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


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

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Hi to all,
I put my personal opinion about the aspects mentioned by Elisabeth (lime use in UD toilets in Peru), I do not have own experience of dealing with lime, but we did carry out in Peru experiments concerning inactivation methods of pathogens in UD material and the specifc effects to soil conditions (incl. plant/corn growth).

1. In Peru lime use didn’t work out in UD-toilets :

- Case 1: People used a lot of lime (“the more the better”), the result was a “fecal rock” in the vault, which only could be removed with pickaxe (an idea was to grind it and REUSE as dry material in the UD toilet; in my opinion it was not a good idea).

- Case 2: When all (given) lime was consumed, people did not buy new lime, because it was too complicated to use it or to get it, or too expensive or not important enough to do it.

2. About lime use in Pit-Latrines: If people really would use lime properly (after each use or weekly) it would dry out the FS in the pit. Will that not cause removal problems? I think we agree about the fact that it is impossible to guarantee for pit latrines safe FS Management by USER. FS needs a service model OR filled Pits have to be sealed.

3. Lime in centralized FS treatment (service model): could be a possibility, but the product is a fertilizer (N;P;K) and not a soil conditioner (structure material, reduce water loss in soil). In our experience all WHO treatment recommendation for fecal material as: i) alkaline treatment pH >9/>6 month; ii) heat composting <50°C/>1 week and iii) incineration; affect the characteristics as soil conditioner; but certainly hygenization IS the most important point for reuse, especially in warmer climates.

(As the theme was separated by the moderator, I will post my opinion about the Cambodia latrine project in the other thread: )

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

Not sure if already mentioned, but this book recently linked by Florian also has a section on lime treatment (page 110pp). It mentions some additional studies and results from a pilot in the Philippines.
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  • joeturner
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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:
Overall it seems quite feasible, not too expensive and only using off-the-shelf components. I doubt however that it can be economically run just though the sale of the fertilizer products.


I can believe community scale lime treatment could be feasible. The beneficial effect of a pH 12 (or whatever it ended up being) material would depend on the soil on which it was being added. Liming is a common agricultural activity, but ideally it would only be added under supervision as it can also have negative impacts when added in the wrong places.

I suppose the question is the value added to the lime and the value added to the faecal waste by treating it in this way. How would they be more beneficial to a farmer than sold (given etc) seperately? There are various different treatment systems which could work in a controlled and managed community-scale site, why would you choose lime treatment - unless you were specifically trying to destroy something like cholera? Unless you happen to be somewhere next to a source of lime, I can't see that this would have many benefits.
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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

Hmm, yes only makes sense where there is a relatively cheap and reliable supply of lime.

I see mainly safety of handling benefits all along the treatment chain, even though of course the lime is also somewhat hazardous (but less than the pathogens in most cases).

The coagulation effect it has is also interesting, and the supernatant water is probably safe to discard without further treatment (the tougher pathogens like helminith eggs should settle with the sludge for the most part).

In the above mentioned case study from the Philippines they also suggest that it could be added near the source to allow it to settle there already. Potentially this could have the big advantage that you need to transport less sludge volume back to your treatment site. Usually transport is one of the most expensive parts of a semi-centralized treatment chain.

Last but not least, the resulting fertilizer product should be much safer to handle by the farmers even when the overall production process might have control and safety check deficits (as likely in a developing country context). It might also be easier to convince farmers to buy this "dark lime" than dried fecal sludge alone, especially if they would have bought regular lime otherwise.
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  • Dave
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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

There is a school of thought in South Africa that advocates the addition of lime to faecal sludge if it is disposed of by on-site burial (which is the cheapest, simplest and most practical method for disposing of it). I have done some reading around that to try to understand what possible reason there could be for such a practice. This is what I have learned so far:

Firstly, we use the term "lime" but what do we mean? There is quicklime (CaO), hydrated or slaked lime Ca(OH)2, limestone / agricultural lime (sedimentary rock that is predominantly composed of calcium bearing carbonate minerals calcite (calcium carbonate with the chemical formula CaCO3) or dolomite (calcium –magnesium carbonate with the chemical formula CaMg(CO3)2).

The addition of quicklime to WWTW sludge is practiced in some high tech applications. When CaO is mixed with water you get an exothermic reaction, and with enough of it (like 20% relative to the sludge) you will get high enough temperatures for long enough to kill all the pathogens, and the end result will be a lime rich sludge that could be used to both lime and fertilise fields in one go. It would therefore be given or sold to farmers who need to lime their fields - but not for general usage.

Incidentally quicklime has at times and places been used to "sanitize" shallow graves. The reason people used it was because it arrests putrefaction and thus reduces odours. However, in so doing it's interfering with the natural decomposition process so a corpse buried in quicklime will in fact remain relatively well preserved, while one simply buried in the soil will thoroughly decompose, all other things being equal.

Adding enough hydrated lime or agricultural lime to sludge will raise the pH. I guess if you add enough you will get the pH so high that perhaps you will kill all the pathogens, but how much will you have to add and how thoroughly will you have to mix the sludge for that to work, and how would you ensure that it is all done properly, and what will it all cost?

A much simpler way to kill the pathogens is simply to bury the sludge in the soil without any lime. Soil is the most complex ecosystem known to science and contains all sorts of biota that are uniquely adapted to breaking things down. Most pathogens do not move far in soil, if at all. From research we have conducted even the hardiest pathogens (using Ascaris as a marker) will be dead after three years. Plant a tree or trees over the sludge, and that way you will derive some benefit from the nutrients without putting anyone at risk.

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  • pkjha
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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 All
Use of lime in pit toilets and septage management is being discussed/ recommended for killing pathogens in some recently released books/studies. Bacterial pathogens - mostly hydrolytic in nature- help degrade human wastes till they are stabilized in the form of manure.
By putting lime in pits and raising pH to 12, all pathogens will be eliminated and there would be no /little chance of degradation /stabilization of human wastes. Consequently total volume of wastes in a toilet pit would remain more or less unchanged, causing frequent filling of pits.
In case of septage management (from septic tanks)one may face same problem. Septage effluent, after sand filter or so, may have high pH. Consequently its biological treatment would be a great challenge.
Septage management has dual purpose- stabilisation of septage and killing of pathogens for its safe reuse. Application of lime can solve the second objective and not the first.
It may be suggested to use lime, if required, to kill pathogens after the human waste is fully degraded. However, precaution needs to be taken when such degraded human waste is used as manure in agriculture land as it may affect soil pH. Further, its socio-economic sustainability by the targeted community should also be taken into consideration.

Pawan Jha
Foundation for Environment and Sanitation
Mahavir Enclave
New Delhi 110045, India
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  • denniskl
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Re: Use of lime for faecal sludge treatment? (pilot project by iDE in Cambodia and other examples)


RE removal and disposal of faecal sludge

Not sure if this or the other thread is the most appropriate for this question (which was previously asked by Christophe I believe but I didn't see an answer) - what about the faecal sludge? (By the way, I am leaving the whole lime issue out of this question, as I am less of an expert on that subject than anybody here I think)

Maybe Blake can provide a simple overview of how the faecal sludge removal and disposal is managed across the 100,000 toilets and how that can be scaled up for even larger uptakes?

I watched the videos of the marketing programme (or maybe that was Watershed but anyway), great success in uptake it seems, but what does happen with the sludge?

Is it household emptying and disposal (how and where?) or centralised service providers?or how?

I saw some reports in Ghana or Uganda where they were trialling sludge management practices which may be suitable for trial (also saw some reports from India where toilets / latrines installed were not being used because effective sludge removal had NOT been implemented so whole project was a bust).

Can you advise re this please Blake?
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Re: Use of lime for faecal sludge treatment? (pilot project by iDE in Cambodia and other examples)

Hi Dennis

Currently sludge is being managed by households. This usually results in two practices. 1 - the unhygienic emptying of pits with buckets (as is the norm throughout the large majority of rural communities in Africa and Asia). 2 - use of two pits per latrine, enabling households to alternate to the second pit when the first becomes full. This is a 'better' option as the sludge can become safe to handle after a pit is sealed for a certain amount of time. However, its complicated as the amount of time depends on consistency of the sludge, presence of flooding, fully sealed pit or not, etc.

Neither of these are good enough solutions for managing fecal sludge in rural areas. iDE takes a market based approach to all our work, and the reality is simply that nobody has figured out FSM in a rural context - especially in terms of developing a viable business model around this service. Here is a great (but lengthy) report from Hystra looking at the Sanitation sector ( ). Among other things they found that "Today, there exists no financially sustainable business model that offers pit emptying services in rural areas. There are, however, technical workarounds such as double and off-flow pits." (Pg 35). Its really a great report to understand the complexity and challenges of dealing with FSM in rural areas.

iDE is exploring (just a pilot project) using lime to treat fecal sludge, to make current pit emptying practices more hygienic. This effort is still underway, so no results to mention yet.

I think the WASH sector as a whole is finally waking up to the importance of FSM. We are seeing some possible solutions in urban areas, although these are still not profitable (as far as I know). We have seen little/no progress in rural areas with FSM. The largest remaining challenge we have in my mind.

Note by moderators: This post was made by a former user with the login name BlakeMcK who is no longer a member of this discussion forum.
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  • ben
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Re: Use of lime for faecal sludge treatment? (pilot project by iDE in Cambodia and other examples)

Dear All,

Here's publication from Watershed on :
Rural Consumer Sanitation Adoption Study
An analysis of rural consumers in the emerging sanitation market in Cambodia

They stated p12 :
Knowledge and practice around safe pit emptying must be addressed.
When asked what their household planned to do when the latrine pit becomes full, about 40% of installed adopters indicated they would have someone in their family manually empty the pit, 29% indicated they planned to hire someone to empty the pit with a mechanical pump, and 22% stated they would hire someone to empty it manually. Most installed adopters plan to spread the pit contents directly on their field as fertilizer.


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