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


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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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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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  • 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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  • 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.

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

[This is the start of Page 3 of the discussion; for earlier pages click on the square page buttons above or below.]

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

It has been mentioned before, but I think that is important from a user compliance point of view:

A high pH leads to degassing of NH3 (by facilitating the reaction from the dissolved NH4), which smells very badly.

Since we are talking about non-urine diverting toilets the amount of NH4 (a brake-down product of urea) in the pit should be quite significant, although over time (and sufficient aeration) most of it is converted to NO3 by bacteria. However this reaction could be suppressed by the high-pH (not sure).

Maybe instead of constantly added lime, it would make more sense to use it as a fecal sludge treatment at a central site?

I think Mughal's method of vacuum drying the sludge would be a good supplement to that.

What I have in mind is the following (mainly for fecal sludge management in urban areas):

After collecting the fecal sludge from emptied pit latrines, apply sufficient quantities of lime to it to reach high pH and some precipitation of sludge. The supernatant can probably be safely infiltrated, but the high CaCO3 salt content might be problematic to the aquifer in the longer run.

Then apply the concentrated sludge to a vacuum assisted sludge-drying bed but under a typical tunnel greenhouse (or just a black plastic foil cover?) so that higher temperatures from solar energy are reached and all of the smelly air has to go through the vacuum pump.

Use a cheap liquid ring vacuum pump with an acidic sealant liquid (water with cheap citric acid) to wash the NH3 out of the drying exhaust to avoid most odour nuisance (an additional air-filter might be necessary) and potentially produce some quantities of NH4 containing liquid fertilizer/irrigation water for local use.

The resulting dry sludge with most of the lime in it can then be scraped of the drying bed, pulverized and sold as combined lime, soil-supplement & fertilizer product to farms.

Due to the combined effect of the greenhouse heat, the drying period and the high pH of the lime the resulting product should be quite safe to apply on land. But of course this needs to be tested in a lab.

Due to the high lime content the resulting product should also sell for more than regular organic fertilizer and thus the costs of treatment can be partially offset.

From a sustainability point of view it has to be stated though that lime needs a lot of energy to be burned (but not quite as much as cement) and that the vacuum pump needs electric energy or fuel to run.

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.


[This is the end of Page 2 of the discussion; for later pages click on the square page buttons above or below.]
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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

Please keep in mind that our work in this area is still at an early stage. We are not making any claims of success. We are still determining ourselves what is productive information to share with others. However, we can give you an update on what we are testing, and how we are going about it. Following are two notes of clarification I have received from iDE team members. The first is from iDE's Lime Team working in Cambodia, the second is from iDE's Measurement and Evaluation team. Please consider this a general update on where we are currently in our thinking and approach. Also, thank you to F H Mughal for the helpful information that you have shared on this thread. I will be sure to forward it to our team.

From the iDE Lime Team:
The WEDC paper focuses on the results of controlled batch experiments, performed on sludge from a typical latrine. Based on the promising results from these studies, we are testing lime with a large number of household latrines, as well as looking at lime-treated sludge as a soil amendment, including the effect of the high pH on soil. This on-going work is briefly discussed in the WEDC paper. The results should start coming in in a couple of months, and will cover recommendations for lime use by households to make pit content safer, and for use of lime-treated sludge as a soil amendment, including application rates.

To clarify our usage of the notation "1.5 % w/v": 1.5 g of lime was used per 100 ml of sludge.

Addition of lime caused the solids in the sludge to precipitate. After a three-week incubation, E. coli was not detected in either the supernatant or the sediment of the lime-treated sludge, whereas both supernatant and sediment in the untreated control was positive for E. coli. Our source sludge was negative for Ascaris, and no source of Ascaris was readily available when the experiments were being set up. We are currently looking into testing efficacy of Ascaris elimination by lime.

From our Measurement and Evaluation team:
In addition to the controlled lab experiments we are going to be conducting two additional evaluations whereby we are testing user compliance rates of two competing regular application practices: 1) a weekly application of lime; and 2) per-use application of lime. In order to accurately determine the user compliance rate of these two application protocols, the evaluation controls for the amount of waste in the pit at the beginning of the evaluation period, the length of time the household had owned the latrine, starting pH level of the pit, water content of the pit and seepage rate of the pit. The multi-stage cluster sample design should allow us to estimate compliance rates with a precision of +/- 10% and a 90% confidence interval.

The second component of this evaluation pertains to the initial treatment protocol that we decide to pursue. As many of you have already noted, it is important to ensure that the existing waste is fully treated before a household begins a regularly scheduled application protocol. We are referring to this initial treatment as "the big dump protocol." We are randomly selecting a sample of latrines from Kandal province to test whether one of the competing big dump protocols is more effective than the other. The sample design should allow us to test for a 95% efficacy rate with a 90% level of significance and a precision of +/- 5%.

Once we have completed these additional evaluations we will have three valuable pieces of information to help us better understand whether or not this is a possible solution that we should be pursuing as we move forward.

If you would like additional information on the experimental designs and/or the sampling protocols please let us know and we can provide additional details.
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  • F H Mughal
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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

Use of lime is in practice for the last 100 years. Lime is used for controlling odors from fecal matter. Back in early 1960s, when I was a school boy, I used to see women in villages putting lime on child's feces. Lime, back then and even now, is dirt cheap here. The forest staff, for decades, used to apply lime paint on the tree trucks to prevent pest attack. This practice continues till today.

According to the classic USEPA 1979 publication: Process Design Manual for Sludge Treatment and Disposal, lime conditioning an anaerobically digested sludge to a pH of 10.2 to 11, and then vacuum filtering and storing the cake, destroy all odors and pathogenic enteric bacteria.

Laboratory and pilot scale work on lime stabilization showed significant reductions in pathogen populations and obnoxious odors when the sludge pH was greater than 12. Disposal of lime-stabilized domestic sludge on cropland would have no detrimental effect on plant growth and soil characteristics, the USEPA publication says.

The publication further says that lime treatment is being used to stabilize the sludge from at least 27 municipal wastewater treatment plants. Landfill burial is the most common means of disposal for lime-stabilized sludge. However, lime-treated sludge from eight of the plants in Connecticut is applied onto land.

Lime addition to sludge reduces odors and pathogen levels by creating a high pH environment hostile to biological activity. Gases containing nitrogen and sulfur that are evolved during anaerobic decomposition of organic matter are the principal source of odors in sludge. When lime is added, the microorganisms involved in this decomposition are strongly inhibited or destroyed in the highly alkaline environment.
Similarly, pathogens are inactivated or destroyed by lime addition. Three fundamental design parameters must be considered in the design of a lime stabilization system: pH, contact time, and lime dosage.

The design objective is to maintain pH above 12 for about two hours to ensure pathogen destruction, and to provide enough residual alkalinity so that the pH does not drop below 11 for several days, allowing sufficient time for disposal or use without the possibility of renewed putrefaction. The recommended design criteria for accomplishing these objectives are:

• Treat sludge in the liquid state; and

• Bring the sludge to pH 12.5 by lime addition and maintain pH above 12.5 for 30 minutes (which keeps pH >12 for two hours).

For lime dosage, the publication says that the amount of lime required to stabilize sludge is determined by the type of sludge, its chemical composition, and the solids concentration.

Lime requirement to attain pH 12 for 30 minutes for primary sludge is 0.12 lb Ca(OH)2 per lb of dry solids; for septage it is 0.2 (average lime dosage).

According to another classic publication: Handbook of Advanced Wastewater Treatment – Culp, Wesner and Culp, 1978, lime coagulation has been demonstrated to be capable of effectively removing and inactivating viruses at high pH values. The mechanism of inactivation under alkaline conditions is probably caused by denaturation of the protein coat and by disruption of the virus. In some cases complete loss of structural integrity of the virus may occur under high pH conditions.

I must admit, this discussion on use of lime rekindled my forgotten interest in the use of lime in wastewater treatment as a coagulant, and for sludge treatment. The two forms of lime used are quicklime or calcium oxide (CaO) and hydrated lime (calcium hydroxide – Ca(OH)2). Hydrated lime is the result of adding water to powdered quick lime.

I’m of the opinion that we should encourage progress that is being achieved in sanitation and, we should not be overly aggressive if some numbers don’t tally or add up quite perfectly. I’m sure, the forum’s administrators will agree with my view point.

That being said, I give credit to KC Koch (the originator of this thread) and the iDE for doing excellent work on sanitation in Cambodia – Good luck!!

F H Mughal
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