Emptying pit latrines in particularly steep areas - seeking advice on
transport of sludge
We are currently emptying pit latrines in Kigali Rwanda with moderate success using an eVac and Gulper. We had a vision for transfer stations across the city but some of the areas are so steep that the effective areas for the transfer stations are truly minimal...as a result we're having to park a truck roadside and carry sludge in 25kg lots to the truck. Thats 100 barrels for the average 2.5 tonnes we remove. Average distance to the road of about 300/400m but a vertical drop or climb of 100/200m. Very steep - not a great job, lots of laborers necessary.
Any got a better idea? I imagine the only alternative is a long pipeline but I don't know the limits of pumps well. I imagine boosting from the pit side is easier, but bear in mind access to pit is so poor - whatever we bring there, we need to be able to carry. Can we suck from the truck end? What are the typical 'sucking' limits on tankers and how might I enhance that?
We're prepared to absorb the capital costs, so we can afford to spend some money, but we would like operational costs to remain at a level the customer can afford (~$50)
There was a project to compare pit emptying equipment in Botswana. This was long before the development of any of the current human powered systems but I ttink that one system that was tried has a potential for further development. This was a system for filling drums with sludge remotely from the main tanker. The trial report can be found at: https://www.ircwash.org/sites/default/...
A development of the remote system is possible where the small tank taken to the latrine site is both filled and emptied using the vacuum pump mounted on a road tanker. This is a standard technique used when desludging oil tanks and the like. The mobile tank is connected to the main tanker by an air hose as well as a sludge hose. The remote tank is filled by a hose connected to the top of the tank and extending into the pit using the vacuum via the air hose from from the tanker which would be parked as close as possible. Then the sludge can be transferred to the road tanker by reversing the air flow in the hose to the remote tank, closing a valve on the suction hase from the pit and opening a valve at the bottom of the remote tank and forcing the sludge through the hose to the main tanker by air pressure. This is not limited by atmospheric pressure and the driving air pressure can be a considerably higher and so the sludge can be transported further or raised higher than using a vacuum. The process would need to be repeated as many times as necessary, but the main advantage would be that the remote tank would be empty both when being taken to the pit and when brought back to the road, but the amount of hose required would be considerable and the vacuum pump would need to be quite powerful to overcome friction in long hoses. For long distances it would be possible to have more than one remote tank, but this would add even more complexity to the system.
While this is not going to be a cheap system and would take quite a bit of development (there were a number of problems with the far simpler system that was trialed in Botswana), but I can see no other alternative to manhandling drums of sludge up and down the slopes. I can only wish you luck if you do decide to pursue this approach.
Generally speaking the vertical suction lift of a vacuum tanker can not be more than 3-4 meters (top of tank to bottom of pit/septic-tank). There is a hard physical limit of <10m (due to atmospheric pressure), but practically for sucking sludge 3-4m is really stressing it already.
What is not quite clear from your post is if those 100-200 meter vertical distance are above or below the road. If above, one can probably come up with some gravity driven large diameter piping scheme (like a temporary 4-6" sewer using PVC pipes)?
If below, if would probably be a better idea to find another collection point further below, as pumping sludge that high is very difficult & needs expensive equippment.
Edit: how about installing a small cargo only rope-way in these communities (to transport the barrels)? I am sure that would be also appreciated for may other materials (heavy cement bags for example). You can probably operate it with a electric winch running of a car battery.
Temporary or permanent pipeline - if you're going downhill...
The challenge may be that in low income areas, the access is also "crooked" - so the route will have to go round corners.
You may be able to use any surface water drains if they are lined - as long as you can capture the waste at the down hill end
The sludge will need extra water to make it more mobile, which may require more tanker journeys
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