Hydroponic farm +...

The photo at left shows a sub-tropical hydroponic farm growing bok choy in Brisbane, Australia using clip-together oval channel equipment under hail netting. It is the kind of food-from-the-roof technology likely to be adopted for Singapore rooftops - with the hail netting serving as a worker safety net, plus a barrier to rooftop debris flying away with wind gusts. An acre of this kind of hydroponics is more productive than six acres of good soil -- using less than a 10th of the water.*
* www.greenroofs.com/archives/gf_nov-dec05.htm

** More info on hydroponic farming is on: http://en.wikipedia.org/wiki/Hydroponic


----------
Here's something intersting I just came across, might be of some use later... It's called a FOLKEWALL. Further info is taken from wikipedia.
Inspired by Dr Gösta Nilsson's "Sanitas wall" at the Sanitas farm in Botswana, this technique makes an efficient use of space by fulfilling on its own two essential functions: a mutually beneficial system allies vertical plant growing and the purification of greywater.

Design

The basic design is a wall of hollow concrete slabs with compartments opening on one or both sides of the wall. The hollow parts are filled with inert material like gravel, LECA-pebbles, perlitevermiculite. In order to let the water trickle over the longest possible treatment path, plastic sheets are laid horizontally at intervals along the length of the wall between the pebbles. or

The water is brought at the top, and percolates following a zig-zag pattern throughout the inside of the wall. As it does so it feeds the plants which purify it in the same process. The plant rootsbeneficial bacteria grows over the pebbles, releasing the nutrients in the percolating organic material. At the bottom of the wall a container collects the purified water, which can then be used for non-drinking house uses or for watering the garden; or it can be returned to the top of the wall. grow through the inert material and extract nutrients from the water. A film of

Other considerations

Plants used: since the harvesting of the plants is a part of the purification process, fast growing, herbaceous crops are specially suited for the Folkewall. Perennials like trees and shrubs should be avoided.

Greywater: The water feeding the plants in the wall must be devoid of heavy and/or unsafe pollutants notably blackwater. This requires using source-separating toilets.

Pay-back period: Gus Nilsson calculated for his walls at Sanitas farm, Gabarone Botswana, that the growth and selling of tomatoes on the wall would pay the entire erection cost of the wall in three years.

Advantages

• Better use of the water: most of the evaporation happens through the plant's leaves, which makes the method specially useful in arid climates. It is this aspect Gus Nilsson makes use of.
• More efficient use of the area, for example in greenhouses or other glazed areas.
• In a greenhouse where the wall is used as a greywater purification device, it also works as a heat exchanger and -buffer.
• Purification of the percolating water, if greywater is used as irrigation.
• A wall x by x m2 is sufficient to purify greywater for 3 (or 4) people. The water can be reused in the house for non-drinking purposes, or to water the garden.
• In warm climates, the wall can be used as building material on the south side. This will cool the building.
• Low-cost housing: the combined use of Folkewalls and source-separating toilets would reduce the infrastructure cost by about 30%

Q/A with Dr. Folke Gunther from http://segate.sunet.se/cgi-bin/wa?A2=ind05&L=et-oden&P=1214:

First, I will tell you why I use the name 'folkewall' instead of 'living wall' as I used earlier. It is because I realised that this word already was in use for a sort of tombstones and in certain architectural constructions. Therefore I choosed the unique, although presumptious, word 'folkewall'

However:

"one of the advantages of 'vertical growing' that attracts me is the better utilisation of the growing area especially in greenhouses.
The example in Gus Nilsson, Gabarone, Botswana is therefore most fascinating"

"and is especially useful when you have a greenhouse that is constructed against the concrete wall of a building (http://www.iobbnet.org/drupal/node/view/313) or even in the middle of a east-west greenhouse.
Do you know of any such application in a greenhouse in Stockholm ?"

Although they have been discussed (on Ven in Öresund, also in large scale in Gotland, Sweden) none have been erected yet, to my knowledge. I planned to build one by myself the summer 2004, but circumstances came between.

"Do you have any data or can you say that productivity (product yield) per unit of greenhouse space is higher when a mixed ground and vertical cultivation are used ? ."

In a greenhouse, seveal walls will restrict light entrance, why you have to have them either in the middle or on one side. The other spaces have to be used for lower types of growing. The pcture above is for a planned greenhouse in Umeå (Farnorth Sweden). The beds are filled with horse manure to heat up the building as well as serving as a growing place (pictures of such a 'hotbed' at http://www.holon.se/folke/garden/vb/index.shtml , I will translate it)

Gus Nilsson calculated for his walls in Sanitas, Gabarone, Botswana, that the growth and selling of tomatoes on the wall would pay the entire erection cost of the wall in three years.

The interesting thing with the folkewall is that you combine growing with water purification in a mutually beneficial system

"Are there any crops that are specially suited for Folkewall ?"
fast growing, herbaceous. Perennials, like trees ans shrubs should be avoilded, since the harvesting of the plants is a part of the purification process"