Hi Dale,
Thank you for your great feedback on our recent paper 'Designing local solutions for emptying pit latrines in low-income urban settlements (Malawi).' Trash is a big problem to fully empty latrines here in Mzuzu, Malawi. Households use pit latrines as a garbage can, even at my house.

About the keyhole (squat hole), please see our other recent paper 'Characterization of pit latrines to support design and selection of emptying tools in peri-urban Mzuzu, Malawi.' In this work you are correct that we suggest a maximum pit latrine emptying tool diameter of 10 cm to fit through the keyhole (squat hole). In Malawi, we do not have standardized latrine designs, and the only pit access is through the keyhole (squat hole) or to break the floor.

Hope this is helpful and please feel free to contact me if there is anything else.

Rochelle

Rochelle et. al.

I carefully read the paper Designing local solutions....... regarding pit emptying in Malawi. I have a few follow up questions.

In the pits that the device could not successfully empty, what were the problems?

If the problems were trash getting stuck in the valves inside the gulper, I've often wondered if anyone has tried flexible check valves (sometimes called duckbill valves because they look sort of like a duck's bill) in such devices. I would think these would be a lot more clog resistant than other types of valves. Can you address this question?

You give a typical flow of 0.00058 cubic meters per second (0.58 liters per second) and give times to empty typical pits as 10-15 minutes for the sludge pumping part of the process, with additional time for set up, clean up, etc. This gives a pit volume of around 0.5 cubic meters or less. This seems much smaller than typical pit sizes that you mentioned earlier in the article. Were the pits only partially emptied?

You give some typical dimensions of the squatting hole in Table 1. One hole is listed as "round", but are the holes typically, rectangular, elliptic, keyhole shape, etc? I ask because I'm interested in tools that can go down through the squatting hole, and it seems the larger the hole, the easier the process. Someone recently said "Assume 10 cm diameter" for a squatting hole, but is this excessively restrictive? I notice all the holes in Table 1 are much larger.

Thanks,

Dale Andreatta

Note by moderator: This thread is related to this research project:
forum.susana.org/component/kunena/99-fae...ty-and-policy-issues
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Please checkout our newest publication under the "Solutions for Pit Desludging and Subsequent Sludge Management in Low Income Urban Settlement in Malawi” project with support from the Water Research Commission of South Africa.

Designing local solutions for emptying pit latrines in low-income urban settlements (Malawi)
by W.C. Chipeta, R.H. Holm, J.F. Kamanula, W.E. Mtonga and F.L. de los Reyes III
Physics and Chemistry of the Earth, Parts A/B/C
dx.doi.org/10.1016/j.pce.2017.02.012

Abstract
A lack of effective options in local technology poses challenges when onsite household sanitation facilities are eventually filled to capacity in unplanned settlement areas within Mzuzu City, located in northern Malawi. Vacuum trucks currently dominate the market but focus on emptying septic tanks in the more easily accessible planned settlement areas, rather than servicing the pit latrines common in unplanned settlement areas. As a result, households in the unplanned settlement areas within Mzuzu rely primarily on manual pit emptying (i.e., shoveling by hand) or digging a new pit latrine. These practices have associated health risks and are limited by space constraints. This research focused on filling the technological gap through the design, development, and testing of a pedal powered modified Gulper pump using locally available materials and fabrication. A modified pedal powered Gulper technology was developed and demonstrated to be capable of lifting fecal sludge from a depth of 1.5 m with a mean flow rate of 0.00058 m3/s. If the trash content was low, a typical pit latrine with a volume of 1–4 m3 could be emptied within 1–2 h. Based on the findings in our research Phase IV, the pedal powered Gulper modification is promising as a potential emptying technology for lined pit latrines in unplanned settlement areas. The success rate of the technology is about 17% (5 out 30 sampled lined pit latrines were successful) and reflects the difficulty in finding a single technology that can work well in all types of pit latrines with varying contents. We note that cost should not be the only design criteria and acknowledge the challenge of handling trash in pit latrines.

To help you access the full article, it is open access, please visit www.sciencedirect.com/science/article/pii/S1474706516300523 .

Greetings to All,

We have wrapped up four phases of design and testing for the modified Gulper here in Mzuzu, Malawi. Major findings included that it was difficult to make it low cost as our targets, and still be able to pump sludge with a high volume of trash. I am currently wrapping up the MSc in Sanitation Degree at Mzuzu University.

The intellectual property developed under the project and any possible revenue distribution is covered under the Water Research Commission policy of our project.

We are working on a publication outlining our design and testing approach. We will post is on the forum when it is available. If you are interested in continuing work on the low cost pit latrine emptying technology, please drop us a note offline.

Warm regards,

Willy Chipeta.

Hi Andrew,

Thanks for asking a about the technology development. And again sorry for the short reply last time. Just got caught up with things that i failed to come back to you with an appropriate response.

Modification of the pedal powered treadle pump failed. Therefore moved on to explore the modification of a pedal powered gulper pump.

The modified pedal powered gulper design comprises of a pedal propelled mechanism using a motorbike chain and crank connected to a flywheel (diameter 600mm). When pedaled motions are imitated the flywheel enables up and down strokes of a connecter handle that attaches to handles at the top of the gulper inside the pit latrine. This phase was fabricated at Mainga Engineering work shop at a cost of USD$406 within Mzuzu City.

A summary of testing results for the pedal powered Gulper design and other research work is attached for your review.

Hi Willy, how is the pump development going?

Hi Andrew,

The sizes of the valves were 10mm.

warm regards,

Hi Willy,

How is the pump development going? I've been working on the design of a manual pump myself. I had a prototype of it at the toilet fair in India last year. There are some videos on the site that you can search for if you want to see what it looks like. I'm just finishing up a new design of the pump and over the next few months will be refining it. I'll post some pictures when it is ready.

Early on in the development of the pump I explored making it pedal powered. I liked the idea of riding up to a pit, engaging the pump mechanism and pedaling the bike to power the pump. I also looked at a pedal powered pump that was not integrated with a bike. It proved to be too complex and the mechanism wasn't ideally suited for pedal power. I may revisit the mechanism at some point but for the moment I'm going with arm power.

I watched your video and have some thoughts. Without actually working with your pump or at least seeing your detail drawings it's a little hard to evaluate but maybe this input will be useful.

1. The longer your stroke length is, the more efficient your pump will be (to a limit). The reason for this is every time you change direction, your one-way valves (check valves) need to open or close. Every time the are opening or closing, they are reducing your efficiency as material slips past them or they don't serve their purpose. If your cylinder were very short, the valves wouldn't have time to actuate. So the longer the better...

2. Except that you don't want a stroke length that exceeds the range of motion of the human providing power. More specifically, you don't want the stroke length to exceed that which the human can transmit through the mechanism when the human is keeping their stroke to the most efficient range. With arm power, at least on my pump, I consider that range to be about 20 inches. With leg power it might be 8-16 inches depending on the mechanism.

3. Since you are using pedal power, it's easy to argue that the ideal stroke is what a conventional bicycle has, after all, the geometry has had 100+ years to evolve and it hasn't changed much since early on. The next thing to define is the mechanism that converts your rotary petaling motion to the reciprocating motion of the cylinder.

4. Something to keep in mind while designing your system: the diameter of your piston (the bore) is important. The bore and the stroke are going to have a big impact on how much power your system needs and the design of your mechanism. You don't want the bore to be too large as the human powering the system may struggle or you'll need to gear the system. I suggest keeping the system as simple as possible so you'll need to carefully select your bore and stroke. My arm powered system has a bore of 70mm or so.

5. Another consideration is the design of the piston and the seals. Poor seal design will result in fluid or air getting past and a decrease in efficiency. Or, the seals will produce too much friction and require more power - the operator is going to get tired quickly.

6. You also need to prevent the piston from pivoting in the cylinder. If it pivots, it seizes. The design of the piston plays a part in this and so does the length of the piston rod. Ideally, the end of the piston rod will only experience vertical motion but that isn't necessarily practical. This is one of the very nice things about a two piston treadle pump; the piston stroke can be purely vertical. Anyway, you'll want to design your mechanism to reduce how much the piston rod and piston pivot. One way to achieve this is to maximize the distance between your rocker pivot point and the point where your piston rod attaches to the rocker. The "rockers" on your 2nd prototype are the 2 bars connected to the sprocket above the pump cylinders.

7. You should also try and get the point where the piston rod attaches to the rocker to be directly above the cylinder. You don't want it being off center throughout it's entire motion.

7. You mentioned that you are using a motorcycle chain instead of a bicycle chain because the bike chain was breaking. If the system is designed well, and the chain is properly aligned, a bike chain should be sufficient. I suspect you didn't have the chain rings / sprockets lined up. Or maybe it was a chain quality issue. Looking at one of the pictures, it seems that your piston rods are attached to the chain. Is that right? If so, I'm not surprised the bike chain broke, they really don't take side loads well. The approach you took in prototype 2 seems more sound.

8. What type of valves are you using?

9. Lastly, you are right. 2" diameter hose presents problems. We tested various sizes over the course of the Omni-Ingestor project and 3" seems like the right compromise.

Good luck with your work.

Cheers,

Andrew

Dear Willy,

You have probably in the meantime already connected with Nicola by e-mail. But in case not (and in case other people also don't know): Any forum member can contact any other forum member by using the "message" button which you see to the left of the person's post (you need to be logged in to be able to send your message).
Therefore, there is no real need to ask for someone's e-mail address.

If you want to make it even easier for people to contact you, you can also add your own e-mail address in your forum signature. An explanation on how to do that is provided here:
forum.susana.org/forum/categories/134-us...-with-video-tutorial

Kind regards,
Elisabeth

Hi Nicola,

Thankful for your informative reply.

The gulper version we tested was the first one and not the rammer,

I found the task to be heavy when riser pipe is full with faecal sludge,

My thinking was that since arm muscles tire easily and are less powerful than leg muscles then we can potentially easy the emptying process including denser sludge in the bottom layers.

Please can you let me know on the dates for your testing and a letter of invitation can help in me requesting for permission to visit if possible.

I will try to attach a video of the idea that I had fabricated as part of my studies at Mzuzu University for your review.

Please send me your email so that I can send it to you and give me your honest thoughts about it.

Warm regards,

Hi Willy

What exactly are the flaws with the current Gulper that you are trying to improve on?

I never really understood the benefit of a treadle mechanism...of all the problems with Gulping, getting tired arms is not the worst!

The main issue we now have, is we have converted a version of the Gulper (the Rammer - which rams in, rather than relying on suction) to 3m (which perhaps overcomes the issue you mention). Then we have an issue because stroke length limits how deep you can go. Thats when you start need an alternative pumping mechanism - perhaps thats what your were thinking about anyway.

The photos attached are not our most recent version (with the extension) but i'll have some of that early next week.

Testing in Blantyre if you ever want to visit.

Greetings to All,

This is to share progress on research progress. I have been exploring treadle pump modification but using suction power did not ably lift weak mud slurry hence was abandoned.

Recent efforts are on possible gulper modification using peddling mechanism than use hand operation. Any ideas on how to make this transition possible are welcome.

Warm regards,

Willy Chipeta

Masters Student in Sanitation at Mzuzu University, Malawi