Edible wall

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This page is under construction!


See main actors

Objectives and context

Motivation: upgrading a multi-functional “living wall”

Our general motivation is to produce food on-site, while valorising excreta (human waste) and combining several advantages. In this project, our mission is to upgrade existing “living walls” to combine several functions and characteristics:

  • Grow edible plants (or medicinal, scented… instead of just decorative exotic plants)
  • Fertilise the plants with human source-separated urine only (and avoid using any chemical fertiliser)
  • Purify indoor air, which passes through the soil and root system
  • Use material that is renewable, locally available, … (as much as possible)
  • Have a beautiful planted wall, that increases well-being in offices, inside buildings, or in the city

Among these functions, we want to focus in priority on valorising human urine to grow edible plants. Yerk?! Yes, you read it correctly. And you should get convinced of the many advantages of the reuse of urine for agriculture by reading a coming page…

System description and constraints

Soil substitute
The vertical “modules” consists of panels of a kind of compressed roock wool: Grodan (although we might change this in the future if we find another renewable material with the same properties). The plants are planted in holes, and their roots then develop through this 'matrix' and at the back of the panels. Specificity: very little real natural soil, lightweight.

Fertigation (= irrigation + fertilisation)
Drip irrigation, with a nutritive solution made of tap water and currently a chemical fertiliser, which we’ll replace by urine. Similarly to a hydroponic system, the solution must contain all nutrients needed by the plants, in a readily available form, and in the appropriate concentration for continuous fertigation (as opposed to punctual fertilisation).
This means that the nutrients concentration shouldn’t be too high, because 1. Too high an ammonium concentration is toxic to plant [refs] 2. Excessive fertilisation also causes damages, such as nitrates accumulating in leaves [refs].

Plants for vertical indoor garden

Specific objectives

Challenge for urine fertigation in a semi-hydroponic system

Obviously we want to avoid odours, especially because this version of living walls is designed for inside buildings. But we also need to find the ideal urine dilution also to avoid excessive nutrients (see just above) and the toxicity of ammonium.

What's more, most plants prefer nitrate-nitrogen to ammonia-nitrogen as a nitrogen source, and these plants are easily damaged by excessive ammonium nutrition. (Shinohara et al, 2008) [enter ref] This is why most hydroponic solutions contain nitrates, not ammonium [ref needed]. However stored urine contains nitrogen in the form of ammonium, which must therefore be converted to nitrate. This requires the presence of nitrifying bacteria, and sufficient oxygenation. It is generally the case in soil… but how about in our living walls, in soil substitue? Is it a suitable medium to host active nitryfiers? For this reason, we first want to test the 'nitrification in modules'.

Questions for experiments

  1. Nitrification in modules - Does nitrification of urine take place in our soil substitutes? Is it quick enough? How it it influenced by the following factors?
    1. Inoculation (none / with nitrifying solution)
    2. Dilution factor (between 1:10-1:50)
    3. aeration properties of the panels (free surface / covered with a plastic sheet / active aeration)?
    4. Different soils, i.e. different source of microorganisms (none? / special for germination, sterilised / garden compost / field, without chemicals? / inocculated with an nitrifying culture)
  2. What is the ideal dilution rate?
    1. Limit to prevent odours
    2. Appropriate dilution to reach at least the same performance as the chemical solution (or compare between dilutions) – in these modules
  3. How do different edible plants grow under these conditions? Which are the most adapted?
    1. First selection: common herbs that grow well
    2. More interesting other plants: 2nd run, or first just in pots vertically – pre-test the dilutions
Could we start this last point in parallel during the nitrification experiments, or if it takes very long to build the structure, or in collaboration with Vertikal Farms ? (TBD)

People involved

Main actors: Alexandra & Michka M (easy to find on Slack or by e-mail)

Participants (have helped us so far):

  • at Hackuarium: Clément D., … and of course Yann H. & Yann P.
  • colleagues at ESTEE: Saida N., Théodore B., Tomas R.

External partners: We cooperate with the enterprises Biotecture and Living Green City UK. They produce and install living walls inside and outside buildings. Biotecture have provided us with the core of the modules and share some know-how. The team at Living Green City UK, in London, currently focus on air filtration function. We are in contact with them especially to ensure the integration of the different functions.

Friends and related projects: Vertical / urban farming, aquapony, and such species: Vertikal farms, Exodes Urbains, others met

Communication: Slack channel: #wg-edible-wall


Overview of project parts

Details on these activities will be found in the following sections (title level 2).

  • Urine Fertigation
    • Urine collection and storage – install DIY waterless urinal
    • Nitrifiying solution – design and grow a community of nitrifying bacteria
    • Wall structure and irrigation system – design & build
    • Test the nitrification in modules
      • experiment NM1 - with initial inoculation
      • experiment NM2 - with inoculation through different soils
    • Dilution test: planted experiment 1
    • Dilution test: planted experiment 2
  • Vegetal Community
    • Nursery: design, build and plant
    • Selection guide for different conditions (such as indoor/outdoor, light, space, etc.)
      • Select and gather plants for the first experiments
      • Matrix for indoor walls
  • Integration of air filtration
    • This will come later. Idea taken into account in the part “nitrification in modules”


Mhh, why is this empty? Maybe because we’re soo quick that we rise through time…


13.07.15 I've received the empty modules, to be planted!

22.07.15 openHackuarium vol.55 small presentation of project plans

Urine collection & storage

See the page DIY waterless urinals (This may serve also to other projects!)  

Nitrifiying culture

We'll create a page with more details when we see the first results!

Quick reminder of objective

Grow a culture of nitrifying bacteria adapted to diluted urine. It can then serve in 1° for us to:

  • Inocculate our modules with the suitable microorganisms, if needed

But also to:

  • Start an aquaponic system (with fish etc)
  • Stabilise diluted urine, with the effect of removing pathogens and smell => home fertiliser that's better than simple urine

Inspiration / background

We got inspiration from this

They want to keep the ammonium conc very low, good for fish. Target 2-4 ppm, increased by 0.5ppm daily. But in our case, we want a culture adapted to much higher concentrations; at least those used for fertigation. Try to go faster?

... more to come

Wall structure and irrigation system

Test the nitrification in modules – experiment

Dilution test: planted experiment