Urine infiltration : how to avoid over-fertilisation?

  • Geoffroy Germeau
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Urine infiltration : how to avoid over-fertilisation?

Dear all,


I hope my question will not seem out of the theme, and someone could reply

I Assume that a person produces about 2.8-3kg of N per year through urine, and plants require about 200 kgN/ha (*), the surface to irrigate would be about 150m² per person. This is context-specific, probably that a tree will consume more N, that in tropical climate where you can grow 3 crops per year.., the quantity of N produced is likely to be fewer, etc.
Ok could we say it needs at least 30m² ou even 10m² per person/student/dweler etc. How to find so much place?

-> Question : How to avoid over-fertilisation and groundwater pollution?

The problem/solution in term of nutrient seems to be in the urine. If there is not enough space to use such concentrated-readily-available-nutrients in such amount, the solution wouldn't it be to find a farmer who could use such rich fertilizer adequately?

-> Question :Or the fixation of nutrients in compost-toilet would be a good solution?
But in compost-toilet with big capacity the urine is either drained (contaminated urine infiltrated on a little area : pollution?) or evaporated (requiring energy and loosing the nutrients, at least N).
In the bucket-compost-toilet, as far as I know there is always liquid (urine) remaining on the bottom. Then The bucket is returned over a compost pile (about 1m³ for a family). Let's say there is no contamination under the compost (which I think should be discussed) : what to do with such a compost? How to avoir over-fertilization and then pollution?

Question : is there any ecological alternative to re-introduce it to crop-production by real farmers?

Thank you in advance for your comments,
and Sory for my so-poor english I hope I could be understood

Yours,

Geoffroy

I've been asked to introduce myself :
I'm bio-engineer, studied soil and water pollution issues, teached them in a belgian school, was trainee in niger and bukina in development sector, worked as wetland contractor/builder in belgium, closely intersted in ecosan/susan issues for several years, now working in wastewater and drinking water treatment sector, and a bit in biogas, and member of an group here in belgium aimed at promoting sustainable santation solutions (no fixed name yet).

(*)In the transposition of Nitrate-Directive, the max application in cultivated land is 250 kgN/ha and max 170kgN/ha if in a sensitive are in terme of N polllution.

Geoffroy Germeau
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  • mwink
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Re: Urine infiltration : how to avoid over-fertilisation?

Dear Geoffrey,

in our own research project, we fertilised with 3-4l of urine per m². This amounted to an N concentration of 69-92 kg N/ha. If I assume now that a German person excretes 1.2l of urine per day I need 110-146m² per person and year.
That's not a lot in agriculture but a lot (as you already mentioned) for private gardens or green areas around an office building.
To answer your first question: Yes, you need a farmer who takes the urine or you need a treatment system to get the nutrients out of the urine. E.g. P can be extracted by an struvite precipitation process and N via stripping. Then the question is: Is the fertiliser you produce still competitive on the market.
See e.g. this study: www.susana.org/lang-en/library?view=ccbk...p;type=2&id=1221

Regarding the addition of urine to compost, let me quote Hakan Jönsson, Prof. of the Agricultural University of Uppsala:

I discourage from using the urine in a compost, if you can use it in the field instead. A compost is hot, ventilated and has a fairly high pH, normally around 8. This means that a lot of the ammonia, normally more than 50% will be lost to the air, where it is a acidifying and eutrophying emission. Furthermore, you will need a lot of wood chips or straw.

Question two: I guess that alternatives will come up - extracting nutrients and using those within industrial processes. But till now, we haven't done this step besides some first lab-scale experiments. At least, I am not aware of such processes.

Yours, Martina.

Research unit Water infrastructure and risk analyses
Institute for Social-Ecological Research (ISOE)
Frankfurt, Germany

winker[AT]isoe.de
www.isoe.de
www.saniresch.de
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