Basis of Aquaponics

What is aquaponics?

Aquaponics is the combination of aquaculture (raising fish) and hydroponics (growing plants in water, without soil). The basic principle of aquaponics is very simple. Fish are grown in aquaculture tanks and nutrient-rich water from fish culture is pumped into hydroponic beds to irrigate and fertilize plants. After the plants absorb the nutrients, the purified water is returned to the aquaculture tank.

How do aquaponics work?

Fig. 1 Schematic diagram of an aquaponic system

In aquaculture tanks, fish consume protein-rich feed and excrete waste (mainly as ammonia). About 28-65 mg of ammonia nitrogen is released per gram of feed consumed by fish. Ammonia at high concentrations is actually toxic to fish and must be removed to promote healthy living conditions. This is carried out by naturally occurring microbes known as ammonia oxidizing bacteria (AOB), which convert the ammonia to nitrite (NO2-), and nitrite oxidizing bacteria (NOB), which convert nitrite to nitrate
(NO3-). Nitrate is the preferred nitrogen source for many plants. In aquaponics, the nitrate-rich water in the fish tank is pumped through a clarifier prior to the grow bed, where plants are grown hydroponically, that is in the soil-less system. The clarifier removes the majority of the suspended solids which may be detrimental to plant roots. There are a number of different design of hydroponic system, such as, nutrient film technique, flood and drain (also known as ebb and flow), and floating rafts. These designs are discussed in details in “Aquaponic design”. Figure 1 employs the floating raft hydroponic design. Once the plants absorb the nutrients present in the aquaculture effluent, they basically help to remove the pollutants (primarily nitrogen compounds). The cleaned water then flows back into the aquaculture tanks.

Why aquaponics?

Aquaponics has become increasingly popular in recent years. It is likely to be one of the widely accepted methods of food production in the future. Some of the advantages of aquaponics are:

  • Less water usage – it requires < 2% water than that used in traditional farming.

  • Minimal environmental impact - the water is recirculated in the system and no nutrient-rich wastewater is discharged into the environment.

  • Energy efficiency - two crops are produced from one input.

  • High quality product - nutritious and high-quality products (i.e., fish and plants) are produced without the use of pesticides or chemical additives.

  • Locally produced - aquaponics is located very close to the end users because of their compact design. This greatly reduces the costs of transportation, saves energy and reduces the environmental impact.

  • In addition, urban aquaponics provide job opportunities locally.