Aquaponics

Aquaponics is the integration of recirculating fish culture with hydroponic plant production. In fish-only recirculating aquaculture, nutrient-rich water is removed from the system and discharged to the environment on a regular basis to manage nutrient levels within the system. In aquaponics, this nutrient-rich water is seen as a commodity instead of a waste, and is used to grow plants. Once the plants have utilized the nutrients and cleaned them out of the water, the water is returned to the fish for further fish culture, and the perpetual cycle begins again.

The advantages of aquaponics are many, including:

• miserly water use - the water is used very efficiently to grow two crops - fish & plants

• zero environmental impact - no nutrient-rich waste-water discharge, the fish food is used to its maximum potential (to grow fish & plants)

• two crops from the one input - the fish feed entering the system supports the growth of both fish and plants

• small footprint/high density - because of their compact nature, facilities may be located very close to the end users (restaurants, green grocers, food manufacturers, public) in a variety of locations (country, city).

In addition, pesticides and herbicides cannot be used to treat the plants, as these would effect the fish, so the plant crops cannot contain any harmful chemical residues.

An awareness of Aquaponic technology is sweeping the world and there is a lot of information available from various resources. However, it must be remembered that Aquaponics needs to be adapted to local environmental conditions, and especially, to local native fish species (and especially their diets) , for it to be an efficient and viable technology.

An aquaponic system consists of a number of components. These include: the fish rearing component, the filtering component (both solids removal and biofiltration) and the plant rearing component.

Most aquaponic systems around the world rely on the use of the fish known as Tilapia. These fish are not allowed in some countries, as they present a significant environmental threat. Therefore, in these situations, we must rely upon native fish species. Tilapia are a very hardy species, with much wider oxygen, ammonia and dissolved solids tolerances than many other fish species, and because of this, require far less filtering and water quality control than many fish species.

The fish component of an aquaponic system is very similar to a standard recirculating aquaculture system. It comprises a fish rearing compartment (tanks), a solids removal filtering component and a biological filtering component. The biofiltering compartment is critical to aquaponic system design, because this contains the most important biological entity of the system: Bacteria. Whilst fish and plants provide the potential revenue or food sources grown in aquaponics, the bacteria are the work horses of the system. They allow harmful fish metabolite products to be converted to harmless waste nutrients that may be used by the plants. It is this bacterial conversion that is especially critical for aquaponic systems, as many fish species are relatively sensitive to these metabolic toxins. A good and efficient biofilter is an essential ingredient to successfully run aquaponic systems containing many fish species.  

There are a number of different approaches that may be taken towards the design of an aquaponic systems plant growth component. Probably the most often used system is to adopt gravel beds for the hydroponic component. This is a good method for small-scale, hobbyist or "backyard" systems, as the gravel bed may act as the biofilter of the system. In addition, if managed correctly, sometimes the gravel bed may also act as the solids filter. However, caution is required here, for if solids build-up and clog the gravel, it may lead to the establishment of "anaerobic" zones (zones containing no or very little oxygen) which harbour bacteria that can release toxins into the system. If solids are removed before the water reaches the gravel bed, these systems can operate very effectively.

For larger scale and commercial scale systems, hydroponic components are best designed with no media in mind. Popular hydroponic components are deep flow systems and NFT systems.

Deep flow systems are generally large tanks of water where the plants are grown in floating polystyrene boards that sit on the water surface. This allows the plant roots to grow directly into the water. Many commercial aquaponic systems use this method, as it is cheap to build, easy to manage and maintain and requires no or little media for the plants. The plants are placed into small, plastic net baskets that sit in wholes in the polystyrene boards. This allows the roots to gain access to the water and feed the plants the nutrients they require. This is the system most commonly used.

NFT (Nutrient Film Technique) is an hydroponic system consisting of many small "channels" into which the plants are again placed using net baskets. A thin film of water runs down the channel and allows the roots of the plants access to the nutrient. The theory is that about 90% of the channel area is actually air space, thus allowing the plant roots access to plenty of oxygen.

Whatever system is adopted, it cannot be denied that aquaponics is a fascinating food growing system. To date, it is recognised as the most water efficient food growing system in the world, and for a country like Australia, that can only be a good thing!