Level of tolerable risk in a reuse context?

  • Florian
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

joeturner wrote: I'm really interested to know whether anyone thinks this is a success. On the one hand, the number of infections have reduced, but on the other, 0.7 infections per person per year seems to me to still be an unacceptable rate. And if that is true, what is an acceptable rate for these systems?


Hi Joe,
I think you are quoting results from different studies that are not directly related. Eg. the

89.5% of the urine diversion latrines contained microbial pathogens

were about parasites only, whereas the infection rates were about diarrhea cases.

I agree that 0.7 infections per person still sounds like too much. But if that result now points to a problem of the UDDTs or if the infections are caused somewhere else (water supply, personal hygiene, food hygiene etc.) can't be said from the quoted results alone.
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  • joeturner
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

Florian, that is fair comment, although the comparison is between communities that do not have any WASH interventions and those that have VIP plus other interventions.

For the sake of argument, if the only difference between the communities had been the presence of VIP latrines, would you say that was a success or failure?
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

joeturner wrote: For the sake of argument, if the only difference between the communities had been the presence of VIP latrines, would you say that was a success or failure?


Hi Joe, I rather tend towards considering the results as indicating success. After all the study proves a real impact of WASH interventions (reduction by half of diarrhoa incidence). If the result is ok in asolute terms, or if it rather indicates that there is still a lot to improve, I do not know.


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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

Florian, I suppose the question I'm asking with all these technologies is how you (or anyone else) is assessing whether the complexity is worth it for the results. How much better would TPS have to be than what you currently use to be worth developing systems to include lacto-fermentation and charcoal production?
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

I was imagining that storage was impractical - how much of the compost would remain after 10 years?

I think the material needs to be used on permanent non-food crops, ideally dug into the ground, and I think Ralf is saying that if you use the material on land (say forestry), you shouldn't then reuse it for food crops for 10 years.

Of course, the problem here is that to transport it and to dig it into the ground requires handling, which is a major hazard.

Unfortunately I think this means that our systems are broken. Either we need systems which are better at sterilising the feces properly, or we need to develop much more integrated sludge-agricultural systems whereby the feces can be safely disposed of.

Again, I think maybe we need to change the terms of the conversation. Urine is microbially much safer than feces and contains most of the useful plant nutrients. So we need to develop a model of reuse of urine and safe disposal of feces.
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

I agree, a system with 10 years storage time (or use restriction) would hardly be feasible in practice on a larger scale. Perhaps for wine or whiskey, but rather not for feaces, fertilzer and soil. If 10 years storage would really be necessary, then treatment or disposal would be more feasible ways. However, I understand that this 10 years time brought forward by Ralf is not something that all (or even many)experts agree on.


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  • joeturner
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

Florian wrote: I understand that this 10 years time brought forward by Ralf is not something that all (or even many)experts agree on.


I agree with this - although there is a very dramatic difference between the usual advice on reuse from many ecosan (and dry toilet) systems - which usually suggests (usually unspecified) reuse after storage for 3 months to 2 years - and Ralf's suggestion that the material should be treated as hazardous for much longer and that it may even have an effect on soil in which it is applied.

I think there is a lot of evidence to suggest that 2 year storage time is too little - and that secondary treatment is necessary. A properly monitored aerobic co-composted sludge is not so much of a hazard providing it is not directly consumed, in my opinion. However, I have my doubts how often co-composting systems are working correctly, hence I would guess that is makes sense to assume that they're often not properly sterlising the feces. If they're not being batch tested, I'm not sure how you ever could know how sterile the end product is.

I agree that is not the same as saying there should be a 10 year storage (or limit to land use), however I'm not sure that is bad advice to allow a margin for safety.
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

joeturner wrote: I think there is a lot of evidence to suggest that 2 year storage time is too little - and that secondary treatment is necessary.

Well, I think there is at least as much evidence supporting the currently used recommendations.

joeturner wrote: However, I have my doubts how often co-composting systems are working correctly, hence I would guess that is makes sense to assume that they're often not properly sterlising the feces. If they're not being batch tested, I'm not sure how you ever could know how sterile the end product is.

This is why storage is so popular as safety measure. Much more easy to control in practice.

joeturner wrote: I agree that is not the same as saying there should be a 10 year storage (or limit to land use), however I'm not sure that is bad advice to allow a margin for safety.

It's all about weighting relative risks and beneftis. Putting requirements too high will make reuse impossible. If you want reuse happen, then you need to put forward saftey measures that are approriate and feasible, but not extreme and prohibitive.

A good example are our favorite Ascaris eggs. Very hard to kill all of them, treatments that want to assure 100% of Ascaris elimination will always be complicated or expensive. On the other side, Ascaris infections are far from being deadly. They become problematic only if they are extreme and widespread.
So WHO thinks the benefit of reuse (e.g. of large scale wastewater irrigation) outweights the remaining small disease burden caused by 1 Ascaris egg per g soil or L water.

Now, if you would require 0 Ascaris eggs in water used for irrigation, treating wastewater to that level would not be possible at reasonable costs. Thus irrigation with wastewater would need to be prohibited. It may happen then that farmers continue to irrigate illegally with raw wastwater. The final health impact of extremely strict guidelines can therefore be worse than of more pragmatic ones.


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  • joeturner
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

Florian wrote: Well, I think there is at least as much evidence supporting the currently used recommendations.


I'd be interested to hear some. I don't think I've seen anything which suggests the storage recommendations are robust.

joeturner wrote: This is why storage is so popular as safety measure. Much more easy to control in practice.


Easier to control or easier to show you've done it? I think composting is far more robust than storage.

joeturner wrote: It's all about weighting relative risks and beneftis. Putting requirements too high will make reuse impossible. If you want reuse happen, then you need to put forward saftey measures that are approriate and feasible, but not extreme and prohibitive.


It depends what the focus should be. I've made it clear that I think the focus is wrong and that spreading untreated or part treated sludge is an infection risk. I don't think we can [simply] talk about risk when we're talking about users and workers of systems who do not understand it, and whom are frequently given partial or bad information. I don't think the safety measures are 'extreme and prohibitive', I think they are proportional and necessary.

A good example are our favorite Ascaris eggs. Very hard to kill all of them, treatments that want to assure 100% of Ascaris elimination will always be complicated or expensive. On the other side, Ascaris infections are far from being deadly. They become problematic only if they are extreme and widespread.
So WHO thinks the benefit of reuse (e.g. of large scale wastewater irrigation) outweights the remaining small disease burden caused by 1 Ascaris egg per g soil or L water.


I don't think the issue is only the actual infection risk of Ascaris, but the notion that Ascaris is a relatively easy pathogen to measure (which itself is problematic, given the discussions we have had here about methods) and that if one can kill Ascaris to safe levels, you have a good chance of also destorying other more difficult pathogens.

It might not be the best standard, but I'd be interested to hear a rationale for any other standard. Not having a standard is a silly solution, in my opinion.

Now, if you would require 0 Ascaris eggs in water used for irrigation, treating wastewater to that level would not be possible at reasonable costs. Thus irrigation with wastewater would need to be prohibited. It may happen then that farmers continue to irrigate illegally with raw wastwater. The final health impact of extremely strict guidelines can therefore be worse than of more pragmatic ones.


First, I don't think anyone is arguing for a 0 Ascaris ova standard, and personally I'm not making any statements about irrigation waters because I don't know anything about that side of things. But I think it is a reasonable standard for feces reuse, which we know contain a range of pathogens, some of which are difficult to isolate and measure.

Second, I think it is reasonable to expect new systems to be better than the old ones and to meet the highest standards. In fact, there is a case to be made for having more stringent standards than those which would be accepted in Western countries, given that the systems are largely unmonitored, dispersed and may well be less effective than the ideal.
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  • muench
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

Dear Joe,

Just jumping in to support what Florian has said, because I agree with him:

You said:

Florian wrote:

Well, I think there is at least as much evidence supporting the currently used recommendations.


[Joe:] I'd be interested to hear some. I don't think I've seen anything which suggests the storage recommendations are robust.


The evidence and guidelines are part of the WHO (2006) Guidelines on Reuse. Most probably you have read them (but maybe others haven't). So I thought it would pay off to repeat them here:

WHO (2006). WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater - Volume IV: Excreta and greywater use in agriculture. World Health Organization (WHO), Geneva, Switzerland.
susana.org/lang-en/library/library?view=...eitem&type=2&id=1004

Volume 4 of the Guidelines focuses exclusively on the safe use of excreta and greywater in agriculture. Recent trends in sanitation, including ecological sanitation, are driven by rapid urbanization. The momentum created by the Millennium Development Goals is resulting in dramatic changes in human waste handling and processing. New opportunities enable the use of human waste as a resource for pro-poor agricultural development, particularly in peri-urban areas. Best practice to minimize associated health risks is at the heart of this volume.


They are not so easy to understand but the most important aspect in these guidelines is the multi-barrier approach. According to this approach, treatment is only one of several possible barriers. Thus, according to the WHO Guidelines, even a treatment with relatively low performance in removing Ascaris eggs, can - under certain circumstances (i.e. when other barriers are in place)- , be OK.

And there is by the way little doubt that emptying an average UDDT is significantly less risky than emptying a pit latrine (even just in terms of access! Compare that to climbing into a pit - which is what people do! Can link you to photos if you like).
Reuse of faecal matter that has been dried for 1-2 years is also far less risky than using faecal sludge from a pit latrine that has not been dried at all. And it is a fact that this emptying and reuse of faecal sludge from pit latrines is going on all over the world, and it is very dangerous. So whilst "advanced/modern" systems (such as UDDTs with external composting as post-treatment for example) may not be perfect either, they are already a big step in the right direction - and they need to be coupled with those other barriers as per the WHO Guidelines.

But I do agree with you that one has to be cautious about making claims about safety that are too bold (see the discussion about the hot-box composting elsewhere on this forum)

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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

muench wrote:
They are not so easy to understand but the most important aspect in these guidelines is the multi-barrier approach. According to this approach, treatment is only one of several possible barriers. Thus, according to the WHO Guidelines, even a treatment with relatively low performance in removing Ascaris eggs, can - under certain circumstances (i.e. when other barriers are in place)- , be OK.


As I understand and read the guidelines and the background on how it was created, that is because there is a reduced risk from each barrier. I don't think I'm arguing anything different - reuse of sludge directly from a toilet system has few barriers. The more barriers there are, the safer it is.

And there is by the way little doubt that emptying an average UDDT is significantly less risky than emptying a pit latrine (even just in terms of access! Compare that to climbing into a pit - which is what people do! Can link you to photos if you like).


Well I agree there are different types of risk and that climbing into a pit is an unacceptable risk. Would I take a UDDT over a pit? Yes. Would I assume that the sludge itself is definitely safe to use? No.

Reuse of faecal matter that has been dried for 1-2 years is also far less risky than using faecal sludge from a pit latrine that has not been dried at all. And it is a fact that this emptying and reuse of faecal sludge from pit latrines is going on all over the world, and it is very dangerous. So whilst "advanced/modern" systems (such as UDDTs with external composting as post-treatment for example) may not be perfect either, they are already a big step in the right direction - and they need to be coupled with those other barriers as per the WHO Guidelines.


Again, it depends on the difference between 'safer' and 'safe'. I don't think the material from either can really be accepted as 'safe' even if one is safer than the other. Hence the need for a standard to assess the quality of different methods.

As far as I can see, this idea of a multi-barrier approach is not generally accepted, so on the whole sanitation interventions are used on their own. Hence we have the widespread advice that material from a ecosan toilet should be spread after a year of storage. I think the evidence is clear that without additional barriers (co-composting, specific types of reuse etc), it isn't safe. Again, I don't think I'm disagreeing with what you or Florian have said.
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  • Florian
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

joeturner wrote: Hence we have the widespread advice that material from a ecosan toilet should be spread after a year of storage. I think the evidence is clear that without additional barriers (co-composting, specific types of reuse etc), it isn't safe.


Let's take this example, assuming it's an houshold level system. Two years would be better than one, but basically already very good. All of the dangerous pathogens would clearly be eliminated, at most some of the persistent parasites (Ascaris) may remain. A few very simple additional barriers would eliminate completely any health risk:
- using gloves and shoes when handling the compost, washing hands afterwards.
- working in the the compost in soil, e.g. covering it with a layer of earth
- washing the crops well before consuming them
- taking deworming drugs from time to time

These measures make this a safe system, even allowing for partly non-compliance in some of them.

Now, haveing the choice of recommending 1-year storage and these additinonal measures, or storage plus well controlled co-composting with garden waste or 3-4 year storage, I certainly would go for the former, because it's simpler and more interesting to the family, thus more likely to succeed.

Again, this is just an exemaple of one specific situation. Different contexts would require different solutions.


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