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: 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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  • Florian
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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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  • joeturner
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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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  • muench
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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:

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  • Florian
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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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  • joeturner
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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?

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?

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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  • 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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  • Marijn Zandee
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Re: Level of tolerable risk in a reuse context?

Dear all,

To start parts of the discussion above reminded me of one we had last year: reuse of feacal matter is it worh the cost.....

Further, I do find the acceptable risk discussion interesting, I think that also in the "west" there are large differences in approach. Thinking of the more litigious society in the USA, where there the culture is becoming more and more that we should guarantee a "risk free" life (even if this is impossible). Where as in Europe it seems risks are, at least for now, still more accepted. The differences in the way the debates about ways of dealing with nuclear waste went (and the results) between the USA and Sweden are very instructive in this respect. Forgive me this tangent, but it is Saturday morning and it does actually build a bit of a bridge to the rest of my post below.

If we are to consider that from a point of risks that the re-use of fecal waste/sludge without advanced secondary treatment is not acceptable then we can also re-frame this as: What do we do with this "hazardous waste"?
I think that if we look at the question from this angle we also find a strong argument for the use of ecosan style technologies. Because dry/low flush, composting or dehydrating solutions actually minimize the volume of this waste that we would now consider hazardous and needs treatment/storage.

And as Florian also points out the world is complex. For instance in a rural setting how many of the worm infections that people have are from exposure to human excreta and how many from animal dung? This does not mean for me that we can neglect the problem of exposure to worm infections from human excreta, but that we should also de-worm livestock if we de-worm people.

As I see it now, there are a number of re-use oriented toilet solutions, that as a result of various processes reduce the exposure of people to bacterial and viral pathogens. This is a huge step forward, especially if a community did not have improved sanitation before. This does leave the question of how to deal with the helminth issue in a way that is economically, socially and technically viable and sustainable? I think this is again where the multi-barrier approach kicks in and where there needs to be a recognition that the (peri)urban and the rural settings are very different.

I do not have the answer a to the question above, but I would like to list some observations and statements that I have picked up from various texts and discussions here:

1.) Composting is only going to work in batches that are relatively large and well supervised / managed. This requires a collection and management system and is thus only viable in (peri)urban settings.

2.) At household level, in rural area's, the amount of fecal waste/compost from a low or non flush toilet is quite limited. Therefore I would suggest that some form of re-use in planting trees (>20 meters away from water sources) is a feasible strategy. It would require people to plant 1 or 2 trees per year and should isolate the worm ova from the food chain.

3.) Especially in rural area's, a multi-year de-worming campaign for both humans and animals is likely to increase the impact of a sanitation intervention.

4.) Training, tools and protective clothing should be provided as part of a sanitation intervention that does require handling of fecal waste / sludge (practically speaking, every intervention).

Kind regards

Marijn

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