Removing Trash - Pit Latrine in Rwanda

[Nicolag]

We have a team emptying pit latrines/septic tanks in Kigali, Rwanda. These pits are often full of trash, which really mucks up our emptying procedure for sludge. It often comprises of 10-15% of total volume we remove. Pits are 5m plus deep and typical trash comprises of nappies, bottles, rags.

http://files.engineering.com/getfil...c945-406d-9c5e-9b22e8ef334d&file=IMG_1333.JPG

http://files.engineering.com/getfil...1fa8-44fb-869d-3cb73d7b5de7&file=IMG_1335.JPG

We currently have a 2m pole with a 1.5m extension. It is 1/2 inch hollow metal (but still quite heavy and awkward as it is 3.5m) with some bent hooks at the end. The primary issues we have are

(a) Nature of hook allows for capturing only trash which is ‘hookable’ on the spikes; plastic is left behind, often as a floating layer which displeases the customer

(b) The extension is extremely difficult to use. We’ve tried 2 types of connections – (i) an overlap of the poles with a pin inserted and removed to make the connection; (ii) mounting a bolt on one end of the pipe and a bolt on the other. This connection experiences significant stress when trying to reach a couple of kgs of waste at the bottom of a latrine.

(c) the whole process is filthy for the operator.

Options we have
1. Optimise this current hook
a. Lightweight system capable of reaching up to 3,or ideally 4m while also being easy to remove from the typical pit latrine ‘house’of height 1.5m - the connection is key here (if extensions are the only way forward)
b. Must reach deep but be easy to remove considering the 1.5m roof height.
c. Can remove plastic as well as cloths etc.

2. Completely rethink how we remove trash

The attached video and photos show the current hook, and the kind of trash we leave behind. All thoughts very welcome. This trash removal is as important as our pumping mechanism itself so we are very willing to spend money and try to upgrade to a much better solution.

Some colleagues in Uganda were working toward something like this, but it is still a long way off what we want:

https://www.youtube.com/watch?v=v-F9L7UGAKs

 

[KENAT]

Can your various refuses be categorized into 2 classes:

1) "Heavy/Dense" - sink to the bottom, put significant load on extraction tool.
2) "Light/low density" - float on top of the pit.

If above is true then you could consider having 2 different heads for your tool. For the floating stuff a heavy duty pool skimmer type design with geometry tweaked for reaching down a deep hole might work.

Rather than a simple hook would a head shaped like a garden claw but tweaked a bit work? Essentially use a rotary motion to gather stuff up around the tines. You'd need to changer the geometry some - maybe more of a 'hook' shape.

As for pole material & couplings, you could look at the shafts used on branch trimmers/tree pruner for inspiration.

http://www.americantreeservicesupply.com/product/ATSS200913PSS30?gclid=CMm1gvrl680CFZSGfgodQHsJQQ

(first google hit, not necessarily best option).



Also, could you fit a suitable cage/filter to the end of your hose to reduce likelihood of sucking up these rags etc. If just the rags etc. were left in the bottom does that make them easier to retrieve as you can see them clearer?

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[Nicolag]

Very interesting

Yes perhaps we should have a 'scooper' and (dare I say) a 'hooker'.

I too think we need to move to some kind of hook that we rotate a bit so that each time we send it down it's more worth the effort. Each time we put it down now, we get a rag or two back..but at least we should recognise that putting it down and lifting it back up is a lot of hassle so we should make the most of it when it goes down there and pull up what we can. Thanks for that.

Though, with rotation, comes hassle, here is a recent video of taking a rag from our hook:

https://www.youtube.com/watch?v=RWP9-pT5bQc

I like the look of the poles. My concern with similar systems has been in considering the joints getting covered in sludge and corroded, and just being generally difficult to operate under those conditions. But I should think again. We also wondered if it was so light would we easily snap it with say 5kg of waste hanging off the end and being roughed around in a pretty extreme (and careless) work environment (needs to be removed from the pit back up through an approx 150mmx150mm hole and gets banged quite a bit on the way through).

BUT thanks for the reminder to look to other industries that involve a bit of reaching- i wonder does anyone need to do something similar in a liquid....

 

[KENAT]

Pool skimmers work in water, though I suspect the load would be a bit too much and not sure they're typically long enough.

For the collection of floating debris, a net may work too rather than the typical flat mesh on pool skimmers I had.

In fact maybe the right net or basket set up is the way to go - though I fear it may scoop up too much solid waste.

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[capnhook]

This may seem like an idea that is way-too-far-out-of-the-box, but this is the shape of hook you need....

http://www.bbqhooks.com/ezhook.html

Study this simple design and scale it up to your use. It would be perfect for what you are trying to do.


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[Compositepro]

A bucket on a rope will bring up sludge and trash together. If you must leave the sludge behind use a wire basket instead of a bucket.

 

[Nicolag]

Some additional constraints are that we need to fit the design through the entrance to the latrine - typically a 0.2 x 0.1 m hole in a thick concrete slab. So that makes buckets etc difficult - unless we decide to break the slabs a bit more.

The bucket, or anything similar is also likely to sit on the top of layer of the latrine waste - there is a properly dense waste layer so it would need some assistance to get through - definitely something to poke it; so we come back to needing something long that we can stick down there.

Its this poking or maneuvering stick that I see as the biggest challenge - how can we make something that goes 4m down in the pit, yet can be pulled up with relative ease to remove the sludge on the end. You can imagine pulling the current system back out of a pit given the small latrine buildings and setting is very difficult and dirty.

Nicola

 

[dhengr]

Nicolag:
Could you put a 4"x4" hole in the tin roof, right over the hole in the floor slab? That way you could push the full length pipe up through the roof on entering the building, then down through the hole in the floor. You would probably not have to take the pipe apart or manipulate it laterally every time you lift it, other than pull it straight up through the roof hole. Could you then use a light suction or vacuum system on the pipe for grabbing stuff? The end of the pipe might be some sort of a suction cup/cone (small inverted funnel shape) which would pick up rags, or plastic bottles, small flat trash, etc., and hold it on the end of the pipe during lifting. The operator might have a vacuum hose valve on his belt so he could control the level of the vacuum, sufficient to hold a bottle on the pipe end, but also prevent a rag from being sucked up the pipe. The suction hose would go into a 5gal. bucket (with top) acting as something of a sump for anything which was sucked up the pipe and hose. Then a second suction hose would go out the other side of the bucket to the vacuum pump.

Alternatively, I think you should just suck everything out of those pits for disposal, each time you visit the site, instead of just trying to remove hard trash. They do have to be pumped out periodically, don’t they? Use a 3" hose with a small grinder on the business end of the hose, for rags, plastic bottles, etc.; grinding everything into small enough pieces so a sewerage suction pump (septic tank pumping equipment) can handle it. We don’t have to deal with the plastic trash, etc. but we pump septic tanks all the time here in the USA. This waste goes into a tank truck which has the suction pumping equipment on it, and is then spread in fallow fields or put into city disposal systems for disposal.

 

[Nicolag]

Thanks for the feedback Dhengr and apologies for the slow response. So I should have mentioned, we are actually emptying the latrines completely - we just try to do some pre-removal of rags etc because they block our pump (we currently use a vacuum based system) - create vacuum in small barrel by side of pit, suck in sludge (full thread here:

http://www.eng-tips.com/viewthread.cfm?qid=408959)

Maybe we should look at how practical removing the roof is - in many instances it would save us quite a bit of time and may not actually be that difficult. We will start to add this to our pre evaluation assessments.

As for the grinder, some groups have tried to develop systems like this but without success. We have a high proportion of rags which I think tend to be hard to chop up....but again, perhaps I should also revisit the reality of this. We typically only have a 0.2 x0.2m access hole to the pit which is quite restrictive in terms of what we can get in there....but if we had a really good device, i'm sure it would be worth breaking the slab for.