Emptying septic tanks/pit latrines in Kigali - Rwanda 3

[Nicolag]

Hello

I am an engineer working in Kigali to design systems for emptying pit toilets. Some key facts:
- 90% of Kigali (1 million people) have no sewer
- Instead of a sewer, people have 'on-site' sanitation - either a septic tank or pit latrine (basically a 2-5 m deep pit in the ground that you squat over)
- Many of these pits are not accessible by road, Kigali is incredibly hilly, and the more informal areas are extremely densely populated.

We have some basic equipment at the moment that is allowing us to pump waste from the toilet/pits. However, due to the nature of the roads/hills -we then load the waste into 50L buckets (half full so they are lighter) that are carried up to a waiting truck on the road side. This can be over 100 barrels, 2.5 tonnes, meaning 100 round trips up steep hills with a bucket of sludge on your shoulder.

Is there another way?

The distance to the truck is 500-1000m; obviously sometimes the nearest road is downslope; but it is often 200-300m (vertical) distance up-slope.

Bear in mind that getting a large pump beside the pit is very difficult due to the narrow access paths and terrain.

All help appreciated. Is the reality that we'll have to stick to the carrying?

Nicola

 

[Nicolag]

Clean Team in Ghana are a start- up enterprise reverting back to a night soil type activity:

http://cleanteamtoilets.com/

Only problem for them is that they lose money as cleaning the barrel and disposing of the resultant waste water.

Nicola

 

[chicopee]

You could build trailers on wheels with several toilets installed on each trailer. I would label these trailers "toilet" trailers. Once a trailer is filled up, it can be pulled by several members of the village to the downhill waiting truck. The trailer can then be towed by the waiting truck which in turn has an empty "toilet" trailer to be pulled/ pushed by up the hill by the same villagers. Manpower should not be a problem and you partially solve the problem of unemployment.

 

[btrueblood]

If it's feasible to always go downhill, why not use temporary-ish piping and use gravity flow to fill the trucks.

 

[MartinLe]

I was about to mention compoosting toilets, but the OP stated they know a lot of low cost systems and more crucially want to use the waste for a bioenergy plant. But given that, as you mention, some pits are emptied every few years, are you sure you get much energy from them?

I want to pick up Bimr's idea with the tricycle and combine it with the vaccuum system seen in the first video:
Build the vaccuum system as seen here, but build it from a section of fat pipe. The hose for waste and the air pipe will attach to a flange on the top. on the botton, you mount a knife valve. Mount the pipe on your tank, close valve, operate vaccuum until pipe is full. shut off vaccuum, open valve, waste drops into tank, close valve, repeat. The valve should have the full diameter of the pipe & and could turn out to be the most expensive part.

This way your tank can be any old ICB or even a bag and does not need to withstand any negative pressure.

The bucket in the video is translucent, I'm not sure how you'd see the filling level in a piece of pipe. maybe keep the barrel and see if you can attach a flange to the bottom (if PVC, glueing should be possible) to mount a valve.

Possible problem is rags or anything clinging to the walls where the valve closes, blocking the valve.

Edit to add: Would it be feasible to have a duck bill valve or similar on the lower end of the pipe? So the vaccuum closes the valve, eleminating some steps.
I'd also think that the large seal surface achieves a better seal when small solids cling to the surface.

 

[gbangs]

Although not very likely 'low cost', but along the same idea as Ashtree's solar drier:
waste zapper article
I wonder what ever became of this?

gbangs
TC 8.3.3
NX 8.5.3.3 MP11

 

[Nicolag]

Sorry for delay but thanks for these helpful posts.

Martin - you are coming closest to whats feasible here I think.

(and you raise the important question, is this old sludge even useful - we are taking samples and testing for calorific value periodically to try build up some data around this - we only have 15 pits so far so not the greatest data set; but thanks for bringing this back to top of my agenda).

Finally got a video of our process uploaded:

https://www.youtube.com/watch?v=5S_8mLChMe4

We really need to drop the vehicle idea - no way to get any form of transport within 50m of all of these latrines (wheelbarrows included); and most often ~200m (though I do hope we'll work in easier areas where this is not the case).

What we really need to eliminate in the short run, is any visible sludge (to get us through an enviro health inspection) so the pouring is a no-no. Martin, I was thinking about what you were saying about the pipe or modification of the existing vacuum barrels to build a neater discharge system (not to a tanker as you suggest, but to the barrels that we carry to the road).

Possible to modify the existing barrels (though I'm reluctant to tamper with the one good thing we have). Only other thing I have found so far capable of withstanding such a pressure is some thick walled irrigation pipe that we could possibly try to mount a bottom end on and turn into a bit of a hopper system. Totally black so not ideal, but we'd find some way around knowing it was filling. We could try to use this upright and have a large valve to discharge direct to waiting barrels. Though I would fear for the valve (shitty locally made version) holding up through the repeated negative pressure build up.
[/u]

 

[MartinLe]

My thoughts are this: The shit will have to be carried between 50 and 200m, and every transfer of containers means you spread some around.

So why not use more of the white vaccuum barrels so that one is filled while the others are carried to the vehicle? Two people (4 with poles) can carry one vaccuum barrel. At the vehicle, you have hoist to ease lifting and tipping the barels into your tank. Something like a garbage truck uses to pick up waste. Still thinking how this can be enclosed, so you don't have a huge health hazard.

The barrels get lids for the trip. Possibly use smaller (=shorter) barrels.

I think it's unavoidable that some surface has shit on it after every trip and needs cleaning.
You can have vaccuum system similar to the one at the pit to empty the vaccuum barrels, then you move the dirt problem from the outside of the vaccuum barrels to the outside of the suction pipe/hose. This can be built with more enclosing (I actually have a rough idea how this would look like but no time to draw it now)

 

[Nicolag]

Thanks Martin

Of course! I never thought of that - if we manage to bring in roadside tipping we could just work with 10 or so barrels coming back and forth - so if I can make a less clunky/hard to lift vacuum proof barrel then we eliminate a round of pouring (provided its not too heavy).

Ok - i have to have a think about this. I was thinking of an intermediate hopper type system but was not really enjoying the concept - this is much better.

Unfortunately getting anything made that is a total nightmare - but we would happily ship them in if there was anything we could find that withstood the vacuum but was relatively lightweight.

Nicola

 

[Nicolag]

Estimated pressure build up of 0.7-0.9 bar for the current ~50L barrels. So if we brought it down to 30 would only need to withstand ~0.5. No experience with these materials so I'm not sure what we could work with.

All i've managed to find here is some thick walled irrigation pipe (310mm with 20mm walls)- similar to original barrel diameter.

 

[LittleInch]

I was thinking something like the attached.

This would be a single vacuum container, but then you insert into it the plastic sealable container - you can see many examples where you have snap type lids used for paint, fertilizer, etc. Trick is to make it small enough to be able to lift it out of the vacuum container so really no more than 20 - 30 litres, then stack them on a trolley and wheel them to the truck.

Lifting the top with the pipe out does mean some dripping but much reduced.

You do need some sort of liquid trap on the vacuum line to stop the liquid going into the vacuum pump, but I kind of assume you have something like this already?

The advantage is you don't need vacuum capacity for the transportation buckets.

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[Nicolag]

OK - I never even considered this as a possibility. You are saying I can have one strong tank which can withstand the vacuum and just insert my barrel for use inside? That would be fantastic if I could think of a way to get them out easily (perhaps via screw on lids with handles on?). Just lifting the lid would be a vast improvement over pouring.

I'll try and see if I can find something around the paint tub filling to get a better idea.

Yes - have a liquid trap.

Nicola

 

[KENAT]

Could your vacuum tank system be set up so the vacuum is only supplied to some kind of 'header tank' which you then empty into the non pressurized containers for transport to the vehicle?

Essentially take Little inches sketch but instead of the captive inner bucket have a suitable valve + outlet at the bottom?

Putting it up on a little portable tripod or similar may be enough of a head to get it to then poor down into your containers.

Work flow would be set up tank on tripod (or hang from tree or...), run vacuum pump to fill it, stop vacuum pump, open valve to poor the waste into transport container.

As to your containers what do use, literally buckets?

Might I suggest a more ergonomic container combined with a backpack type set up - backpack sprayers have this you just need to lose the pump & sprayer etc.

Or you might be able to just come up with a back pack harness for a '5 gallon' container or similar that may be more readily available.

Finally, is the terrain always so terrible you cant use some kind of cart to transport the containers? I'm not talking your typical red rider wagon but something like a game tote or deer hauler with two or even one large (almost mountain bike or dirt bike size) wheel.

http://gametote.com/index.html

Might take 2 people but seems if you can avoid carrying the drums - even only at say 50% of sites - that would be a big plus.

Or, if you can get your header tank high enough relative to your vehicle could you use a hose part way?

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[LittleInch]

Basically yes.

If you search "Quick opening closures" you should be good - the advantages here is that the vacuum applied will help seal the lid - all you really need is some locating lugs and a bit of a weight - some bricks or a person would probably do it if the seal is good enough. The trick is to get the sealing surfaces flat and the lid pretty strong.

Or a simple G clamp - there's bound to be a few of those hanging around

Something like this attached.

And a bin like this

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[KENAT]

In case it helps, schematic of my suggestion.

Header tank Schematic

It's approximately to scale assuming 6 ft poles for the tripod, location and types of valves I've indicated may not be ideal but I'm not a pump or sewage guy (yeah I know I may be full of it but that don't make me an expert in handling it).

Rough work flow after setting up.
[ul]
[li]Close container fill valve.[/li]
[li]Open waste extraction valve.[/li]
[li]Run vacuum until header tank is full.[/li]
[li]Close waste extraction valve.[/li]
[li]Turn off vacuum (may not be essential)[/li]
[li]Open container fill valve & fill container.[/li]
[/ul]

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[LittleInch]

KENAT - Pretty good - I would put the fill line at the bottom of the bucket but otherwise OK, Just add a vacuum release valve to allow the SH1T to flow out and that could work a treat.

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[KENAT]

LittleInch - sadly if I put the poop pipe down to the bottom of the poop barrel it obscured the poop text.:-(

Good point on the vacuum release valve, simplistically perhaps add manual override to the vacuum relief valve.

Or put separate release valve in equivalent location in the system i.e top of tank equivalent - could be anywhere on the line from the tank to the vacuum pump for instance - maybe the vacuum pump controls already have one in?

So work flow becomes:

[ul]
[li]Close container fill valve.[/li]
[li]Open waste extraction valve.[/li]
[li]Run vacuum until header tank is full.[/li]
[li]Close waste extraction valve.[/li]
[li]Turn off vacuum (may not be essential)[/li]
[li]Open vacuum release valve (not shown in schematic)[/li]
[li]Open container fill valve & fill container.[/li]
[/ul]

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[KENAT]

Refined per LittlInch.
[ol 1]
[li]Ensure container fill control valve closed.[/li]
[li]Ensure vacuum release valve closed.[/li]
[li]Ensure waste extraction control valve open.[/li]
[li]Run vacuum until header tank is full/pit emptied whichever comes first.[/li]
[li]Close waste extraction control valve.[/li]
[li]Turn off suction pump (may not be essential depending on power source etc.)[/li]
[li]Open vacuum release valve.[/li]
[li]Open container fill valve[/li]
[li]Fill container to desired level.[/li]
[li]Close container fill valve.[/li]
[/ol]
Repeat steps 8-10 until header tank is empty.
Repeat steps 1-10 until pit is empty

Detail design may be able to come up with more elegant valve and piping arrangement or even introduce interlocks or similar to force correct process but I'm an ideas guy not details. ;-)

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[Nicolag]

Damn I wrote a response but it got lost in the Rwandan internet.

Header tank
i have considered this and i have had the tank itself made (just 50L since the workmanship is poor, so I don't want too much negative pressure in there).My issues was
(a) how to safety control air valve on top of header tank (this could be 1.8-2m high by my calcs)
(b) what kind of valve to put connecting to the transport barrel. We have to have a 3" opening here so that it doesn't block. I was looking at ball valves as the most likely readily available option to withstand the vacuum but they are so clunky and difficult to use, certainly not something that you can easily just open and close for discharge. is there something better I can do here for fast discharge?

Little Inch, I fear I may be an idiot.

I'm not getting how the lid works in that system. My understanding is attached, but I feel like you're telling me it can happen inside...I totally don't understand how I can fill the barrel yet get a lid on it. Am I going mad?!

 

[KENAT]

Valves don't have to be on top of tank - anywhere in that pipe/hose between pump and header should work. 'Id think where the pipe connects to the pump may be Good idea for ease of use.

What level of vacuum are you running?

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[LittleInch]

No, you seem to have got the idea.

The only change from what I think you have now is that instead of filling the vacuum pot and pouring it out, you fill a container which you them lift out of the vacuum pot after putting a lid on it.

It's better if the filling tube goes to the bottom of the inner container to avoid splashing and the suction tube has a float which stops the "liquid" from flowing into the vacuum pump and also tells you when the container is full.

3inch full bore ball valves are normally very simple and easy to use with a quarter turn bar type operator

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