Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

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  • HAPitot
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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

I think we have to be clear that both N-P-K and urine fertilizers have to be seen as booster fertilizers which do nothing to improve soil quality. I have always advised the use of stored urine in combination with compost or the composted solids from UDDT toilets, and that is, of course, adding additional nutrients, phosphorus, in particular.

So, from that point of view, both mineral fertilizers and urine are similar; ideally, in the long run, both require the addition of soil amenders, and both result in mineralized soils if these soil amenders are not used. That is were human feces and other types of manure are coming in.

What I am recommending is a base fertilizer in the form of compost (where composted feces would be an ingredient), and the addition of diluted stored urine during the growing season. So, urine is applied as needed by the plants and directly where it is needed. In that way, it is working well, provided the soil quality is good.

These recommendations actually are along the lines of the principles of organic agriculture, trying to incorporate ecosan fertilizers into organic farming.

H-A
Hanns-Andre Pitot
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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

Happy to stand corrected, but my understanding is that urine is very high in nitrogen (can be over 10% in a high protein diet), low in phosphorus (1%), and moderate in potassium (2-3%). I've always understood that it is not a balanced fertiliser, especially where P is the growth limiting nutrient.

What I'm interested in is the nutrient levels of effluent that includes urine but where worms are digesting the solids and releasing liquid excreta. I'd expect a much more balanced liquid fertiliser than from urine alone.

Regarding dilution, this is actually a good thing because plants require dilution of urine. In my nursery I liquid feed with 100g urea per 200 l water with a good growth response. I don't want to waste the nutrients in a soakaway, but use the nutrient-rich water for irrigating crops.

cheers
Dean
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  • Elisabeth
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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

I was going to write the same as Hanns-André regarding Dean's statement about urine:

But what you are saying about phosphorous in the urine is not what I know: more than 60% of excreta phosphorous is supposed to be in the urine. So, stored urine is a fully fledged 'booster' fertilizer.


This is in reaction to Dean's statement:

If water is available at the latrine and in demand for irrigating crops, a complete NPK liquid fertiliser (effluent) would surely be preferable to urine (N+K), thus my angle being to provide nutrient rich effluent from the toilet system.


Urine is a complete fertiliser and rich in P. In fact, it is usually valued especially for the P content (as well as the K and the micronutrients; more so than for the N). Also when compared to a commercial liquid fertiliser, don't forget that those cost money whereas urine is in theory for free (although yes, you may have to transport it which incurs costs as it's more diluted than commercial fertiliser).

If someone wants to brush up on these fertiliser aspects, I recommend this post which gives you the Top-5 key documents in the area of excreta as a fertiliser:
forum.susana.org/forum/categories/17-fer...-production-of-crops

Regards,
Elisabeth

P.S.
Abbreviations used in this post:
N = nitrogen
P = phosphorus
K = potassium
Dr. Elisabeth von Muench
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  • Tore
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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

I don't want to loose any of the nutrient value in the urine so I don't want to dilute it or allow it to sock away. Since the urine holds most of the N,P,K I want to capture and use the urine for fertilizer. With the urine nutrients I can raise nutritious crops.

Tore
Sanitation & water consultant in developing countries

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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

Dean,

It's interesting to hear what you are saying about the resilience of these worms. I am using a backyard composter with worms (the European compost worm species, which is closely related to the American tiger worm species), and it is working a lot better with them than without. No more anaerobic zones where there used to be.

But what you are saying about phosphorous in the urine is not what I know: more than 60% of excreta phosphorous is supposed to be in the urine. So, stored urine is a fully fledged 'booster' fertilizer.

That doesn't mean you can neglect the feces. Apart from nutrients, the good thing about them is the organic content which helps build the soil.

H-A
Hanns-Andre Pitot
M.Eng. Environmental Pollution Control
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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

Hi Hanns-Andre,
I too am wanting to keep things simple and low cost.

The "gold standard" is a water seal to exclude odours from below. Urine diversion is not something I'd do by preference and therefore not something I'd offer others. I probably stand corrected, not having experience with it, but seems to me like twice as many receptacles to clean and keep odour-free and I dare not use water even for handwashing for fear of upsetting the drying. If water is available at the latrine and in demand for irrigating crops, a complete NPK liquid fertiliser (effluent) would surely be preferable to urine (N+K), thus my angle being to provide nutrient rich effluent from the toilet system. The issue then is pathogens. And conveyance to the crops.... simply and inexpensively.

What surprised me with wet composting, and what I did not believe until I practiced it, was that it is much easier than I thought to have aerobic decomposition even when air is excluded from a pile of wet feces and toilet paper. Seems like an oxymoron, but what actually happens is that the pile (if the urine is diluted with water and there is good drainage) will sit there without decomposition taking place. It doesn't stink because the urine has been diluted and drains away. If arthropods and annelids have access to it they "work" it from the outside in. There is no need for mechanical agitation. All that is required is conditions suitable for them. The only opportunities for a pile to grow are caused by cool seasonal conditions or the lag caused by more influent than the existing population can deal with. In either case a pile is a temporary situation until the balance is restored, thus a resilient system.

cheers
Dean
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Re: Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

Thanks everybody for your interesting inputs - I will be considering all of them. I agree with Tore when he is saying keep it simple, simple, simple. I think that and affordability are key.

And Dean, I think you have given a very good summary of the strategic issues associated with composting vs. dehydration. Of course, if you aim at resource/ nutrient recovery, the first thing to check is whether a market for the fertilizers would be available. In the case of that particular toilet in Adjumani, I can assure you it is located close to the plot of a farmer who has been taking whatever he could get his hands on (as long as the price was reasonable).

Keep in mind that in most poor regions of the world, the existence of artificial fertilizers is something theoretical, it's not a realistic alternative because of the costs. And animal manure is usually in short supply. If people are not inherently opposed to using processed human excreta as fertilizers, these fertilizers are becoming an interesting alternative.

And concerning urine diversion in composting toilets, I think there are more reasons to do it: It can help avoid anaerobic zones in the composting mass, especially where ventilation is poor. It can reduce the amount of carbon rich additives thus making the container required for composing smaller and less expensive. I will also very significantly simplify the treatment of the effluents. - Just some thoughts.

H-A
Hanns-Andre Pitot
M.Eng. Environmental Pollution Control
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Fertiliser qualities of excreta products from UDDTs compared to vermicompost digester

Note by moderator:
This post and the ones that follow were originally in this thread: forum.susana.org/forum/categories/70-com...it=12&start=12#16785
They have been moved to a new thread as they began discussing a new topic.

++++++++++

I think the discussion needs to be around the two key differences between the systems:
  1. One dehydrates, the other composts. Both produce biomass/nutrients suitable for fertiliser, but in a different way.
  2. One produces liquid effluent, the other has the advantage that it doesn't.
Hanns-Andre also described a hybrid system where he diverts urine, composts the solids but has additional water input into the compost and thus liquid effluent output. This liquid needs to be dealt with (e.g. soakaway). The simplicity described with the "pure" UDDT is that dehydration takes care of the solids and from what I've read can even dehydrate the urine .

Once you start adding water for handwashing and cleaning of the toilet bowl, or as the carrier of solids (e.g. for the convenience of a water seal or flush), this is now a wet compost, also producing liquid effluent. This effluent is contaminated with fecal pathogens and requires either secondary treatment to be used for irrigating plants, or can be drained into the soil immediately adjacent to the toilet and over time risks contaminating the water table. Furthermore, it seems to me that diverting the urine no longer achieves any purpose in a UDCT unless there is genuine demand for it within the community, because wet composting does not need urine diversion to be smell-free and aerobic.


cheers
Dean
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