Aquaponics: the simple beauty of sustainable food production.

Aquaponics. When I first started working with an aquaponics system in 2006, most people would look at me cross-eyed when I told them what I was doing. And while I still get that look at times, aquaponics is moving from the obscure shadows to bask in the limelight…well, the limelight of foodies and sustainable farmers. But a limelight nonetheless. It is one solution to growing food in a closed-loop system, but by no means the only system. Aquaponics grows plants in a soil-less medium, using effluent from fish tanks to fertilize the plants. The plants, in turn, absorb the nutrients accumulating in the water, thereby cleaning the water for the fish. It’s a wonderful symbiotic system, where the plants and the fish benefit mutually. However, location is everything. Location determines your inputs (and the costs of your inputs) as well as where and for how much you can sell your plants and fish. The plants in an aquaponics system can be vegetables, fruit, ornamental flowers, or food for the fish itself (such as duckweed). The fish are all freshwater, and the most common fish grown in aquaponics systems are tilapia, perch, and barramundi, and some systems even incorporate other species such as freshwater shrimp or molluscs.

Looking over the conical settling tank. The baffles inside force the solids to settle to the bottom of the cone (which is buried underground).

The material inputs of an aquaponics system include the fish (at fingerling size), fish feed, seeds and substrate to germinate the seeds and support the roots of the plants, water, and energy to run the water pumps and air blowers. One could have all of your inputs from your own site if you can grow and process your own fish feed, breed your own tilapia, save your own seeds, and produce your own energy from solar or wind, but that is often not practical. A substantial amount of initial investment is needed to build the fish tanks, the hydroponic raceways, and the piping system to connect everything, as well as a filter for the solids and to help convert the nitrogen…but I’m getting ahead of myself. Fish eat food, and they – like all living creatures – produce waste, and that waste is primarily in the form of ammonia, NH3. Ammonia will break down over time (chemically speaking) and can be sped up in this process by nitrogen-converting bacteria, called Nitrosomonas, which help turn NH3 into NO2 – nitrite. Nitrobacter – another nitrogen-converting bacteria – helps to further break down the nitrogen into nitrate, or NO3. This is important for two reasons: one, nitrate is the form of nitrogen least toxic to the fish, and it also happens to be the form of nitrogen most easily absorbed by plants. So, it is essential for the nitrogen to have fully converted from ammonia to nitrate before it enters the plant raceways, or hydroponic tanks.

One of the simplicities of this seemingly complex process is that the water can flow from high to low, requiring the need of just one pump for an entire aquaponics system. The fish tanks are the highest, then the water flows into a settling tank, whose level is just a few inches below the level of the fish tanks. This settling tank impedes the flow of solid materials, such as leftover fish feed or fecal material. It gives it a chance to break down, and starts the process of converting ammonia into nitrite. Any sludgy material that sinks to the bottom will get drained out. This sludge is chock full of rich nutrients and should be composted and used as fertilizer on nearby gardens (hence the benefit of growing your own fish feed on site!) From the settling tank, the water flows into a biofilter. This biofilter can be a fancy manufactured piece of equipment such as mechanical sand or bead filters, or it can be a simple container where lots of inert material is placed and the water flows through slowly. This inert material is a place for the nitrogen-converting bacteria to live, and you need to strike a balance of keeping it clean and free of algae, and allowing the bacteria time and space to grow. From the biofilter, the fish water should then flow into an aeration tank where the water can be infused with air. The air in the water helps improve plant absorption, and that’s the next destination for the water: the hydroponic raceways. The plants’ roots in the water will absorb the nitrogen (in the form of nitrate), and the water leaving the raceways will have a much lower amount of nitrogen than it did leaving the fish tanks. The water gets collected in a sump, which is the lowest point of the whole aquaponics system, and where the sole water pump is located. The water is pumped back into the fish tanks, completing the cycle.

Shaded plant raceway with two types of lettuce.

The fish tanks and hydroponic raceways can be made from a variety of different materials, all with their own costs and benefits. Fiberglass is sturdy but expensive, plastic-lined tanks are cheaper but often less durable. Basically, one could make just about anything work, as long as they have the right fittings to create leak-free connections between each tank. This does involve quite a bit of PVC. Reliable energy is also crucial because without the air, the plants will quickly wilt and the fish will die. Monitoring the levels of dissolved oxygen (DO), the pH, and amount of ammonia and nitrite is important in the fish tanks, while it’s also crucial to keep tabs on the levels of nitrite, nitrate, iron, calcium, and other essential nutrients for plants. Many aquaponics farmers have found that they can grow a wide variety of plants without adding any supplemental nutrients just by ensuring a pH of 7.0, using high-quality fish feed, and having a healthy biofilter that allows for maximum conversion of nitrogen. Once established, an aquaponics system can be a very sustainable method of food production. The more inputs sourced locally, the more sustainable (and potentially cost-effective) the operation can be. Here in El Salvador, we are working on trying to create just that type of system to produce 100% organic fish and produce!

(End note: As of now, plants from an aquaponics system can never be labeled as “organic” by the USDA, according to their standards. The reason is that because the fish waste is being used to fertilize the plants, it is not composted according to the USDA’s very strict compost requirements. And if it’s not composted as such, it is considered raw manure, which may not be applied within 120 days of harvest in situations where the manure may touch (splash) the edible portion of the plant. So, since the plants are, according to the USDA’s National Organic Program, being fertilized with raw manure, they cannot be labeled as organic. But, if the fish are fed organic feed, and the plants are grown from organic seeds in an organic substrate and no chemicals are ever added, no pesticides or synthetic fertilizers used…it’s about as organic as you can get! It just can’t have the little green label, for now.)

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3 Comments Add yours

  1. We love your work.
    All the best from Croatia.

  2. This particular article, “Aquaponics: the simple beauty
    of sustainable food production. Locavore del Mundo” ended up being great.

    I’m generating out a clone to demonstrate to my associates.
    I appreciate it-Boyce

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