Multiple barrier concept, QMRA (Quantitative Microbial Risk Assessment), acceptable risk for safe reuse

  • Florian
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

Good you join the discussion!

joeturner wrote: Advocates of 'humanure' insist that composting toilets kill pathogens when they cannot possibly do so.


You're right that most on-site sanitation technologies do not reduce pathogens to 0. But you are fighting windmills in insisting that everybody here thinks othererwise.

I think "advocates of 'humanure'" usually rather say that different on-site technologies reduce pathogens to very low levels, so that with some additional measures (multi-barrier concept!) the materiales can be safely reused (or disposed off safely).

Let me give you another example: I assume you live in Europe. So you are useing a sanitation system, whose treatment in most cases does not bring down pathogen levels to 0. Most modern wastewater treatment plants in Europe have no disinfection and thus a much lower pathogen removel rate as, for instance, a good UDDT toilet. But that's not a problem at all, as there are good other saftey measures in place.

I think the important part is that ecosan implies dispersed systems without any form of testing


Properly controling individual sanitation systems is indeed a challenge. But again, in Europe or the US, there are very good systems in place to manage dispersed individual sanitation systems. So it is possible to do this safely.

On the other hand, in many countries where monitoring and management of dispersed system is bad, because of weak capacities of administrations there, the very same happens also with centralised sanitation systems.

So if sanitation systems are safe or not, is not a questions of centralised vs dispersed, or ecosan vs. something else. The question is how to make things work.


The following user(s) like this post: muench, canaday, christoph
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  • joeturner
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

I am not suggesting that the risk should be 0 and the studies I have pointed out do not work on that basis. In fact the way to assess systems microbiologically is using Quantative Microbiological Risk Assessment (QMRA) which is based on acceptable dose rates, which is calculated by the socially acceptable number of infections in a community.

Therefore talking about a risk of zero is not only impossible but not the point I am making - which is that the sector needs acceptable standards so that it is possible to tell when faeces is treated and when it is not and when the risks of handling and spreading are acceptable. Again, studies which use the best information and are based on QMRA suggest that UDDT and composting toilets do not reliably kill pathogens to safe levels.

In Europe the calculation is totally different due to the standards of healthcare available and the lack of endemic faecal diseases.
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  • joeturner
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Re: Multiple barrier concept, QMRA (Quantitative Microbial Risk Assessment), acceptable risk for safe reuse

I would also say that the multiple barrier system is a good one, but what barriers exist in most ecosan systems?
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  • christoph
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

Joe I´m with you on many aspects of not beeing safe for reuse but as Florian pointed out ...for many here that is not the main focus .....and for me the ECOSAN = UDDT discussion is of the past decade.

in most ecosan systems

But you always want us to be precise and now you begin with a sentence like the above.
Could you define ecosan systems better? I have the impression you mean UDDT.

If you ask for the multiple barriers of UDDT, my view is as followes:
  • the feces fall into a separated chamber (barrier one)
  • they stay there until dried out to a good level which makes handling easy (second barrier)
  • the cleaning out should be done with mask and gloves (third barrier)
  • and burying with a cover of 30 cm should be done (fourth barrier)
Is this less save than a treatment lagoon which delivers without disinfection (most do not comply with fecal coliforms criteria - but yes normally for helminth eggs)

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Christoph
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  • joeturner
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

Christoph, I am talking about any system of dispersed sanitation whereby users collect, treat and handle their own faeces. In my view that includes UDDTs, composting toilets - but not systems such as meso scale [monitored] co-composting sites. Most ecosan systems would fit within that, would you not agree?

In terms of the barriers, your first two points are not additional barriers because that is the normal operation of the UDDT. Research from South Africa suggests that normally operated UDDTs do not reduce pathogens to safe levels. In my view this is because it is impossible to tell if stored faeces in a UDDT has been consistently subject to the drying effect and therefore pathogens persist.

The use of safety equipment is a barrier to at-risk workers emptying the UDDTs however they are not always available or foolproof. Also this is not a barrier to other at-risk groups. But yes, risk is reduced if safety equipment is used.

Again placement of the treated faeces can be a barrier, but this depends on consistent practice and knowledge of risky behaviours.

I think these are pretty poor barriers to infection risk from faeces where it is unknown how well pathogens have been destroyed and depend on correct use and behaviour by everyone all of the time.

I do not know about other systems, I assume the problem with a lack of safety standards is the same.

That said it seems to me that it is much more likely that processes can be developed in meso scale composting, vermiculture and other systems with some monitoring to reduce risk to acceptable levels than small dispersed unmonitored systems.
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  • christoph
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

Sorry Joe, but you are (uncommonly) dribbling with words!
a)

I am talking about any system of dispersed sanitation

You consider any dispersed sanitation system = Ecosan? I am sure you know the difference.
b)
As for the barriers. This depends on the point of view. The first two are for me the most important barriers in terms of sanitation, as they bring the fecal matter to a level where it is MUCH less dangerous as for instance fecal sludge. Than you come to the emptying. I hope you agree that cleaning out a UDDT (with gloves and mouth protection) is WAY more secure than pumping out a fecal sludge tank with handpumps or manual cleaning of pits (even with protection). Therefore the second barrier had large influence.
And for the final destination....I am totally with you (and I think that is the point where we really have the same view) that a centralized collection system would be the best way to go.

c)
There you write about vermicomposting - from my knowledge (i guess we already discussed that somewhere) vermicomposting does not have any influence on the pathogen aspect.

So please indicate better what is the point which makes you so upset.
Is it the lack of centralized systems for ANY sanitation ...most of us feel with you although this for me has nothing to do with Ecosan or sustainable sanitation. You can do a centralized system wasting a lot of energy and other resources and therefore not complying with criteria of sustainability nor ecological aspects but having a safe sanitation system.

I like this discussion as it points to some basic conflicts which still exist (although I did not expect them from your side)

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Christoph
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  • joeturner
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

I apologise for dribbling. Are all dispersed systems ecosan? No. Are all ecosan systems dispersed? Yes - because I do not consider meso-scale composting to be ecosan. I think the problem is that they are dispersed and unmonitored.
I have seen a study looking at the risks to sanitation workers from emptying UDDTs, I will try to find it again tomorrow - the point is not whether gloves reduce the risks but whether the risks are reduced to acceptable levels.

Unless there are agreed standards of risk, I cannot really see how anything can be said other than that relative risks are reduced to one set of at-risk groups.

I think meso/medium/community/village scale sanitation is possible but that small unmonitored dispersed systems are not killing pathogens to safe levels. Small/household scale systems which claim to be treating faeces are not.

I would also point out that I was responding to the blog from the Gates Foundation (see sanitation.joetnr.net/sanitation-good-in-parts/ and forum.susana.org/forum/categories/80-glo...anitation-indicators ) which pointed to the importance of treated faeces. At present we have a division between Open Defecation, Unimproved Sanitation and Improved Sanitation. It is possible to have toilets and even improved sanitation but without standards to determine when faeces is treated, it is impossible to say whether any system is really safe.
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  • arno
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

UDDTs are designed primarily to do three things when it comes to faeces: to contain the faeces, to dry them and with the addition of woodash (high pH KOH) following each defecation, reduce flies, odor and pathogens. Once one of the 2 vaults is full it is topped up with woodash and left for 6 months. The risks in emptying such a toilet (each vault is emptied once every 12 months) are much lower than emptying pit latrines and septic tanks that preserve pathogens in the cool moist/wet environment. Once emptied the dried mass from a UDDT is then taken to a green compost to undergo thermal treatment up over 50-60 degrees celsius. The UDDTs in the Sahel countries and other dry and hot climates are even greater successes since they become almost pathogen-free within just a few months under the furnace-like dry conditions within the raised above-ground vault. Fossa alternas and Arbor loos are soil-composting ecosan toilets and also are given long cycles (one year and upwards) to reduce pathogens. The intestinal bacteria are no competition to the adapted and aggressive soil bacteria plus all the other organisms in soil. The eggs of helminth worms can theoretically persist in most environments but will die off at temperatures above 60 degrees celsius. But with high pH (from woodash), dryness and temperature ca 45 degrees, they can be killed off. www.sciencedirect.com/science/article/pii/S0043135412004101 . No other sanitation system comes close to UDDTs in the fight against Helminth parasites. That we have upwards of 2 billion humans that live with round worms is living proof that our hygienic practices in high exposure areas require much improvement.

In cases of patients with dangerous viruses like Ebola, Coronaviruses (SARS), Polio, etc. toilets with containment and heat are necessary (eg dry incinerator toilets www.siriuseco.no/en-us/frontpage.aspx ) in order to provide 100% safety from faecal transmission. But these are not available or affordable in most parts of the world. So to provide both safe containment and treatment, the brick vault UDDT toilet combined with heat treatment using hot coals to reach temperatures of over 60 celsius in the vault would be an appropriate methodology to eliminate transmission via faeces. This to my knowledge has not yet been tried at scale. Along with sterilized surfaces and hand-washing transmission would be further reduced.

Arno Rosemarin PhD
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  • Florian
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

muench wrote: Oh and I still disagree with Florian's "laissez-faire" approach when it comes to definitions of terms.


Well, this discussion illulstrates your point well, Elisabeth, so I guess you're right. Indiscrimate use of terms results in a lot of confusion. But then, Joe could really have made clear by now what exactly he means when talking about ecosan.

A few more reactions to Joe's comments here.

joeturner wrote: I am not suggesting that the risk should be 0 and the studies I have pointed out do not work on that basis. In fact the way to assess systems microbiologically is using Quantative Microbiological Risk Assessment which is based on acceptable dose rates, which is calculated by the socially acceptable number of infections in a community.

We have a quite detailed WHO guideline, which precicely uses these concepts to define health based targes and deduces standards and guidance on reuse of excreta. All the talk about multi-barrier systems is based on these guidelines.

joeturner wrote: It is possible to have toilets and even improved sanitation but without standards to determine when faeces is treated, it is impossible to say whether any system is really safe.

Again here is your exclusive focus on treatment (in toilets). UDDT toilets (asuming we still talk about this) are just part of a system. The complete system involves other treatment steps (like your prefered "meso-scale composting") or other protection measures (e.g. the ones listed by Christoph). You have to look at the whole system to determine if it's safe or not. Only looking at one component of the system, the toilet, is nonsense.

To come back to the example of Europe. As I said, the treatment is not safe at all and wastewater treatment plants discharge quite a lot of pathogens to the surface waters, but still the whole system certainly is quite safe. Why? Not because we have no pathogens in wastewater, as you assumed (we do!), but because plenty of other barriers are in place. The most important barrier is that nobody drinks directly from rivers, but that all drinking water is disinfected. Another safty measure is that bathing waters are monitored and flagged red when risks are present. And in some situations when it is really needed for safety, wastewater is indeed disinfected (e.g. when the discharge point is just upstream of a popular bathing spot).

So, treatment is just one safety measure in a system of multiple barriers. The decision on the treatment performance (pathogen removal rate) needed depends on the other components of the system and on economic and social considerations. Sometimes this may be 100 % pathogen removel, sometimes not.

Christoph, I am talking about any system of dispersed sanitation whereby users collect, treat and handle their own faeces.

Of course ecosan systems are not limited to such systems, as other have pointed out, but even such systems can be perfectly safe. E.g. a familiy owned UDDT toilet, where users store feces removed from chambers for addtional time before reusing it, or reuse it directly in the way Christoph described it, or just bury it somehwere in the garden.

Why this can't be a safe system? The critical part is that people have to handle fecal material which may still contain some pathogens, agreed. But handling dried fecal material, that has been in a chamber for half a year without addition of fresh feaces, is much less dangerous than cleaning a toilet when a family member has diarhoea, or changing diapers of your sick child. So why should we trust in people being able to wash their hands after cleaning their toilet, but not after removing dried feces from a vault?

Btw, same is true for reuse practice. People handle all sorts of very dangerous stuff (pesticides, fertilizers) when growing crops. It's commonly accepted that the risk can be reduced to acceptable levels by appropriate protection measures. Why should this be different for fertiser containing some residual pathogens?


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  • JKMakowka
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

joeturner wrote: Therefore talking about a risk of zero is not only impossible but not the point I am making - which is that the sector needs acceptable standards so that it is possible to tell when faeces is treated and when it is not and when the risks of handling and spreading are acceptable.


Maybe a side-point, but agreeing on these standards would be next to impossible as "acceptable risk" is very relative to the overall conditions and alternatives.

In the water supply sector, there is such a standard, i.e. the WHO guidelines and it is leading to nothing but headaches in developing countries. Quite often people even choose consciously not to test at all, as attaining the standards would be impossible given the resource constraints, and the attained quality is obviously better than what people used before.

Similar issues I see with waste-water treatment plant effluents, where national standards that are usually derived from some global "best practise" guidelines, and are only smiled at by most working on waste water treatment in these countries (except for large donor funded projects that do use international standards, but they are rarely maintained a few years down the road).

As others have argued: everyone seeks to minimize the risks, but all is relative to the conditions and other benefits derived. Given the huge lack of sanitation we can also not afford the luxuries of too strict standards based on theoretical concepts of totally safe treatment or reuse.

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  • joeturner
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

Florian wrote: Again here is your exclusive focus on treatment (in toilets). UDDT toilets (asuming we still talk about this) are just part of a system. The complete system involves other treatment steps (like your prefered "meso-scale composting") or other protection measures (e.g. the ones listed by Christoph). You have to look at the whole system to determine if it's safe or not. Only looking at one component of the system, the toilet, is nonsense.


I agree with this. So, clearly, systems should not exist where composting toilets and/or UDDTs are considered sufficient treatment for faecal wastes to be reused in agriculture. I accept that they can be part of a 'whole system', but how often does that actually happen?

To come back to the example of Europe. As I said, the treatment is not safe at all and wastewater treatment plants discharge quite a lot of pathogens to the surface waters, but still the whole system certainly is quite safe. Why? Not because we have no pathogens in wastewater, as you assumed (we do!), but because plenty of other barriers are in place. The most important barrier is that nobody drinks directly from rivers, but that all drinking water is disinfected. Another safty measure is that bathing waters are monitored and flagged red when risks are present. And in some situations when it is really needed for safety, wastewater is indeed disinfected (e.g. when the discharge point is just upstream of a popular bathing spot).


Excuse me, I have not assumed that there are no pathogens in wastewater. In sewage treatment works in the UK, where I have worked studying the composting of faeces with extensive suites of microbiological tests, there certainly are faecal pathogens. But they are at much lower levels than those found in developing countries and the worst pathogens are not endemic.

Hence it is possible to imperfectly reduce pathogen levels in a composting toilet in the UK, Sweden, Germany and elsewhere and - with other barriers in place - end up with a situation where there is a faecal waste that is not a high risk.

That says nothing about the effectiveness of a composting toilet as treatment in a situation where the pathogen loading is much higher, where pathogens are endemic, where there is little healthcare and where there are few other infection barriers in place.

So, treatment is just one safety measure in a system of multiple barriers. The decision on the treatment performance (pathogen removal rate) needed depends on the other components of the system and on economic and social considerations. Sometimes this may be 100 % pathogen removel, sometimes not.


I would say that treatment is overwhelmingly the best safety measure in a system of multiple barriers. It does not take very much for other barriers - such as gloves being used by sanitation workers - to fail.

Of course ecosan systems are not limited to such systems, as other have pointed out, but even such systems can be perfectly safe. E.g. a familiy owned UDDT toilet, where users store feces removed from chambers for addtional time before reusing it, or reuse it directly in the way Christoph described it, or just bury it somehwere in the garden.


On what basis are you saying that? How are you measuring what is 'perfectly safe'?

Why this can't be a safe system? The critical part is that people have to handle fecal material which may still contain some pathogens, agreed. But handling dried fecal material, that has been in a chamber for half a year without addition of fresh feaces, is much less dangerous than cleaning a toilet when a family member has diarhoea, or changing diapers of your sick child. So why should we trust in people being able to wash their hands after cleaning their toilet, but not after removing dried feces from a vault?


I don't see how relative risks with other risky behaviours is relevant.

Btw, same is true for reuse practice. People handle all sorts of very dangerous stuff (pesticides, fertilizers) when growing crops. It's commonly accepted that the risk can be reduced to acceptable levels by appropriate protection measures. Why should this be different for fertilier containing some residual pathogens?


Fertilizers are manufactured products produced under controlled conditions. Faecal wastes are not. You are comparing apples with eggs.
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  • Florian
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Re: Ecosan - what is it really? And what is the problem with ecosan? Is there a problem? Too much ecosan in SuSanA?

On what basis are you saying that? How are you measuring what is 'perfectly safe'?


As already said, on the basis of the multi-barrier concept as recommended by the WHO guideline.

I don't see how relative risks with other risky behaviours is relevant.

Fertilizers are manufactured products produced under controlled conditions. Faecal wastes are not. You are comparing apples with eggs.


I'm not comparing apples with eggs, I'm talking about the feasbility of protection measures. You seem to have the opinion that systems, where people need to handle partly treated feces themselves, are unsafe by principle. Yet we trust in people to do themselves much more risky things like cleaning their toilet or spraying pesticides on their tomatoes.

As for the ecosan defintion, no need to prove your point with the quotes. Yes, many people still use the more historic definition ecosan = UDDT. The understanding of the Susana comumnity of the term has evolved into a broader definition, as quoted above several times. You just just should make clear what exactly you are talking about when saying things like "ecosan is not safe", in particular as you also defined elsewhere "ecosan = shitting in a bucket".


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