Faecal sludge treatment in high water table sandy soils
As part of a sanitation marketing project along the east coast of Madagascar several NGOs have made significant progress on construction of family latrines using SanMark approaches. The solutions that were developed were quite innovative and effective. The implementorshave identified teams to empty latrines, invested in latrine emptying equipment, and trained the teams on faecal sludge emptying. However, the main problem still remaining is treatment of faecal sludge. The two small towns where the project is being implemented contain sandy soils with high water table (mostly 0.5-3 m below surface), thus treatment options are limited. Waste burying integrated agriculture is not an option as is used in the high plateau of the country where the water table is quite low, and there is limited budget for more expensive options like biodigestion and complex DEWATS treatment. In South Africa, LADEPA faecal sludge drying machines are promising and potentially mobile, but not financially feasible in for this project.
I have done quite a bit of research with colleagues here in South Africa, but not come up with a n ideal solution yet. I am thinking that a DEWATS designed for high water table could work, but again, cost may be an issue.
Any ideas would be greatly appreciated as this is a high priority project at the moment!
I have just had a look at the LaDePa and agree that it will not be suitable - not on economic grounds, just that it will not be technically viable in any case due to the likely content of plastics and other hard solids that will need to be screened out and the need to get to a solids content of 20-35% before the sludge can be pelletised.
There is a manual on faecal sludge management published by IWA and SANDEC which you can download here:
My first thought is that you should consider vegetated sludge beds, which are covered in the publication. These have been used successfully in Denmark and SANDEC have done some work in Africa which is encouraging. You would have to line the beds if it is necessary to prevent pollution of the ground water (but the pit latrines will be doing this anyway I assume) and you will need to treat the underdrainage. If you use ponds for this, again they would need to be lined.
The problem with the lining is that after a number of years you will have to remove the accumulated sludge and this would risk puncturing any membrane, but you should be able to design some protection to the drainage layer and membrane to minimise this risk.
We did some work with WA Bangladesh and Practical Action looking at solar sludge drying beds, and subsequently with SNV in Laos (developing a construction manual for the private sector). Some discussion of our initial work is here: https://forum.susana.org/forum/categor....
We managed to successfully treat sludge 'above ground' with final liquid effluent polishing in a reedbed before discharge to the environment.
It was designed for monsoonal, flood prone areas, so I'm sure it could be applicable in Madagascar.
Give us a shout if you'd like to know more,
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