This post here is the result of an e-mail conversation I had with David Bates (known on the forum as DrBates: forum.susana.org/forum/profile/userid-5431) about using lime in urine-diverting dry toilets (UDDTs).

David's experience in Mexico (which is however not current, his involvement ceased temporarily in 2008) was that lime is commonly used in UDDTs with the aim to reduce odour and to kill pathogens.

My experience from what I have read is that pretty much nobody else is using lime (anymore?) in UDDTs these days around the world. More common is ash, soil or compost (or in the case of Chris Canaday's experiences: compost derived from the UDDTs themselves), or to use no cover material at all (see also, of course, on Wikipedia here: en.wikipedia.org/wiki/Urine-diverting_dr...ilet#Cover_materials).

What speaks against using lime? I would say the costs and also it probably makes the product less attractive for reuse afterwards unless the soil where it is applied really needs alkalinity.

Heike Hoffmann had in the past told me about the use of lime in UDDTs in Peru which she opposed. This is work done by the NGO CENCA, we have a couple of their documents in the SuSanA library here: www.susana.org/en/resources/library?search=cenca (Heike had pointed out to me flaws in their designs, so don't think you can just copy their work).

Heike also posted about lime in UDDTs here on the forum a year ago:
forum.susana.org/forum/categories/53-fae...mit=12&start=24#9180

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.

And here is more information from David Bates about lime use in UDDTs in Mexico:

Lime is very abundant in Mexico...in my observation, it was "relatively inexpensive"....that is a middle class engineer talking. For those that can't afford the lime, we strongly encouraged ash, or generous portions of dry soil. Many men of the families participating are construction workers and very accustomed to working with lime as they use it their work everywhere to make stone walls and cobblestone pavement. I guess the ability to use quicklime in the UDDT's then is partially geographically - and culturally- based, and related to the construction aspect of their economy

www.loc.gov/today/placesinthenews/archiv...0321_ringoffire.html

geo-mexico.com/?p=8899

Am I right to say that lime use in UDDTs is pretty much a thing of the past, except for some exceptional cases maybe?

Regards,
Elisabeth