Screwing the Sludge

Warning: This report contains images of poo!

The pit sludge auger (I'll just call it the auger) is one of the two machines I've been developing for pit latrine emptying (the eVac being the other).

It's quite a simple device: a screw is turned inside a casing, turned by an electric motor on the top. This is stuck into the pit latrine and the sludge should fall out of the top, into a bucket. From there it can either be taken away in a vehicle or disposed of nearby.

The concept should yield several advantages:

  • It can be carried by 2 or 3 people, so is relatively portable.
  • It's quite cheap.
  • It can access pit latrines some distance from the road.
  • Using an electric motor means that it should be empty the pit quite fast.
  • It's simple and easy to service.

The auger was well advanced in development when I got here, and after much tinkering and testing on my pig slurry in the PiD garden, I felt it was ready to be tested out for real!

The Test

Ketha found a test site for me. About 35km outside Pietermarizburg, PiD build a pit latrine there 5 years ago. There are 18 people in the household and I'm amazed it's lasted this long.

One of the main challenges for emptying pit latrines is the rubbish that people throw into them. Without a rubbish collection it's an obvious thing to do! This tends to clog anything you use to try to empty them, and makes the pit latrine fill far faster than it otherwise would. We chiselled out the toilet seat and one of the slabs at the back of the toilet, and were pleasantly surprised that there was only minimal rubbish visible.

We set up the tripod over the back of the latrine and lowered the auger in. We switched it on and... nothing. Somehow all of the plastic bags and rags in the latrine were attracted to the screw, twisted round it and stopped anything from going up.

Brian wasn't happy at having to tell the family that the considerable hole they'd dug to empty the sludge into was not going to be filled! I intend to use the same site for eVac testing though, as it's quite convenient: so there's hope for them yet.

What I had not fully appreciated is that the rubbish isn't just in the sludge, it is actually a component part of it! There can therefore surely be no way of screening it out without screening out the sludge as well. There are only two ways I can see that the auger could ever contest with that sort of sludge:

  1. If it were at least double the diameter, then potentially the rubbish could be conveyed up. This would make the whole machine so huge that it is not a realistic option.
  2. Completely shred the waste before putting the auger in. A tough task, but possible? Ideas welcome.

At the moment the eVac seems like a more promising solution, with somebody using a long hook to get rid of the plastic. On the other hand, other countries are known to not put rubbish down the pit like they do in South Africa. Maybe there is hope yet?

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Jack8:25 pm
24th November 2011
Surely the rubbish is clinging to the mud that then gets uplifted by the auger. So what if you either add a bit or water to the the point of auger and the sludge, reducing the clinginess of the rubbish but still being able to lift the waste. Or add a bit of fairy liquid equivalent to break down clumps of the waste thus preventing the rubbish to cling to it. Or maybe I am way off! p.s i entered my website but it says it isnt valid! so im putting it here.
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