With aquaponics, sustainable urban farming reaches new heights of sophistication. As a module in the design of new cities it becomes increasingly attractive when it is realized that with aquaponics, the sustainable new cities would not need to import nearly so much material in order to feed themselves. Aquaponics, properly designed and managed, allows whole residential and commercial building complexes to recycle their organic waste within the building back into clean, safe food. Very large quantities of food can be grown this way on very small areas. No soil whatsoever is needed. The crops grow in fish farm waste water.
Of course there are intermediate organic conversion modules that separate the human waste and food waste from the human food chain for practical and hygienic reasons. Various composting methods can be used to bring human and food waste to very high temperatures for long periods of time. This eliminates the risk of human pathogens being passed on to the aquaponic urban farm stage of the recycling process. Sustainable urban farming does not have to be toxic urban farming! Aquaponic farming should be carefully managed to exclude human pathogens, which can easily contaminate the water if you are careless or inattentive.
Composting can also be used to breed insects as fish food. The main input for aquaponic farming is fish food, so it is essential to source this from sustainable sources, which are also cheaper than buying in food, when it can be grown actually in the aquaponic farming enterprise itself. Aquaponics is the marriage of intensive aquaculture (fish rearing) and intensive hydroponic vegetable and fruit cultivation, in a recirculating aquaculture process that uses a tiny proportion of the water normally required for agriculture. It is practical to re-use vegetable offcuts and insect larvae grown in various composting processes for fish feed, so that no fish food has to be bought in from outside. This also divorces the fish rearing industry in the city from dependence on commercial fish feeds using increasingly scarce and expensive ocean fish as a base.
However, in a new build city design, composting areas tied into the waste disposal system would have to be part of the integrated sustainable city design.
Methane gas is also a desirable and useful by-product of composting that can be compressed from the waste digesters and used for cooking gas, for instance. It can also be used to run boilers for steam for dynamos to produce electricity for city use.
To go back to the fish feed issue, basically insects such as soldier fly larvae have proven easy to harvest (they can be bred in a waste composting design that takes advantage of their tendency to crawl on their own into the hoppers provided) , and very nutritious and acceptable to fish such as tilapia.
Aquaponic urban farming systems could easily be established all over the flat rooftops of any city design, as long as the load bearing properties of the underlying buildings were beefed up to bear the weight of the water tanks necessary.
Aquaponic urban farms on rooftops could also double as amenities, with their own cafes and restaurants serving fresh food out of the integrated aquaponic systems designed to be aesthetically pleasing as well as efficient mass food production areas.
Flowers and fruit can also be grown aquaponically, and plants such as grain amaranth, for instance, grow excellently in aquaponic systems and provide a high protein grain that requires no further processing after harvest apart from drying, as well as ornamental flowers and edible leafy greens. An inspired designer could design local rooftop parks which as well as being pleasant to use, were also aquaponic farming areas of ornamental and economic value. It is simply a matter of siting the fish tanks and aquaponic tanks and the requisite pumps and plumbing imaginatively and ergonomically. In colder climates, greenhouse structures can be integrated with the building design in the first place to include malls, leisure areas, and so on into the design.
Banana plants and papaya trees will grow in growing media based aquaponic troughs, as part of a permaculture section of the rooftop or back lot aquaponic farm.
Since you need no soil at all for aquaponics, designs for sustainable new cities based on floating structures could also house aquaponic farm parks for their populations, recycling waste back to food and drawing the little water they need from desalination plants powered by the sun, or by methane driven electric power plants from the recycling of that same organic waste matter.
This technology has the potential to revolutionize how new cities are designed and run in order to be sustainable.
To find out more about how aquaponic farming can be built in to sustainable new cities and to understand this technology better, I highly recommend reading the following aquaponics textbooks to get a more expert viewpoint on aquaponics:
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