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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

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

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

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

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

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

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

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

The N-P-K values in urine can vary greatly depending on the diet. as an example the nutrient value for vegetarians is higher than meat eaters. The caloric intake will vary the nutrients in urine and the more water you drink the more you dilute the urine. The deeper the yellow, more nutrients. The average person will urinate about 1.2 kg of urine per year. In that urine will be 3.5kg N, .4 kg P, and 1 kg K. Different studies show different amounts so I am sure there will be different numbers posted.
The urine will have only minor affect on micro nutrients. Healthy micro nutrients comes from healthy soil. This is achieved by using the human fertilizer tilled into the soil. Commercial fertilizers kill the micro nutrients. Thought the feces is not as rich in nutrients it does contain about 10% of the N and K as well as 50% of the P. The feces (human fertilizer) also acts as a soil conditioner resulting in high humus, works, moisture retention, and micro organisms that produce micro-nutrients.
A person produces almost as much human fertilizer as is required to grow the food that will sustain him. This is one of the reasons that I am so positive on the UDDT.

Than main factors that influence nutrient levels in urine are:

1. Levels of protein in the diet (doesn't matter whether vegetable or meat). A high protein diet results in high levels of N.
2. Amount of water consumed by the individual. This affects dilution of nutrients in the urine (absolute levels), but does not affect the balance of nutrients (relative levels).

Fact is that urine is not a balanced fertiliser. What I am trying to raise is that vermicomposting adds nutrients to the liquid effluent. By drying feces, UDDT systems make "active" biomass (a good carbon and nutrient source once decomposed), plus urine. There is a disconnect because urine is not a balanced fertiliser. In contrast, vermicomposting digesters should produce a NPK-balanced nutrient-rich effluent. The issue I have is that this has apparently not yet been quantified by published research.

What I am trying to explain is that a vermicomposting digester produces "stabilised" humus (a good soil amendment rich in carbon) that apparently has low levels of pathogens (again not quantified) and the bulk of fecal material is reduced to liquid which combines with urine to be a nutrient-balanced liquid fertiliser (with variable pathogen levels depending on what happens next). There are two options for the liquid, secondary treatment and surface drippers, or simply discharging directly to underground soakage trenches that feed suitable food crops like bananas that respond to water + balanced nutrients.

By recycling balanced nutrients to crops, the risk of growth-limiting factors (especially lack of P) is reduced. One thing that needs to be clear is that by increasing productivity of land using liquid only ('booster'), organic matter (biomass or 'soil amender') levels are increased and so improve soil quality by being returned to the soil. Production of biomass is mostly limited by two factors, availability of water, and nutrient shortage. Abundance of some nutrients and shortage of others is no better than shortage of all nutrients.

cheers
Dean

muench wrote:
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).

I'm sorry but this is quite wrong and misleading, Elizabeth.

Plants require the correct amounts of various macronutrients (that's the NPK that we're discussing above) as well as a range of micronutrients to grow properly. Mostly they get these supplied to them from the soil. When the soil does not have enough of one or more of the nutrients, the plants will not grow very well.

Urine is a good source of urea, which is a good source of nitrogen. However, it is in no sense a "complete" fertiliser as it does not have equivalent levels of P and K, never mind the micronutrients.

But even if it did that's irrelevant as different plants in different soils need different amounts of NPK. In some situations the soil already has high levels of N, so adding more in urine is going to make no difference at all.

This idea that one can add anything to a farmed field and this will magically be what the soil and plant need is quite wrong.

Yes, I know that some here have had good results with their urine irrigation schemes, but these must be unusual situations and should not be seen to apply to everyone else in all situations. That's clearly not the case, otherwise there would be no need to have agronomists and soil scientists advising farmers on the correct amounts of fertiliser to use on their crops.

I agree with Dean that applying faeces will help in several respects, both in terms of adding other macronutrients and with adding organic matter to the soil. But even here the overall amounts of NPK may still not be what is needed by the crop and still may not be enough to replace all fertilisers - it entirely depends on the soil and the crop.

This whole subject is extremely complicated and site specific!

goeco wrote: Fact is that urine is not a balanced fertiliser. What I am trying to raise is that vermicomposting adds nutrients to the liquid effluent. By drying feces, UDDT systems make "active" biomass (a good carbon and nutrient source once decomposed), plus urine. There is a disconnect because urine is not a balanced fertiliser. In contrast, vermicomposting digesters should produce a NPK-balanced nutrient-rich effluent. The issue I have is that this has apparently not yet been quantified by published research.

What I am trying to explain is that a vermicomposting digester produces "stabilised" humus (a good soil amendment rich in carbon) that apparently has low levels of pathogens (again not quantified) and the bulk of fecal material is reduced to liquid which combines with urine to be a nutrient-balanced liquid fertiliser (with variable pathogen levels depending on what happens next). There are two options for the liquid, secondary treatment and surface drippers, or simply discharging directly to underground soakage trenches that feed suitable food crops like bananas that respond to water + balanced nutrients.

Mmm. This relates to another term we should be using when discussing amending things to soils - the idea of "nutrient availability". It is complicated chemistry, but basically it means that there are different forms of NPK, some of which can be taken up by the plants and some of which cannot. Part of the problem with urine is that urea is immediately available, so if the crop is not actually needing the nitrogen right now, it can easily be lost altogether from the soil. So composting (and also processes like vermicomposting) help by changing the availability of the nutrients. It sounds counter-intuitive, but these actually sometimes make the nutrients less available, so more of them are stored in the soil rather than being lost as I described above. So a farmer might find that the compost does not have a rapid effect on this season's crop as you might see with a bag of fertiliser, but there is a long term improvement in the fertility of the soil so in the long term the crop growth is improved.

So this is the difference between a mix of fresh urine and faeces and a compost (or vermicompost) - the material has been "stabilised". The organisms have also changed the physical structure of the material to make it more suitable for use in the soil.

Even if the balance of NPK in the urine is exactly what is needed by the crop, a lot of the nitrogen will be lost during storage and application, and if it isn't applied at exactly the right moment may have little effect on the crop growth. Of course this depends again on exactly what the situation is.

In contrast the nutrients in the compost have been stabilised, so there are fewer losses during application and the timing is less critical because of the long-term release of the nutrients.

By recycling balanced nutrients to crops, the risk of growth-limiting factors (especially lack of P) is reduced. One thing that needs to be clear is that by increasing productivity of land using liquid only ('booster'), organic matter (biomass or 'soil amender') levels are increased and so improve soil quality by being returned to the soil. Production of biomass is mostly limited by two factors, availability of water, and nutrient shortage. Abundance of some nutrients and shortage of others is no better than shortage of all nutrients.

cheers
Dean

That's correct, although we should be careful in suggesting that compost will solve all nutrient deficiencies in crops and the soil. Again, without knowing what those deficiencies are, we'd be operating in the dark. That said, because the nutrient availability in the stabilised compost/vermicompost has been changed, there is likely to be less of a problem with excess nutrients in the soil from compost than you'd get with an oversupply of urine or a commercial fertiliser. It's very difficult to add too much compost!

On the pathogen point, the best research I've seen suggests that worms alone not able to reduce pathogens to safe levels, in contrast to composting where the high temperatures kill them off.