Hi Dilip

We have done measurements of sludge accumulation in school toilets and have come to the conclusion that 10 litres of sludge per user per year is a reasonable number to use for designing your leach pits for pour flush toilets.  For domestic toilets (i.e. at the home) you need to provide about 30 litres per user per year.  If you are planning, say, a 5 year filling cycle then for that school you need 23.55 m3 space for sludge accumulation.  If you are using twin pits you can double that, or you could use smaller pits and a shorter emptying cycle.

If you want details on the sludge acumulation observations we have made, dm me at This email address is being protected from spambots. You need JavaScript enabled to view it..

Regards

Dave Still

Dear Dilip,

Thanks for the detail on the depth of the water table. This is very good.

Please answer all my questions. Are there water wells or streams anywhere near the site?

Is the idea to run the blackwater from all of the toilets to one centralized pipe and then fill one pit and then another? (Let's call the holes where we put poop pits, not wells.)

The concept of Twin-pit Pour-flush is to have 2 pits for each toilet, maybe a meter or two away. To have the pits 43 meters away would have the great risk of the pipes getting plugged. Have you calculated how many toilets you need for this number of children?

What is the terrain like? Is it flat or sloped?

The greywater from sinks and showers can be used productively. It can be put into a Vegetated Sand Filter, where grass is grown that can be fed to animals. Other productive plants could also be planted.

What organization is doing this work?

What stage is this at? What is the timeline?

Best wishes,
Chris

Hi Chris,

Thanks for your response.
The highest water level is 7mtrs during the rainy season. The well depth planned is 2,10mtrs on a dia of 1,10mtrs. So there is enough depth for the pathogens to degenerate. We plan to bore a well at at distance of 43mtrs, so that should not pose a problem. Grey water evacuation from the toilet block is also +30mtrs
Thesoil structure is characterised as follows
    - Compressed soil composed of sand and clay
•        - From 0 tot 2 m: clay
•        - From 2m tot 4 m: gravel
•        - From 4m tot 5,5 m : clay-sand
•        - From 5,5m tot 8 m: sand- clay
 
-The water table is estimated at 7mtrs during the rainy period
-The water table is estimated at 18mtrs during the dry period

Though we have foreseen sufficient toilets, we are not sure how many sets of leach pits are required.
There are 457 pupils at Kolikoli primaryschool (260 girls and 197 boys) along with 14 teachers.

Nobody seems to know. Any help on this would be greatly appreciated

Kind regards,

Dilip

Dear Dilip,

How deep is the groundwater there? Are there water wells or streams anywhere nearby? I would say that you are lucky to have a sandy/gravely layer within reach, but is that layer above or below the groundwater?

I do not understand your question. In that system, you need 2 pits per toilet. One could have more, if desired, to give more time for the excrement to decompose before digging it out when it is just soil.

Are you using SATO toilets and junctions or from other factories?

Best wishes and please let us know how things go,
Chris Canaday

We are currently working  on a humanitarian project for school children in a village in the Congo.
 
We plan to build pour flush toilets using twin leach pits.
There are 457 pupils at Kolikoli primary school (260 girls and 197 boys) along with 14 teachers.
The wells have an inner diameter of 110cm and a depth of 210 cm (including the first 30 cm sealed depth).
A depth of 210 cm is needed to penetrate the clayey topsoil and reach the sandy gravel below.
The number of toilets are according to WHO guidelines, but we are not sure on the leach pits
 
Can anyone advise us how many sets of leach pits are necessary ?
 
 
Thank you for your help,
 

Dilip Mirchandani
Rotary District 2130 (Belgium)
Tel: +32-475410943