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Aquaponics Technology for Urban Food Availability

The magnitude of the impact of global climate change causing food supply strategies that relied on the central food producers is absolutely necessary to be changed. One of strategies to support these changes is through the utilization of the front and back yard as source of family foods. Nevertheless, agricultural cultivation in the garden, especially in urban areas, have distinct characteristics, which is it only has narrow even very narrow area. Therefore, optimization of the utilization of the yard in the term of cultivation of crops and food sources in urban areas are needed.

One of the optimization strategies is the use of the yard through the cultivation system, combined with fish farming called "aquaponics". Aquaponics is a sustainable food production system that combines a traditional aquaculture (raising aquatic animals such as lobsters, fish, or shrimp in a tub or pool) with hydroponics (cultivating plants in water) in a symbiotic environment. In this system, the same land area will be able to produce the two commodities simultaneously, ie, vegetables and fish. Cultivation of vegetables will directly supported by the underlying system (fish) which produces residual feed and feces that contain high concentrations of nutrients that can be utilized by plants as fertilizer. Meanwhile, media plants and root of plants will filter the water and maintain the water quality. This condition causes the pond water quality will remain good and free from residual feed and fish feces, and so it would be a good fish growth medium.

Although composed of two parts, aquaponics system consists of several components or sub-systems that are responsible for the removal of solid waste, supplier base to neutralize acidity, and water or oxygen regulator. These components include of (1) fish tank or pond, (2) catcher and separation of solid waste units, (3) biofilter, where nitrifying bacteria can grow and convert ammonia into nitrate, (4) hydroponics subsystem, which is part of the system in which plants grow and absorb excess of nutrients from the water, (5) Sump: the lowest point in the system where water flows to and from being pumped back to the rearing tanks. Removing solids waste units, biofiltration, and / or the hydroponics subsystem may be combined into one unit or one subsystem, which prevents water from flowing directly from the aquaculture (tank or ponds) to hydroponic subsystem. The biofilter unit has very vital roles since it relates to the process of nitrification.

Nitrification as a process to alter ammonia into nitrate in aerobic atmosphere, is one of the most important factors in an aquaponics system. Nitrification process can reduce the toxicity of water and as well resulting nitrate compounds so it can be uses as nutrient sources for the plantations. As one of metabolism products, ammonia continues to be released into the water through the gills and fish feces. Ammonia is toxic to fish (0.5-1 ppm) that must be filtered out of the system. Ammonia can be converted into other nitrogen compounds through healthy populations of Nitrosomonas (bacteria that convert ammonia to nitrite), and Nitrobacter (bacteria that convert nitrite to nitrate). In an aquaponics system, the plant roots become a place for those bacteria to growth. Once the system is stable, ammonia levels in the water ranged from 0.25 to 2.0 ppm, nitrite levels ranged from 0.25 to 1 ppm, and nitrates range 2-150 ppm.

In other words, plantations which growing in hydroponic subsystem, with roots submerged in nutrient-rich water from the sewage pond, will help to filter out ammonia which is toxic to aquatic animals. After passing through the hydroponic subsystem, the water becomes clean and rich in oxygen, and can go back into the water system.
Some green leafy vegetables known can grow well in a hydroponic subsystem are chinese cabbage, lettuce, basil, tomatoes, okra, melons and peppers. In addition, other species such as beans, peas, cabbage, taro, strawberries, melons, onions, radishes, turnips, sweet potatoes and spices can also be a selection of plants that can be grown in aquaponics. While freshwater fish species such as tilapia, catfish and eel are most commonly used in aquaponics systems.

So it is clear, aquaponics system is one of the best alternative technologies to be developed especially in urban areas to support optimization of the utilization of the yard. Aquaponics technology can be a first step toward self-sufficient family foods.