Aquaponic Farming

What is Aquaponic Farming?

Aquaponics is a system that combines two established technologies, aquaculture and hydroponics, to create a symbiotic ecosystem. Aquaculture involves cultivating aquatic life like fish, shrimp, snails, crayfish, oysters, etc., for food, while hydroponics consists of growing plants without soil in sand, gravel, liquid or other media. Aquaponics is not a new concept. In ancient times, settlers in Mexico City built rafts, planted vegetables, and set them adrift on the lake to soak up the nutrient-rich water produced by fish and other organisms, and this was an early form of aquaponics.

INMED is concerned about adequate childhood nutrition, developed a low-cost, simplified form of aquaponics. This system is suitable for low-resource settings and uses locally available materials. Because these systems do not require physically demanding labour, they can be used by mothers near their homes or disabled farmers. Larger systems can also provide a sustainable source of income. INMED did not invent aquaponics, but they did develop a modular design that can be expanded incrementally as additional income allows.

Why Aquaponics?

INMED has modified the aquaponics technology to make it available to small-scale farmers and entrepreneurs in developing and emerging countries. The reason behind this is that aquaponics systems are much more productive than plots that are traditionally cultivated, and they also help preserve both the quantity and quality of water resources by not requiring chemical fertilisers or pesticides. Additionally, they utilise significantly less water than traditional irrigation techniques.

The benefits of aquaponics include the following:

Produces significantly more crops in the same space as traditional agriculture, creating much higher yields by comparison and producing fish as a second product.
Uses up to 90% less water than traditional farming methods, which is extremely water efficient.
Consumes much less energy than mechanised agriculture, requiring low electrical usage and no tractors/machines to operate, thereby mitigating emissions
Does not require mechanical or biological filters—the processes occur naturally, saving money and electricity, with fewer parts that can develop problems
Does not use harmful chemical fertilisers, pesticides, herbicides or fungicides, so produce is naturally grown and of very high quality and environmental conditions are not compromised by chemical production or waste
Produces its fertiliser from fish waste, reducing up-front capital
Requires substantially less labour than required by most other food production methods
Does not require soil, with fewer weeds to remove
Has faster produce growth to market size due to optimal conditions being maintained
Is vulnerable to fewer diseases (no soil-borne diseases) compared to traditional farming
Remains in constant production throughout the year and can produce out-of-season crops if the system is in a greenhouse
Promotes awareness of and strategies for mitigation and adaptation to climate change and natural resource conservation.

Aquaponics can accommodate the production of various fish species, including native river varieties. However, tilapia and catfish are the fish of choice, as they are hardy, fast-growing and widely consumed. Aquaponics also enables the cultivation of different plant crops, including fruits and vegetables.

Essential factors that argue for aquaponics include:

Affordable start-up costs, especially in relation to potential income generation
High gross profit margins (substantial commercial farmers can operate on lower margins)
Relatively low maintenance costs
Short-term and consistent cash flow
Local niche markets where small-scale farmers can enter, profit, and compete with large producers.

How It Works

There are three basic techniques used in aquaponics production:

1) an ebb and flow system, sometimes known as flood and drain, utilised by INMED South Africa

2) a raft or float system, also called deep water culture (DWC), and

3) nutrient film technique (NFT).

While the DWC and NFT systems are proven technologies, INMED South Africa employs the ebb and flow system specifically for the following reasons:

Simplicity in design, construction, implementation and operation, ease for beginners
Relatively low capital investment, using readily available local materials for construction
Grow beds that act as filtration systems, simplifying both construction and maintenance
No harmful chemical inputs
Low energy inputs (the single pump runs for only 15 minutes out of every hour)
Low ecological impact
Resilient against extreme weather conditions (made of a concrete structure)
Wider range of plants that can be grown without significant system modification1

INMED’s aquaponics systems consist of fish tanks, grow beds, water pipes, and a pump. They use a simple ebb-and-flow system that eliminates the need for expensive and complex filters and oxygenation systems. The entire system is built using common building materials. South Africa’s primary building material is concrete with rebar because concrete is durable and can withstand extreme weather conditions.

The figure below shows the pictorial representation of the water flow system of a single aquaponics module.

The systems can be designed to fit available space and meet production objectives, ranging from individual family-sized units to commercial systems of various sizes. They consist of fish tanks filled with water, grow beds filled with gravel and a small submersible pump that pumps water from the tank(s) to the grow beds through a PVC pipe. A timer is set to allow one water exchange per hour, which consists of approximately 15-minute flood periods followed by 45-minute drainage periods to the gravel-filled grow beds. As the water filters through the gravel, it deposits fish waste onto the surface of the gravel, where bacterial action converts it into nutrients that the plants can absorb. The filtered water then exits into troughs or pipes that return it to the fish tank(s). These systems can utilise solar and grid power and have a backup battery system to protect against power outages.

Using the Ebb and Flow System

The ebb and flow system comprises three primary components: the fish tank, grow beds, and pump.

The fish tank, made of rebar and concrete and buried underground, can be sized according to the system’s needs and is designed to hold fish. This tank is the heart of the system as it produces nutrient-rich water that contains essential nutrients, trace minerals, and oxygen required for plant growth.

The grow beds are made of concrete and rebar and are filled with small-sized 13-19mm gravel. This gravel acts as both a growth media aerator and a filter for the system. Plants or seeds are embedded in the gravel, naturally colonised by microorganisms. Nitrosomonas, one group of organisms, converts fish waste (ammonia) into nitrites, while the Nitrobacter, another group of organisms, converts nitrites into nitrates. The plants use these nitrates for growth and metabolism. This natural microbiological system eliminates the need for routine fertilisers typically used in traditional farming.

The figure below shows the pictorial representation of the symbiotic eco-system of the closed loop ebb and flow system.

The pump transfers nutrient-rich water from the bottom of the fish tank to the top of the grow beds. The water is aerated as it sprays from the nozzles and breaks against the gravel surface in the grow beds. The water deposits nutrients for plants to uptake as it flows downward through the gravel from gravity. The water takes up oxygen as it returns to the fish tank due to friction against the gravel’s surface area, which is necessary for the fish. It takes approximately 15 minutes to flood the beds, at which point the pump stops, and in approximately 45 minutes, the water drains back into the tank. Therefore, it’s called ebb and flow. Water returning from the grow beds is cleaned of nutrients that build up from the feed inputs. This closed system circulates on a continuous (24-hour) cycle.

If you’re interested in learning more about INMED’s fantastic work or want to know how you can help, don’t hesitate to contact them. They would be more than happy to answer any questions you might have and guide you on how to get involved.