Use of lime for faecal sludge treatment? (pilot project by iDE in Cambodia and other examples)

  • joeturner
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Use of lime for faecal sludge treatment? (pilot project by iDE in Cambodia and other examples)

Note by moderator (EvM):
This thread used to be merged with the thread on latrine sales by iDE in Cambodia; it was separated on 27 June, but you may observe some overlaps:
forum.susana.org/forum/categories/142-up...ales-in-2-years#8964


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I once heard someone from MSF talk about using lime to treat sludge at risk of cholera infection in Haiti - but if I recall correctly the amounts required make this unsuitable for general use.

I am not sure what you are saying in this para:

However, hydrated lime effectively raises the pH of pit contents to a level that kills all pathogen with the exception of helminth eggs within two hours, and all pathogens including helminth eggs within pH.


but it is very unlikely that any sanitation system would kill all pathogens within 2 hours. The best you can argue is most likely that it reduces the levels of x (measured indicator pathogen) to below measurement limits within 2 hours. I am not sure what you are trying to say about helminth eggs.

I would need to be convinced about the volumes of lime you are using here and the practicalities/economics of adding that much to faecal sludge. I am not really sure it is quite as simple a solution as you are suggesting.
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

OK I have had a quick skim of your paper from the WEDC International Conference, and it says that Ascaris is inactivated when the faeces is raised to pH 12 for two weeks.

pH 12 is a long way to go for the average amount of human faeces which is normally pH 7 or less. The paper suggests that you found you needed 1.5% lime (w/v) - which seems like a strange measure to use because these are not urine diversion toilets so individual sludges will have a varied amount of faeces (and pathogens).

I'm not sure it means anything to describe something as 1.5% lime (w/v), maybe you can explain exactly what you mean by this. You say that you added 0.4g lime to 40ml of sludge, but that isn't necessarily therefore 1.5% lime - unless I am missing an important part of your analysis where you considered the density of the material. I think all you have stated here is that in every 10L of sludge you have added 100g of lime. How much lime is that per latrine per year?

Clearly there are potential problems: handling the lime (corrosive), handling the treated faeces (which if at pH 12 is potentially harmful), the cost of the lime, the system of mixing and so on.

Of course lime is a useful agricultural amendment, but at pH 12 farmers are going to need advice before spreading this on their soil.
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

Further to this, I think you are talking about a measure of Mass Concentration, which wikipedia states is incorrectly described as % m/v.

en.wikipedia.org/wiki/Mass_concentration_%28chemistry%29

I have never ever seen this used as a measure - as it is ridiculous. It is not possible to have a % of anything unless the things are dimensionless - ie m/m or v/v. We can sometimes use the fact that water has a density of 1 to simplify this, but clearly that is not something one can do with sludge, which does not have a density of 1 g/ml.

And even using your own measurements, adding 0.4g of lime to 40ml of sludge is not 1.5 "% m/v" anyway. That is 1g per 100ml, which is 10g per L, which is a "% m/v" of 1.

In some unexplained way, your study appears to have half as much lime again as that which you say you have added.
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  • christoph
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

Thanks Joe, you went quite further in thinking it over, I had just the idea that a very high pH is a mixing problem and a handling problem.

Regards
Christoph
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

JKMakowka wrote: If farmers are used to handling lime for agricultural purposes and would have put a similar amount of lime on their fields anyway, there seems to be little reason why it shouldn't be mixed with pit-latrine contents from time to time.


I agree with this, although I am far from convinced that the volume of lime we are talking about to get latrine contents to pH 12 relate to the amount that farmers are already using on their fields.

Sure, there are many technicalities and it is a relative niche target-group (slightly better off farmers, although that might be a reasonably large group in Cambodia), but it is simple enough of an intervention that people can figure out how to do it.

Now granted, this isn't nearly as an "break-through" ideas as iDE makes it look in their promotional material, nor will the pathogen reduction they have seen in small scale laboratory test materialize quite the same way in real-world application, but it isn't a bad approach at all.


I agree that it seems to have some benefits, so when I heard about it previously I was interested to find out why it was not in use on a wider scale. I can't remember whether we had this discussion on the forum. As far as I'm concerned the problem is mostly about the need to get the sludge consistently to a high pH and the amount of lime (and availablilty of the lime) to do that.

I also did a brief survey of the academic literature and found that it is not an effective treatment against all pathogens in the faecal waste - because some are more tolerant to the pH change than the others. I can do this again if anyone is interested in further discussion.
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  • PatrickBBB
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

joeturner: The numbers match up in the document now. Did you misread or did they change the paper?

I thought the paper was very interesting. All though I agree with Joe, it is too thin. Sludge was only collected from one latrine, a larger study should be conducted in order to give a good guideline. The study should be conducted with sludge of varying properties, and document the effects the treatment efficiency.

The unit used in the paper is confusing, I do though just see it as a technicality and don't really mind it being used. What is important is that strong and comprehensive guidelines can be made. I.e the guidelines should be something like amount of lime added by household size, or by amount of users.

I would also like to see other pathogens to be included in the study. All though I think it is good that Ascaris is included due to its high resistance, but it is dubious how useful breakdown of E.coli is. What would make most sense to me, would be to use the prevalent pathogens in Cambodia.

Further on I would like to join in on Christophs sentiments that it is not a real success unless the fecal sludge is managed in a sustainable manner. Saying that I would like to applaud you and iDE for your achievements and hope you see the criticism as constructive.

Good luck!

Happy learning. :)
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

PatrickBBB wrote: joeturner: The numbers match up in the document now. Did you misread or did they change the paper?


That is odd, the numbers do seem to be different. But it is also possible that my eyes deceived me yesterday.

I thought the paper was very interesting. All though I agree with Joe, it is too thin. Sludge was only collected from one latrine, a larger study should be conducted in order to give a good guideline. The study should be conducted with sludge of varying properties, and document the effects the treatment efficiency.


Agreed, particularly if they're using this study to base the management of 100,000 latrines upon.

The unit used in the paper is confusing, I do though just see it as a technicality and don't really mind it being used. What is important is that strong and comprehensive guidelines can be made. I.e the guidelines should be something like amount of lime added by household size, or by amount of users.


I think it matters because it is not clear enough what is being compared to what or how much lime to add. It appears that they are comparing the lime to the total volume of sludge (ie faeces plus water) in the latrine, rather than the total dry matter, which in my view is a major flaw of this analysis. If they are not doing this, the report needs to be more explicit in order to develop a SOP for managing the latrines.

I would also like to see other pathogens to be included in the study. All though I think it is good that Ascaris is included due to its high resistance, but it is dubious how useful breakdown of E.coli is. What would make most sense to me, would be to use the prevalent pathogens in Cambodia.


Agreed. The destruction of E.coli also cannot be used as a model to suggest that 'all pathogens are destroyed within 2 hours' either.

Further on I would like to join in on Christophs sentiments that it is not a real success unless the fecal sludge is managed in a sustainable manner. Saying that I would like to applaud you and iDE for your achievements and hope you see the criticism as constructive.

Good luck!


I don't think the idea is bad, but I am not really very impressed with the science on which it appears to be based. Simple questions do not seem to have been answered: namely how much lime would be needed per latrine and whether there is that volume of lime for sale in Cambodia.
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

Dear iDE and others,

I would like to apologize if I sound harsh – it is not my aim to diminish any achievement. I am just a bit allergic with the messages how many latrines, loos or whatever have been build when there is no clear sanitation concept for the whole sanitation chain. I have seen so many projects which state “we build xy latrines” or “we build yz septic tanks”. My first question is always – and the fecal material? Normally there is no answer and I see, there is no real answer in your case as well.

We had that discussion about lime a bit in some examples where there lime is used as a cover material for UDDT. There really high pH has been achieved and really everything is dead – so really no hygienic danger. The problem is… you would have to add lime each time after use. But this is critical in my view fo latrines

a) pure lime is not user friendly (dusty, harmful pH value for respiration) (therefore in the UDDT discussion there was the discussion of using the material from the chamber as cover material).

b) the high pH in a pit would immediately volatize the NH4 to NH3 and lead to unbearable odor.

So the option has to be that the lime is mixed with the material of the pit after cleaning out. I don´t know how the material looks like in Cambodia. Basically there are two situations,
One: Sufficient moisture allows to pump somehow, than mixing of lime is technically easier but still the question would be - when/where? Transport to a central point – mix a liquid material with lime and retransport it to agricultural use? We are talking about RURAL areas – that is not likely to happen. In my understanding the probability that each user does it is zero.

Or is the material dry (so cleaning out of the pits by hand) – in this case I see it technically impossible to mix the fecal material with the lime in a manner that gives hygienic security. You need some kind of machine to really mix it. In this case I would go directly to a LADEPA machine and do pellets without lime. Seems much more logic to me, but again we are speaking about very high investment costs for treatment.

So I fear we end up with 100.000 latrines – without proper fecal material treatment as no viable solution is there. This is my concern and I would be very happy to be wrong.

Regards

Christoph
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  • JKMakowka
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

The proposed mode of application (or the lack thereof) is also what confused me initially. Judging from a few impressions in the video linked in the article, it seems like we are dealing with single pit four-flush latrines that are seemingly emptied by flushing out the content with water (not that this is endorsed by iDE, but it is common also here in Uganda).

What happens basically is that during the rainy season water is allowed to fill the pit until it overflows and sludge is removed by mixing it with a stick and slowly diluting the sludge out of the pit. This is obviously highly unhygienic and a danger to anyone down-stream of those pits.
In rural areas it is also not uncommon that this diluted stream of pit-latrine content is diverted to fields and thus acts as fertilizer.

With a bit of guesswork, I assume the proposed mode of application is that quite a large amount of lime is added to the pit with some water and then mixed with a stick prior to flooding it with water. If sufficient time is given (and maybe there is also a heat build-up from the exothermic reaction?) this should make the effluent much safer for everyone involved (although probably not "safe").

Given that the effluent flows into flooded rice paddies, it is also more or less cost free if the lime would have been otherwise applied to the field directly.

Edit: Just to make sure: I am not saying that this is a good method or am endorsing its use ;) I am simply observing how the most likely application in a rural setting will be. However I consider this a "better than status-quo" approach.

Krischan Makowka
Microbiologist & emergency WASH specialist
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  • kckoch
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

Gentlemen,

I have forwarded your concerns to our lime team, and received the below response. The paper that was first uploaded was not the final draft, and included mistakes that were corrected in the final version. As you noticed, the correct draft has now been uploaded.

From our engineers on the lime team:

The numbers they are quoting are from the first draft of the paper (0.4 g in 40 ml was wrong, and was corrected for the final version).

1.5 % w/v is the maximum for a no-water sludge, used also by the UCB group (not yet published). Typical sludge in Cambodia has a lot more water due to flushing and washing, and thus requires even less lime. 1.5 % is the max needed for disinfecting sludge of only urine and feces, in typical ratios, with no added water. Any water added to the mix decreases the amount of lime needed to raise and maintain the pH.

The typical problem is the filling up of pits with water, from users and infiltrating rainwater. Hence our decision to treat the liquid phase of the sludge. Users need to empty frequently to deal with this water, rather than the solid sludge accumulating at the bottom of the pit, which happens at a much lower rate. Solubility of Ca(OH)2 in water is less than 0.2 g/100 ml, so while the pH is high enough to render the liquid safe, and at the same time, the high pH is expected to be attenuated by the soil relatively quickly. This is being tested.

Expressing a concentration as % w/v is acceptable, just as ppm or ppb is acceptable when w/w or w/v is indicated.
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

Thanks for that information,
Could you ask them how it is planned to guarantee that the user really will add lime in the right proportion? The way Krishan describes how it probably could be done seems to be a very dangerous way of dealing with fecal matter.
Christoph
(By the way I put the "like" to the wrong post of you, but no way to correct that – I really appreciate the open conversation so it was ment to the last post)
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Re: Press Release and infographic: iDE Cambodia hits 100,000 latrine sales in 2 years - and the power of sanitation marketing

Any water added to the mix decreases the amount of lime needed to raise and maintain the pH.


Yeah, this is explanation is not really very helpful.

What you appear to be saying is that the lime needs to be added in proportion to the faecal constituents of the latrine. So a full latrine which contains a small proportion of faeces would need lime in proportion to the weight of the faeces not the faeces+water sludge.

I am not sure this is even correct. Will the same amount of lime have the same effect on the faeces with and without extra water? Surely that depends on the pH of the water.

The typical problem is the filling up of pits with water, from users and infiltrating rainwater. Hence our decision to treat the liquid phase of the sludge. Users need to empty frequently to deal with this water, rather than the solid sludge accumulating at the bottom of the pit, which happens at a much lower rate. Solubility of Ca(OH)2 in water is less than 0.2 g/100 ml, so while the pH is high enough to render the liquid safe, and at the same time, the high pH is expected to be attenuated by the soil relatively quickly. This is being tested.


I am not sure what you mean by 'attenuated by the soil'. You are adding a liquid you say is a high pH to the soil. The effect on the soil will depend on the soil type and the soil pH. If you are adding a lot of water to the soil surface with a high pH, I suspect the main effect will be that it will run immediately into the nearest water course.

This is still not answering the question of what happens to the faecal solids.

I am not an engineer, I am a trained soil scientist. % w/v is meaningless. I am not even sure you are even using it correctly in the strange way that you are defining it. How is anyone supposed to tell how much lime to add to their latrine - given that the latrines might contain a varied amount of faecal waste and a varied amount of water?

Expressing a concentration as % w/v is acceptable, just as ppm or ppb is acceptable when w/w or w/v is indicated.


This just is not true. ppm and ppb are SI units, % w/v is not.

Anyway, leaving that to one side, I would still like to know how the users of latrines in Cambodia are to use the knowledge that a 1.5 % w/v will elevate the sludge to pH 12. In a given latrine, how much lime do they need to add per year?
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