Mark Laurence

Aquaponics - the first true closed cycle food system?

aquaponics

System by Joel Malcolm, Austrailia's originator of aquaponics

hydroponic greenhouse

A homemade aquaponic system (from Backyard Aquaponics Forum)

aquaponics

Homemade system by Janet Pelletier (USA)

Tilapia fish

Tilapia - a productive food source

In a recent article I talked about hydroponics as a highly productive system for producing food, especially for urban food production. Aquaponics takes this to the next level of production and becomes possibly the nearest thing to a closed loop food system - especially when used in an urban environment.

By closed loop system I mean cyclical, without external inputs. Currently, most (if not all) systems that man devises are linear, production-consumption-waste routes that rely heavily on fossil fuel for energy. In commercial agriculture, for every calorie of food energy produced, ten calories of fossil fuel energy are used. We desperately need food systems that give high yields for low input, and with low to zero transport costs - and that means urban food production.

Modern aquaculture is seen as a solution to producing high levels of protein, but it has a problem: for fish produce a lot of waste, which in conventional terms, is seen as pollution. A closed tank or pond aquaculture setup needs to change 10% of its water volume per day, which can add up to thousands of gallons. Hydroponics, meanwhile, requires external input in the form of nutrients, which have to be manufactured and processed somewhere else, and transported. When we realise that polluted water from fish, is simply nutrient-rich water, the same as we use in hydroponics, voila! One system's waste output becomes another system input, and we are a long way to closing the loop.

This is not, of course, a perfect system, for the like of such does not exist. It comes pretty close, however; the main external input being electricity for the pumps (which can be PV) and fish food. If the chosen fish are Tilapia, which are omnivorous (ie eat anything) then we can feed them with plants grown within the system, such as duckweed (Lemna). Whilst the fish might not grow quite as fast as if fed with high protein feeds, they will grow! Fish waste solids are siphoned off from the bottom of the pools and fed to worm compost systems (vermiculture), so worms can be used as protein feed and we get another spin-off - nutrient rich compost! Tilapia originate in the Nile and are a warm-water fish, so not suitable for outdoor systems in the UK. Compared to our cold-water fish, they are fast-growing, being harvestable in about eight months, as opposed to eighteen for trout.

the pictures shown here are from various systems, mostly Australian. They tend to be decidedly home-made looking, which is great for it shows that, as always, major innovations start with inspired individuals, and that everybody can do this. There are now an increasing number of commercial systems coming into use in Australia, the USA and elsewhere. See backyardaquaponics.com and autopot.com. As far as I know, the only people to try this in the UK are Herbs from Wales.

I see this as a potential urban food system, which is low input, high output, doesn't require soil, or access to soil and which could be built, or retrofitted onto most buildings. With this system, a large proportion of the building users' food could be produced - how much and how varied, depends on the users' ingenuity, minus whatever site restrictions apply. Every family with a balcony or basement (given artificial lighting) could have a system like this! In a community, swapping harvested produce fills the gaps in production (my fish aren't ready but yours are... let's do some barter!). Rooftop chickens might be another, balancing, system, giving, eggs, occasional meat and of course fertiliser to feed those plants you do grow in beds (root crops and brassicas, although even these can be grown hydroponically).

These systems have the potential to be integrated into landscape features, both inside and outside the building. Imagine skyscrapers, with atriums filled with waterfalls and landscaped ponds, with edible species of fish instead of koi. To the sides, on the building walls, rows of vegetables are growing, providing food for the building users, or the cafes and restaurants within. Some aquatic plants too can be harvested for their nutritional qualities (eg. watercress, water chestnuts) and again, can be designed into the scheme in an ornamental fashion.

This way of thinking about food, resources, waste and aesthetics is exactly what we need if we are to evolve into a higher species, with a lower - much lower - impact upon the planet.