Level of tolerable risk in a reuse context?

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

I am not so sure any more what exactly we are discussing about?

joeturner wrote: The systems should get to <1 ova per g. Barriers reduce the risk, but toilet waste should be treated, the other barriers are not enough.


Yes, WHO says 1 Asc. egg/g should be achieved and yes, waste needs to be treated to achieve this. Did you get the impression I argue against this?

Storage is just one of many available treatment options.

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

Florian wrote: Have a look at the second video, between 13.08-14.23, then you may understand better the point I tried to make above.


And chapters 4 and 5 of the WHO standard. The systems should get to <1 ova per g. Barriers reduce the risk, but toilet waste should be treated, the other barriers are not enough. Table 5.3, Table 4.3, and text in section 4.4.2.

Operational health protection measures include agricultural use practices and the preceding treatment and transport. Even if a treatment is validated and verification monitoring has done, process steps or handling practices may occasionally malfunction resulting in a fertilizer product that is not completely safe. Therefore additional measures should be taken in order to further minimise the risk for disease transmission


We are talking about systems that have not been verified and are not routinely measured. Storage should reduce pathogens to safe levels, but without additional treatment the risk is too high. Therefore it is perfectly reasonable to have additional treatment or extra barriers such as storage or reuse restrictions.

If you have a new system, it is perfectly sensible to have to show the <1 ova per g, and ideally you'd be showing that for every new installation and with regular batch monitoring. If you don't know how the system is performing or you don't know where the sludge is being used, then you don't know how reliable the barriers are.

And this is all based on risks from pathogens we do know something about. I think there is good reason to agree with Ralf that the advice should be even more conservative than this.

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

Hi Joe, I had now a quick look through the youtube videos you posted. Thanks a lot for posting them, very nice again, these presentations by Mara. In particular the second one shows how math can be put to the multi-barrier concept...

Have a look at the second video, between 13.08-14.23, then you may understand better the point I tried to make above.

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

muench wrote: Joe wrote:

My reaction: there is actually no such thing as "safe". Only "sufficiently safe" or "acceptably safe".
Same with sustainable. Nothing is 100% sustainable. One thing or process may be more sustainable than the other.

There is a German saying which comes to mind: "Life is risky and at the end you die!" :evil:


Again, I'd say that is the purpose of having a health-based risk assessment recommendation. If there is a different standard of safety that should be used, then fair enough, but any standard is better than no standard. As far as I am concerned, the risks associated with toilets without secondard treatment are too high, I don't think they reliably meet any standard anywhere. I appreciate the risks can be reduced, but I don't believe the reduced risk is safe, hence I would not advise it. I don't think it is ever unrealistic to expect a system to get <1 helminth ova. That system might include various other barriers, I accept that. But without secondary treatment they might be safe or they might not. In my view, that isn't good enough. Hence the need to be conservative and to assume the material is unsafe.

Florian wrote: Of course you are correct with this, my formulation above was too simplistic. Impossible to eliminate any risk, its always about bringing down the risk to a level that is agreed on to be acceptable.


Agreed, and the acceptable measured level is the <1 ova Ascaris measure. Happy to hear of any other measures and standards as I said. In a circumstance where you cannot be sure (because you are not measuring pathogens), you have to make a conservative assumption and build in a lot of extra barriers.

Joe, as you say we agree more than we disagree. I just think that with your almost exclusive focus on treatment and quality of treated products, you are too much negelecting the other relevant dimensions.


I don't accept that there is anything more important than ensuring treated toilet waste is safe. If that means admitting we can't be sure and advising that the material be used in conservative ways, so be it. I think there is plenty of evidence to suggest that is a sensible way to work.

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

joeturner wrote: I'd be very hestiant in ever saying that all health risks have been eliminated. They are certainly reduced doing this, they are further reduced by co-composting and other treatment. Even there, it still might not reach the full definition of safe 100% of the time.


Of course you are correct with this, my formulation above was too simplistic. Impossible to eliminate any risk, its always about bringing down the risk to a level that is agreed on to be acceptable.

Joe, as you say we agree more than we disagree. I just think that with your almost exclusive focus on treatment and quality of treated products, you are too much negelecting the other relevant dimensions.

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

Joe wrote:

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.


My reaction: there is actually no such thing as "safe". Only "sufficiently safe" or "acceptably safe".
Same with sustainable. Nothing is 100% sustainable. One thing or process may be more sustainable than the other.

There is a German saying which comes to mind: "Life is risky and at the end you die!" :evil:

(P.S. in my role as moderator I will move the last few posts away from the TPS thread later on today because they are not specifically on TPS anymore)
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

Florian wrote:
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.


Well, we don't know that in an individual situation, and that is the problem. If the thing works properly, that should happen. The risk is that if we are not measuring pathogens, there might be retention of the pathogens. We know this can happen.

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


Again, all good advice, but we don't know that would eliminate any health risk. In fact, I think that without additional treatment, there as still risks. If Ralf is correct in what he says, there may even be health risks we do not fully understand at the moment.

I'd be very hestiant in ever saying that all health risks have been eliminated. They are certainly reduced doing this, they are further reduced by co-composting and other treatment. Even there, it still might not reach the full definition of safe 100% of the time. In fact the recommendations recognise this, and the way that the microbial risk has been assessed is with a Monte Carlo analysis which randomly assigns different conditions to give a range of outcomes.

This is a video explaining the QMRA that was used to calculate the WHO recommendations:

youtube vid

edit more here

vid

For a more on the Monte Carlo assessment, see here from the University of Leeds
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Re: What is Terra Preta Sanitation (TPS) all about? Hype or ingenious?

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


Easier to explain how to do it, easier to do. I don't think co-composting on household level should be used for hygienisation treatment. Difficult to make sure that the whole heap gets hot enough for long enough time. Storage is certainly more robust.

On large-scale level, where the process is managed by professional staff, that may be different of course.

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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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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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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?

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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