In terms of composting, I think meso-scale (1000 to 10,000 households) monitored sites can produce consistently safe compost, and the available evidence suggests that these are much safer than any dispersed and unmonitored system. I do not believe that the only safe forms of faecal treatment are massive centralised treatment sites.

On your other point, I believe in the need for minimum sanitary standards and that systems which do not meet the standards should not be installed. Basic composting toilets are technology that goes back at least 100 years and have been shown to fail over and over again, and yet are still being installed and used. Sanitation seems to me to be one of very few areas in development where solutions are supplied on the basis that they are better-than-nothing rather than that they meet minimum standards.

In any really bad situation almost any solution, however objectively bad, is better. But surely we want good solutions not just any old solution?


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Note by moderator: the conversation then moved towards UDDTs and health risks and has been moved to here:
forum.susana.org/forum/categories/34-uri...wini-in-south-africa

Hi Joe,
I agree with you on the BEST solution.

Large industrial composting fecal sludge composting are the best information we have for the best possible situation for composting of feces, often with forced aeration and frequent batch testing.

BUT .. and this but I would like to make bigger than it is possible here.

Is it your opinion that this is the only solution which is acceptable for non sewered poor areas? Thinking further - would you say it is better to serve 10.000 with a perfect solution or 100.000 with a very safe, but not totally safe solution? Is the effect you can have with a second best solution (may be only for a couple of years) but coming to many people not better than a perfect solution for some and no solution for the others? I am convinced of the first you seem to be more fond of the second.

Just thinking
Christoph

christoph wrote: When wastewater sludge is not “sterilized” why should we do that with composting toilets (to come back to this thread)?-

Large industrial composting faecal sludge composting are the best information we have for the best possible situation for composting of faeces, often with forced aeration and frequent batch testing.

In constrast there are very few studies of small composting and composting toilet systems, and those that exist are not encouraging on pathogen kill.

If large monitored, batch tested composting cannot guarantee that pathogen regrowth will not happen in stored material, then the sub-optimal conditions found inside a composting toilet system (limited oxygen, no monitoring etc) will have even more risk of regrowth. Any unmonitored system is going to be worse than a monitored, batch tested system - so if there is a problem identified on the large scale, it is going to be worse on a suboptimal system.


There is no good evidence that prolonged storage produces safe faeces. There is little good evidence that composting toilets produce safe faeces. It is about risk, and as shown by the Stenström risk assessment document I mentioned above, the use of composting toilets produce material that is high risk to handle and high risk to reuse.

Hajo,

thanks for pointing out that my comment was misleading. I intended to say – I like better the UDDT (technology) than the composting (technology) as you need smaller recipients to get good results. It has to be made very clear that UDDT and Composting Toilets are two different (somehow similar) technologies with different final results, aims and needs.
Chris is talking now about “his” sacks – (not composting), Joe is rambling (as always) about sterile end products (although I am with him about pointing out to be aware of the danger of helminth eggs in general in fecal biosolids) bringing in examples from wastewater sludge.

For someone who is not following these discussions it must be confusing. So for those:

UDDT and Composting toilets are two different things – often in common language mixed up. Both offer a product which seems visually (not looking in detail) the same, but they are completely different. Arno pointed out the need of composting toilets for structure material – no need in UDDT. UDDT need the separation of urine and feces composting toilets do have that sometimes, sometimes not. But have a look at Wikipedia if you are confused.

Back to “us”…. Joe - Maybe in another thread I would like to get to know your preferred vision for household orientated non sewer sanitation solution and especially how feces final destination should be done (in poor settlement areas). It is easy to say “not perfect”, but what is good enough? I think we have to be realistic. When wastewater sludge is not “sterilized” why should we do that with composting toilets (to come back to this thread)?-

Regards
Christoph

P.S. 30 mi later .... only now I saw that Joe already cleared the missunderstanding - Hajo no worries - if you think something is wrong point it out I think we HAVE to do that.

Composting is commonly used as an effective means of stabilizing wastewater biosolids and reducing pathogens to very low concentrations. However, it has been shown that under certain conditions Salmonella can regrow in previously composted biosolids. Growth of seeded Salmonella typhimurium in composted biosolids ranging from two weeks to two years maturity was monitored. Results from sterile and non-sterile composted biosolids were compared. Seeded S. typhimurium colonized rapidly in sterilized biosolids reaching a maximum population density of more than 10( 8 ) g(-1). Growth of seeded S. typhimurium was suppressed in non-sterilized compost with a maximum population density of less than 10 ( 3) g(-1). There was a significant decline in the growth rate of seeded Salmonella in sterilized compost when the compost was stored, suggesting that bio-available nutrients declined with storage. However, in non-sterilized compost this was not the case. This suggests that the indigenous microflora play a significant role in suppression of Salmonella regrowth in composted biosolids. There was a strong negative correlation (-0.85) between the Salmonella inactivation rate and the maturity of compost in non-sterilized compost. The Salmonella inactivation rate was seven times higher in biosolids composting for two weeks as compared to compost stored for two years. This suggests that the antagonistic effect of indigenous microorganisms towards Salmonella declined with compost storage. It was concluded that all composted biosolids had a Salmonella regrowth potential. However, the indigenous microflora significantly reduced this regrowth potential. Long-term storage of compost is not recommended as this may increase the pathogen regrowth potential.

abstract here: www.ncbi.nlm.nih.gov/pubmed/11235886

Regrowth of Salmonella occurs under certain conditions in stored biosolids (Hussong et al., 1985; Gibbs et al., 1997), bagged biosolids based products (Skanavis and Yanko,1994), composted biosolids (Sidhu et al., 2001) and soils treated with biosolids (Zaleski et al., 2005), which adds to its unpredictable behavior in biosolids.

Sahlstrom et al. (2004) carried out a year long survey of 8 wastewater treatment plants in Sweden for the presence of E. coli O157:H7 in sewage sludges. They reported it to be present in 2% of raw sludges but not in anaerobically digested and composted biosolids. It
appears that E. coli O157:H7 numbers in biosolids are not expected to be high. However, they are known to survive on pasture and in stored animal manure for more than 11 weeks (Ogden et al., 2002; Kudva et al., 1998). Prolonged survival for more than 6 months can be expected in winter (Avery et al., 2004). Regrowth of E. coli O157:H7, like other enteric bacteria in biosolids or sludge applied to the land, is also possible under certain conditions.

Campylobacter are also reported to enter a viable but non-culturable (VBNC) form under conditions of environmental stress (Medema et al., 1992)

Abstract here: www.sciencedirect.com/science/article/pii/S0160412008001244

Stabilised wastewaser sludge (biosolids) has beneficial re-use properties but these are limited by the presence of human pathogens. In this study soil amendment with biosolids and storage of biosolids prior to re-use were examined as disposal and treatment options. In a soil amendment trial biosolids were mixed with sandy soil and monitored for 37 weeks. In two storage trials biosolids were stored in piles 1m high and monitored for <60 weeks. Included in the monitoring programme were tests to determine the concentrations of faecal coliforms, faecal streptococci and salmonellae. In both the soil amendment trials and biosolids storage trials, concentrations of indicator organisms and salmonellae decreased through an extended hot, dry summer period. Although these organisms were not detected in the majority of samples taken during the summer, repopulation of faecal coliforms and salmonellae occurred in the trials following rainfall at the beginning of the winter. In the case of one of the storage trials repopulation occurred following a period of 50 weeks when salmonellae and faecal coliforms were not detected. When repopulation occurred, faecal coliform concentrations increased to higher than those at the beginning of the trials. These results suggest that faecal coliforms and salmonellae were at undetectable concentrations through the summer period but were able to grow when provided with favourable conditions. From this limited trial it was concluded that soil amended with biosolids could not be considered free from pathogens for at least one year following amendment.

Abstract here: www.sciencedirect.com/science/article/pii/S0273122397002710

Hi Joe,

What studies did you read?
Why would anyone expect the finished ''biosolids'' (which are almost indistinguishable from soil) to become sterile?
What would pathogenic microbes adapted to living in water without oxygen in our guts have to do in a pile of dry soil? Plus it is obvious that if there is new fecal contamination, the previous material is no longer safe.
In all such studies, we should keep track of what climate they are carried out in and what sort of microorganisms are added with the cover material (or if natural beneficial decomposer microbes are expected to come out of nowhere).

Edit: We have done microscopic studies of our finished ''biosolids'', after having used this same ''soil'' as cover material (with diverse soil microbes), in a warm, moist, tropical environment, and we have never found Ascaris eggs beyond 4 months of storage in woven, polypropylene sacks, despite Ascaris being abundant at the start. Researchers who would like to study our system here in Amazonian Ecuador are very welcome, especially those who do metagenomics.

Best wishes,
Chris Canaday

Hajo, I generally agree.

I was even reading studies yesterday which suggest that faeces left in storage for more than 2 years may well have measured pathogens below "safe" levels, but that they have found to be rapidly reinocculated with the pathogens again - perhaps from additional human faeces, animals, leachates etc. The theory is that old faeces may have become almost microbially sterile, so that there is nothing to compete with the pathogen microbes if they reinoculate.

Given that viable helminth survive for many years in appropriate media, I think the idea that storage is a safe way to sanitise human faeces is basically disproven. If projects are not directly monitoring the pathogens, it seems to me that these systems may well not be robust enough to completely reduce all pathogens to safe levels.

Volume reduction is a factor, but I'd probably agree that dehydration is a more efficient way to do this in terms of space required. But to me, the benefits of volume reduction are far lower than the possible risks of pathogen transfer by the reuse of poorly sanitised faeces.

joeturner wrote: hajo, I think you might be misunderstanding christoph -

I think he (christoph) was saying he prefers the UDDT to the Clivus Multrum composting toilet system because it (the Clivus Multrum) needs a large composting compartment.

joe, I think you are most likely right..

I was even wondering how Christoph could mistake a UDDT for a composting toilet... Sorry, Christoph!

.. where I think even the Clivus Multrum is not a composting toilet in the sense of producing valuable compost for re-use: neither moisture, nor temperature, nor N:C composition, nor aeration are controlled to the extend to ensure a composting process. For me it is a degredation process with the aim to reduce volumes considerably (and successfully) as the website states.

ciao, Hajo

hajo, I think you might be misunderstanding christoph -

I think he (christoph) was saying he prefers the UDDT to the Clivus Multrum composting toilet system because it (the Clivus Multrum) needs a large composting compartment.

OK, if material is stored for decades, that might be a different thing - but how many ecosan and composting toilet programmes plan for storage for that length of time?

It is true that soil application acts as another barrier, but the risk assessments (which I agree are inadequate) that we have suggest that it is the emptying and handling of potentially imperfectly composted faeces that may be high risk.

Microbial Exposure and Health Assessments in Sanitation Technologies and Systems. 2011 Stenström et al fig 8 page 51

I also think that the issues are different in North America, Europe etc than applications elsewhere for important reasons: the low level of endemic faecal pathogens in the population, the widespread availablility of healthcare, better overall hygiene awareness etc.

Hence I can accept that composting toilets in Elisabeth's garden, or those advocate by Kai in the USA etc are unlikely to be a major health hazard - whilst at the same time believing that it is an inappropriate technology in many other situations.

Hi Joe
You may be right. I think this is the case for most short-term batch type composts where turning is not normally carried out. There will never be 100% die off of pathogens. A secondary step such as further drying and storage or even further composting or heat treatment should be carried for public toilets for these rapid conmposters.

For household-based systems where the compost remains in the household garden, the risk of disease from reuse is very low. And don't forget the aspect of how compost is to be used in gardens. It is the soil that is receiving the compost and that functions as an additional treatment. So sensible risk assessment is necessary, unfortunately little work has been done on this.

But the Clivus is different from anything else. It stores material for years prior to reuse. The original models went for decades prior to emptying.

The Fossa alterna produces sweet smelling soil and has similar levels of organics that the Clivus has.

christoph wrote: So I can see that it might be worthwhile to define better what exactly is a composting toilet. I referred my comments to the "Clivus Multrum Type" composting toilet which are the only ones I really know. Due to their large composting compartments I do prefer UDDT, but that is another story.

CP

Sorry, Christoph, for 'Nit Picking' but UDDTs (under their current designs and operations) are NOT composting toilets therefore you should not prefer UDDT due to their 'large composting compartment'. They are de-hydrating toilets as the name says which in itself is opposite to composting (which requires a specific moisture content).

Whenever people call UDDTs 'composting toilets' we have to object!

ciao, Hajo