the same time, the water is cleaned so that it can be returned to the fish tank and the fish have good living conditions. This creates a win-win cycle. In addition to growing lettuce and vegetables, fish are bred for food or ponds are kept clean with ornamental fish.

Fish farming can be combined with all systems that allow separation and control of nutrients through a circuit.

Active hydroponics: aquaponics - sump tank (CHOP: Constant high, one pump)

The decisive advantage of introducing a sump tank is that the height of the water level - especially in the fish tank - always remains constant. Only when water enters the fish tank from above through the pump does water flow back through the overflow. On the one hand, this means less stress for the fish and, on the other hand, the tank is filled with water even if the system fails (e.g. due to a burst pipe), as the water level can never drop below the overflow.