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

 

[ashtree]

Nicolag

No matter what you use you are going to have up to 1000m of hose if that is how far away the truck is and the 2-300m vertical is going to be a problem.

The reality is i would expect, that if you want the liquid in that truck you are going to have to carry it.

So perhaps there has to be an alternative solution thought through.


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[Nicolag]

great - thanks for the feedback.

That's essentially what I'm trying to establish: will I ever be able to do this via a pump/series of pumps or do I need to get real and just keep planning around the container carrying system.

 

[MikeHalloran]

Some camping trailer parks here, instead of providing a distributed underground sewage system, bring you a 30...200l tank on wheels, into which you discharge your accumulated waste water. Then the portable tank is pulled to a truck or a central drain. It's a nice system for level paved roads. For goat paths, not so much.

The thought occurs that maybe the buckets you're using are perhaps not optimal. Find a history of honey buckets and you might find a better shape than whatever you're using. Or do some experiments.

You can't pump honey that far up a hill with the pump at the top. Carrying the pump down to each latrine is impractical. Using a jet pump at the top increases the volume of what you have to deal with. Have you got the budget and the power source to put a pump at each latrine, and provide permanent piping up to the truck, or a holding tank?

Can you persuade the citizens to climb a hill to use a toilet, as in a nicely equipped modern latrine up high, accessible to the truck, or mounted on a trailer and towed away to discharge?



Mike Halloran
Pembroke Pines, FL, USA

 

[Strong]

What about a transfer tank either on a skid or aerial tram with the a winch powered by the transfer truck? You would then "only" need a reasonably straight path to raise or lower the transfer tank between latrine and truck. You should avoid liquid containers that are partially filled, since they are unstable from the sloshing free surface. Either completely fill a smaller container or perhaps consider an air bladder or something else to stabilize a partially filled container. Where there is a will, there is a way!

Walt

 

[bimr]

Use a small tank mounted on the chassis of a motorised tricycle. It is not practical to haul wastewater 500 meters.

http://www.unesco-ihe.org/sites/default/files/fsm_ch04.pdf

 

[georgeverghese]

How about a hand operated or air operated Wilden pump (on a truck) to transfer this sewage ( from a discharge port at the bottom of these receptacles)?

 

[LittleInch]

Hmmm. lets look at some basics here. 200 - 300 m vertical implies a pressure at the base of any pump or line to be approx. 30 bar. That's quite a lot and would need some reasonable wall thickness hose, even if was only 3 or 4" and then would still be full of "liquid" when you're finished, so might end up being as heavy as the current system.

You might be better off thinking along the lines of a small vacuum / pressure tank and a small air / vacuum pump and say 200m of hose. Then for the ones furthest away or steeper, pump into the same tank in a cascade system. This would reduce the pressure in your vessel to around say 10 barg.

You vacuum out the waste, then turn the pump around and pressure up the tank to blow the waste down your pipe either to the truck or to the next tank in line. You should be able to make it small enough to attach some wheels and be able to push / pull / carry the tank and hose.

This is a similar set up to what they do when spreading slurry on a farm, they vacuum up the slurry, then pressure the tanker to spray it out the back.

Something like this

http://www.sswm.info/content/human-powered-emptying-and-transport

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ashtree]

Gents,

Get on Google Earth and have a look at Kigali. Its going to be tough to do anything given the "specification".

My opinion is that pumping is not the answer, too far , too much lift, too much equipment to haul too many variables , and difficult terrain.

Therefore i would suggest that bimr is on the right track. Mechanize the hauling of the buckets in effect.

Maybe a tank and some small pumping equipment could be mounted on a small all terrain vehicle, so that it is relatively self contained and delivers its load of say 50 gallons back to a tanker.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[Artisi]

Pumping is not a consideration even in your wildest dreams.
It will need to be manhandled as it was in my youth in Australia, the dunny-man called once a week to remove a full pan leaving an empty one in its place, worked well as there was no other alternative.
Google dunny-man Australia.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[georgeverghese]

Another option may be a hand or air operated Moyno pump - for 200m vertical rise, break it up into a few intermediate pumping stages and holding tanks to suit.

 

[Nicolag]

Thank you - the above is really useful. Some are some thoughts I've had (I'm pretty familiar with all the low cost systems currently out there - these hills have just added a new dimension), some are new thoughts.

What Artisi has said about the data is really critical. I present you the worst case scenario; but we are really not sure if that represents 5% of the 'market' or 50. To understand this would be a fairly serious undertaking. The baseline everywhere is of course very dense but the distance/head to drive-able road is massively variable area to area.

I imagine we will need a range of systems and a pre job assessment will have to identify which system to use each time.

If we forget the transport for a second (re-inventing how to carry stuff up hills is difficult!), let me tell you about our current system closer to the pit. We use a Vane pump to build up a negative pressure in thick walled barrels, close the valve, and sludge is sucked in. We then pour to the 50l barrels (half full) so they can be carried. The thing we really need to avoid, is human exposure to sludge, so the pouring is not idea.

I haven't got good enough internet to upload a video of our process, but you can see an example of the machine here:

https://www.youtube.com/watch?v=igy81IvqvR8

The most important thing to watch is the pouring of the waste. We don't pour into a nearby pit like these guys as the area we work is too dense - we pour into 50L barrels to carry to a road side.

Any idea how we can go direct to those smaller barrels (Even if we do need to make them smaller as suggested in a post above) to avoid the pouring?

Its also worth noting that the real 'exposure' part is at the start. These pits are full of solid waste, and we begin by fishing out rags with a hook. No matter what system we come up with, we're not doing well to overcome this.

https://www.youtube.com/watch?v=6gbDNf1uybo

 

[Strong]

Is this how the saying goes? To an optimist the barrel is half full; to a pessimist the barrel is half empty; to an engineer the barrel is the wrong size!

Walt

 

[1gibson]

Nope, just has a safety factor of 2.

 

[georgeverghese]

These rags would get in the way of just about any pump you can throw at this service. Educating these people would be one amongst many longer term tasks. In the meantime, a blowcase would avoid the use of a pump, but you need high press compressed air for this..

 

[ashtree]

Gents

The rags i saw in the You tube were not really that much worse than what you get on the inlet screens of a municipal waste water plant in terms of size and nature. However in such a circumstance there is normally a lot more dilution ie: less rags and more water.

But the problem is not lifting out of the pit but getting it away somewhere to do something with the waste.

Nicolag

In general terms how often are pits pumped out? Weekly, monthly , yearly

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[Artisi]

The whole concept needs rethinking, commencing at the home level. Think about filling in all the pits and trenched and revert to a single pan system for each house, emptied weekly or as necessary. The weekly dunny-man calling in the early hours of the morning worked well in many areas of Australia - admittedly not an ideal method of disposing of human waste but probably streets ahead and manageable compared to the present system


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[ashtree]

Artisi

I think you are right. Remember Brisbane had "night soil" well into the 70s and would be a real and workable solution. Only trouble might be how far the dirt collector might have to walk to get back to a truck. Most cities that were laid out with night soil in mind had lanes at the rear of the property.
Nonetheless i think it could at least be a partial solution.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[ashtree]

I have been trying to think through some totally alternative methods as well. I am sure that these would be problematic in some way but i am still going to float out these ideas for discussion, just to get the ideas flowing.

1) A portable latrine system with the outhouse built over a tanker trailer or as part of the tanker itself . When the tank is full you tow the trailer away. Obviously this wont work everywhere because vehicle access is a problem already, but may also offer a partial solution.

2) A system that uses a solar drier to dry the solids out after a short digestion period. This would require a site with some slope so that the sludge can flow under gravity to the solar drier which would be roughly something like a glass house only made out of a plastic clear film. The sludge would be substantially drier , therefore less volume to carry but would have to be dug out of the drier and carried in wheelbarrows. Still a better option than carrying a bucket. Likewise the heat of drying and the solar radiation would reduce the bacteria levels in the sludge. Lots of problems and some complexity and probably wont be suitable for a lot of sites



Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[Nicolag]

The wrong size barrels are pretty handy to be honest as it allows us to be a bit more sloppy with the pouring. Only other hope is to suck into some intermediate tank what releases precisely the barrel volume. Any barrels less than 50L do not come as standard here, unless you look at using the standard water jerry can.

Again of course I agree, its a complete re-invention of the system that is necessary. Particularly for us, because we have a waste-to-energy plant and the newer sludge has far greater value than the older stuff. That said, by the time you get to a latrine (in their current form), you might as well empty as much as you can when you get there because it's already been so much hassle to set up (and customers get pretty upset if sludge is still within sight). I would love to, as part of our current work, block off the depths of the pit and build it so that it can be emptier (a) more easily, and (b) more regularly as part of our current work; but that would be a huge social change for people who value a pit latrine as deep as physically possible to avoid emptying completely. Maybe I should revisit this thought.

Pits can be up to 7/8 m deep - more typically 3m (people often tell us they are 10m but i think this is just because the builders charge them by metre, so they mis-quote them on how many metres they have really dug). We're finding that people empty ever 8-15 years (very variable numbers of users). Some of the settlements in town are so new that they have never needed to be emptied.

In the restaurants, pubs - we get nice sludge - not so much trash. But the households ....lets jsut say the pit yesterday had a mosquito net and a football + 200L of shit covered trash.....

Bear in mind this is the situation across ~ 50% of the population of most African cities - so its worth thinking about...but a bulldozer often comes to the fore as the better option ;-)