Plastic blocks to line a pit?

  • SharedSaniMsc
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  • Rob Pickersgill
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Plastic blocks to line a pit?

Hi all,
I've been chewing over something for a few years now. Is anyone using PVC to line pits?
As I understand it, in wet pit latrines and wells, the pit must be lined to prevent groundwater seeping into the pit (and in some cases, pathogens getting out). This tends to be done using bricks and mortar, which takes a few days and a lot of effort to build up from the base. Why not develop large interlocking hollow plastic blocks, like Lego, to line pits? Could you go all the way and use a PVC slab. It would remove the need for mortar (and water), so it would speed up the process, would potentially be more impermeable, and would be much lighter than bricks, so it would only take 1 or 2 labourers. With plastic becoming more readily available, and each block taking the place of ~30 bricks, cement and water, I doubt it's much more expensive - especially if this kind of thing can be mass produced. Furthermore, in disaster relief, time really is money, so it could mean that you could set up latrines basically as fast as you can dig the pits for them.
Is it a good idea, or does it put the "no" in innovation? There might be something glaringly wrong with this; but as my username suggests, I am but a lowly MSc student, so go easy on me!
Thanks,
Rob


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  • muench
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Re: Plastic blocks to line a pit?

Dear Rob,

Welcome to the Forum! I promise I will go easy on you (don't I go easy on everyone? ;) ). And there is nothing lowly about being an MSc student, YOU are the future of innovations in WASH! B)

As you mentioned "lego" it reminded me of a previous Gates Foundation funded project, see here:
www.susana.org/en/resources/projects/details/72
Or directly here on the forum: forum.susana.org/forum/categories/106-us...-brazil-and-ethiopia

It was 5 years ago, not sure if it went anywhere but they seem to have had a similar idea:
"Lego-like bricks made of bio-composites for pit latrines"
Perhaps do a Google search to see if they published anything on it.

Regarding what you said here:

the pit must be lined to prevent groundwater seeping into the pit (and in some cases, pathogens getting out)


No, the lining doesn't really "seal" the pit, it just provides structural support to the hole. If there is groundwater, it will seep in and pathogens certainly do get out. Hence the problem of well contamination if the well is too close to the pit latrine.

If you're thinking of a fully sealed pit then that's different (and needs to be emptied far more often than a conventional pit, which is designed to let liquids seep into the ground). But perhaps I misunderstood you.

Regards,
Elisabeth

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  • Marijn Zandee
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Re: Plastic blocks to line a pit?

Dear Rob,

In and off itself a system of interlocking plastic bricks is not such a crazy idea. Though, as Elisabeth points out, the wall of a latrine pit are deliberately water permeable. This could obviously easily be designed into the system.

Remains the question of material choice. I would argue strongly against PVC, as the material is an ecological disaster. Both in production and when burning it Dioxins are released. Dioxins are a known human carcinogenic and extremely persistent in the environment (on the scale of thousands of years).

One interesting option would be to look at recycling of plastics. A mixture of PET and HPDE plastic wastes could probably produce the kind of blocks you have in mind. To the best of my knowledge, one of the main roadblocks to more recycling (especially in most of Africa) is the lack of a market for the waste that can be separated and collected. Which still leaves a question of whether we should encourage people to bury there plastic blocks all over the world?

It would be interesting to do a study about what material would have the best ecological and climate impacts. My guess is that a system of rammed earth bricks (or rings?) could be the winner.

Regards

Marijn

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  • JKMakowka
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Re: Plastic blocks to line a pit?

As plastic is a rather versatile material you don't really need to do it with bricks, but rather have some sort of sheets. This is available as a product for emergency pit-latrine construction such as:
www.evenproducts.co.uk/humanitarian-aid/latrines/pit-liner/
But more commonly some plastic water-tank are adapted for the same purpose. There are also hand-dug well liners made from plastic that pretty much serve the same purpose and can thus be used:
www.crestanks.co.ug/product/permawell/

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  • goeco
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Re: Plastic blocks to line a pit?

A number of years ago a NZ inventor developed something called the ByFusion machine which used waste plastic and made lego-style building blocks. The patent was bought out by some Americans who are looking at recycling the huge volumes of mixed waste plastic accumulating in the oceans. The thing is any mixed plastic can be reused for making blocks, so once the technology is available at a local scale this sort of thing could happen. Better than plastic accumulating in landfills and better than burning it for fuel, because the blocks are essentially hydrocarbon "sinks".

Not sure why anyone would dig a pit in this day and age though, there are better and cheaper methods and technologies available. Perhaps they just don't know better.

cheers
Dean

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
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