I have my doubts as to whether immature compost would affect plant growth. Most published work on the agricultural benefits of using human faeces have been on (dewatered) sewage sludge and I have not heard of negative impacts related to the maturity of the material. My personal experience is that urine does not slow composting, although may lead to large amounts of ammonia release. I postulate that this is related to the size of the windrow, as the heat produced from big windrows/heaps is so big as to rapidly remove much of any moisture that is added.

Compost maturity is related to sanitation, stability and handling, I doubt it has anything to do with negative effects on crop growth. In some ways, immature compost may actually have more immediately available nutrients than mature compost, so one might expect better crop growth from fresh faeces than faecal compost (if one spread it at the right moment when the crops needed the nutrients). In a compost, the majority of the nutrients are going to be less available and slowly releasing to become available to the crop.

I think the conductivity and salinity is much more likely to be an issue. I had a look at the literature:

Karak give several precautions for using human urine including

higher application rates of human urine could increase the salinity and high electrical conductivity of the treated soils

from here: www.researchgate.net/profile/Tanmoy_Kara...9d113c2b59000000.pdf

This presentation from South Africa says that conductivity (salinity) is an issue at high application rates of human urine www.researchgate.net/profile/Funso_Kutu/...04cd0a6e26000000.pdf

So I think these suggest that the salinity of urine is a known issue. I wonder why some sources of urine are particularly salty.

I also wonder whether there would be a dilution (or other chemical) effect which would reduce or change the salinity of a mix of faeces and urine.

Thanks Elisabeth and Jörgen for bringing up that paper and the question of quantifying disease rates among UDDT users and impact on school children. Very interesting, and yes, more information is needed!

I just wanted to add in a note that at SOIL we thought that the plant stunting observed was due to the high salt content and not incomplete decomposition. The C:N ratio was around 10, indicating that it was fully decomposed but the conductivity was very high. Some of the SOIL folks would be curious to know specifically about how using urine as a means of pathogen treatment affects conductivity.

Thanks so much,
Monika

Thanks for the information, Elisabeth! I could also just clarify that I don't think UDDT toilets generally increase the risk of infection with parasites. I just wanted to illustrate that composting in general, and also composting toilet, does not automatically assure that the finished compost is pathogen free. The pathogen inactivation is depending on the temperature/moisture level of the compost.

Dear Jörgen,

Interesting discussion between you and Monika, thanks a lot.

The paper that you linked to caught my attention, but then I realised it is "only" that "famous" El Salvadore paper from 2006 (which we had discussed in some length back on the old EcosanRes Discussion Forum; I just checked the Yahoo group archive for it; for example this message from Hakan Jönsson in 2006: groups.yahoo.com/neo/groups/ecosanres/co...ations/messages/1141 )
(unfortunately, the archive is not openly accessible, only to those 800 people who were members at the time; that's one of the reasons why we moved to this forum in 2011)
Mind you, I had a look if anything needs to be copied across but the discussion was mainly just around how to improve pathogen kill in UDDTs. Hakan pointed out this:

+++

Dear Shirish,
As the team of Christine Moe has shown the pathogen reduction in solar toilets is good!
Ref: Longitudinal study of double vault urine diverting toilets and solar toilets in El Salvador*
Christine L. Moe, Ricardo Izurieta (Rollins School of Public Health of Emory University, USA)
www2.gtz.de/dokumente/bib/04-5004b.pdf
Ecosan regards,
Håkan

++++

Arno told me this:

As I recall this was a very mismanaged project and the toilets were not at all dry plus poorly maintained. I recall having met these authors and discussing this.

It's interesting because I had made a forum post earlier this year where I had asked:

Are there any studies that have shown more disease in UDDT users than in VIP users or even open defecators? This is something that I would find interesting, and alarming, but I don't think such research exists.

That post of mine is here:
forum.susana.org/forum/categories/34-uri...n-south-africa#12757

So thank you for bringing that El Salvadore study back to my attention. However, I don't think it is representative for UDDTs in general, but only for that particular case of poorly managed UDDTs in that particular project in El Salvadore.

What we'd really need is a survey of people's worm burden in several regions where UDDTs are used by many people. My hypothesis is that such a survey would show no higher rates of worm infections. But I guess we have too little research on helminth infections anyhow. We don't even yet have a clear picture on whether deworming has much of an impact on school children (something which I posted about here: forum.susana.org/forum/categories/159-in...as-much-of-an-impact)

Regards,
Elisabeth

There are normally very low concentration of pathogens in urine, unless there is some problems with the use of urine-diverting toilets and high crosscontamination of faeces. The purpose of mixing urine and compost would therefore be to ensure die-off of pathogens left in the compost. In case the temperature during composting has been low, the compost may contain high concentration of pathogens even though it is mature and look like soil. If the compost temperature has been high in all of the material, i.e. above 50 °C for 2 days between mixing, and mixed 5 times, there is no need for this type of post-treatment. If tomatoseeds start to grow in the composted material, this is an indication that also ascaris eggs have survived and that additional post-treatment is required.

Here is a link to a paper showing that prevalence of intestinal parasites was higher for UDDT users compared with non-UDDT users, due to handling and use of compost which has not reached high temperature and/or low enough moisture for ascaris inactivation.
www.ncbi.nlm.nih.gov/pubmed/17176347

+++++
Note by moderator: Details of the mentioned paper from 2006 are:

Association between intestinal parasitic infections and type of sanitation system in rural El Salvador.
Corrales LF1, Izurieta R, Moe CL.

Trop Med Int Health. 2006 Dec;11(12):1821-31.

Thanks Jörgen for your insight! I will pass on this info, and think it will spark some discussions as to if/how/when to add urine to the compost.

One question - in your 2nd paragraph when you talk about mixing the urine with mature compost in closed containers to avoid ammonia losses and ensure pathogen die-off - is this assuming that there are still pathogens left from the composting process, or that there are pathogens in the urine?

Thanks so much,
Monika

Hi Monika! Generally I would not recommend to combine addition of urine with composting at the same time. Two reasons for this: 1) The ammonia from urine does not only inactivate pathogens, but also the microorganisms responsible for composting. 2) The ammonia in urine is mainly lost to the air during composting, as composting requires air. Ammonia treatment for pathogen inactivation requires a closed container, which is not compatible with composting.

One option is to first compost the material, and then mix it with urine when it the compost is mature. After mixing urine and compost, it should be stored in a closed storage with minimal air exchange to avoid ammonia losses. This will ensure pathogen die-off, but the storage/treatment time required depend on ammonia concentration and temperature.

I guess that the urine has slowed down the compost process in your case. When this compost was used as soil improvement it showed stunded growth, probably because the degradation/composting continued during plant growht and this requires some nitrogen, so less nitrogen was available for plant growth. I'm not an expert on these things, but this would be my guess. In a normal case, this should not be a problem when sanitizing with ammonia/urine, as the closed storage ensures a high nitrogen concentration in the final product. However, while compost can be used as soil alone more or less, ammonia sanitized material need to be mixed with soil in order to dilute it.

Note by moderator:
This post was originally in this thread about the PhD defence of Jörgen:
forum.susana.org/forum/categories/53-fae...ture-q-at-slu-sweden
+++++++++

Thanks Jörgen for posting your defense slides - I'm sorry I missed your presentation.

This is very interesting work on the potential to sanitize sludge with urine. At the SOIL operations in Haiti we had tested 2 different batches of compost produced. Urine was added to one pile located in a structure with a roof. The leachate was collected and continuously re-added to this pile. The other pile had no adding of leachate or urine, and did not have a roof over it, thus receiving rain. The compost results showed high conductivity and stunted growth in a cucumber bioassay in the pile with the re-addition of leachate and urine, versus normal conductivity and cucumber growth in the control.

It seems that as you explore this topic, the quality of reused biosolids regarding the effects of urine addition could be a concern to address in the future. I (and the SOIL team) would definitely be curious to see more research on this! Thanks.