As usual, I'm a week behind in my Susana reading.

Jamie Radford posted something above that he was going to try to clog my Sludge Digger. If the sludge is VERY thick it won't drop out of the bucket when the bucket is dumped. That's probably the only way to clog a Sludge Digger.

Jamie, I looked carefully at the photographs of sludge of various strengths that you posted a couple weeks ago. As best I can tell, my Sludge Digger will work up to a sludge strength of 2000 Pa. Is there a simple way to test this? I suspect that I might be low in my estimate of 2000 Pa, and if so I'd like to know this. I could probably build a cone penetrometer, but this would take some work. Are there any videos of sludge of various strengths? Can one do some sort of slump test? Is there a relationship between sludge strength and angle of repose?

As an update, I'm working on a version of the Sludge Digger that is all-metal for increased durability (except possibly for the handle and rope). Also, some of the clearances are tightened up for a more solid feel. My colleagues who are metalurgical engineers say that in high Ph lime stabilized sludge ordinary steel (not stainless) should work well. Time and testing will tell.

Dale

Dale,

Thanks for posting - I'd forgotten about your sludge digger and good to see it's evolved from the earlier prototype I'd seen a year or two ago. I'm also going to follow-up with you offline to get a feel for what testing you've already done, and see if we can get it benchmarked under the same process as the other pumps we've done/are doing. I'm also now itching to try and make it clog - I like a good challenge! Although I agree it's clearly far less likely to than manual pumps with sludge flowing through valves.

I'll be in touch. All the best, Jamie

Dear Dale,

I looked at the video of the Sludge Digger, and I think it would work well with our program. I have always thought that there must be some simple bucket system that could alleviate the problem of septage workers entering tanks to desludge them. The Sludge Digger looks like it fits that exact need. Treating the waste in the pit with the lime stabilization process takes out the "yuk" factor, which is the first step in trying to elevate the stature of septage workers from "under class" to people providing a safe and valuable service. The lime also makes it really easy to handle the wet waste once it is removed from the pits, and to properly disperse the biosolids once they are air dried for a few weeks. And of course, since the waste is treated on-site, there is no need for an expensive treatment plant.

I want to take you up on your offer of helping us to procure some Sludge Diggers for our project in Myanmar. I will discuss this with you off line. For now, let me leave you with a video that further describes the In-Pit Lime Stabilization process. This video is by iDE Cambodia who first demonstrated how this age old technology could be applied to difficult to empty pits back in 2013.



Kind regards,

Dave

Thanks so much for this information. Please follow our progress at:

forum.susana.org/forum/categories/53-fae...--and-the-answer-is-

The strategy is developed in part through your inputs. Thanks again.

Dave

Mr. Robbins,

Also please consider using my Sludge Digger design, seen at:



This video was a prototype but you can see its main features. A more final version is seen in the attached still photo, and the manual for building them is also attached. The final version is much sleeker and simpler than the one in the video.

The Sludge Digger is basically a bucket pivoting on a stick, with a rope. It handles thin and thick sludge, and will never clog. As seen in the video, the Sludge Digger easily picks up bottles, diapers, and various other forms of trash.

Under ideal conditions (shallow pit, thin sludge) it will pick up sludge at a rate of 2.2 cubic meters per hour. Most of the time it would be slower, of course, but you could also have two men working in parallel with two sludge diggers, one man dumping his bucket while the other lifts from the pit.

Comparing with the pictures in Jamie Radford's very helpful Visual Guide to Sludge Strength, I would say the sludge digger can handle sludge up to at least 2000 Pa, probably thicker.

It appears that you have a small scale project with three men allocated for clearing pits. Depending on the distance from the pit to your transport vehicle, you could have two men carrying buckets while one man clears the pit, or two men using two sludge diggers and one man carrying buckets if the pit were close to the transport vessel.

I don't know what the price of the sludge digger would be, but it would be virtually nothing compared to all the other technologies being considered. This frees up extra money in your project. If you would like to make some sludge diggers, you may use the attached manual. If you would like me to build one or two sludge diggers and ship them to you, I am willing to do so, at my expense.

Dale Andreatta, Ph.D., P.E.
This email address is being protected from spambots. You need JavaScript enabled to view it.

Thanks Jamie for this great information. As for the sludge characteristics in our project, I think we will likely see the entire spectrum, but the majority will be in the greater than 2,250 Pa category, making it very difficult to pump.

There is another option we are considering, based on a study I learned about from IDE at the FSM3 conference in Hanoi, where the FS is stabilized by hydrated lime within the pit prior to pumping. For this, the waste would have to first be diluted to say, 200 Pa by mixing in a slurry of hydrated lime and water. This should then pump readily once the stabilization process is completed. The lime stabilization process should also greatly reduce the odors and make the waste much easier, and less objectionable to manage. The key here will be the mixing.

Thanks again for your feedback. I will post updates as they are available.

Best,

Dave

Hi David,

We've been testing the performance of various FS pumps to try and answer exactly that question. The original intent was to undertake a comprehensive benchmarking exercise of manual and mechanised pumps - including the Excrevator, eVac, ROM and various 'standards' for comparison - eg Vacutug, hard working poorly-maintained vacuum tanker. Sadly due to limited funding at the moment we're just testing manual/semi-mechanised pumps (Oxfam diaphragm, Gulper I, Gulper II [aka Rammer] and the Omni-Ingestor manual pump - once redesigned). We are though working with Water for People who have tested both the eVac and a cheap centrifugal pump (their 'PumpandGo' concept) in Uganda. The intention is to follow-up with an expanded phase 2 that provides some more definitive answers once the value of the exercise has been demonstrated.

So, to your question: Which pump is most appropriate for very dense sludge at the bottom of pits that may contain trash?

Taking the first part we probably need to better define 'very dense' - a relative term that no doubt differs wildly between Manila and Durban according to the types of faecal sludge found in each. To get around this we've been measuring undrained shear strength, which is a good indicator of 'pumpability' - at least without any trash in the mix, and put together the attached visual guide on strengths. Above ~2kPa the sludge is semi-solid and with limited flow (you can see in the picture it is holding it's own shape), so (unless you are fluidising by adding air/water) you will need to move the pump inlet around the pit to empty it. Below ~1kPa the contents are 'wet' and pumping from a single point works.

Testing pumps on 'pure' FS (simulant) without any debris, produced the following flow rates:

Strength range	Ave. strength (Pa)	Flow rate - G1 (l/hr)	Flow rate - G2 (l/hr)
1	60	2170	870
2	150	1730	780
3	230	1070	550
4	360	500	380
5	510	0	210
6	630	0	0

Comparing that to your 0.8m3 = 800 l/hr suggests that you're down at a sludge strength of a few hundred Pa - which I expect is probably weaker than what your'e dealing with.

[A couple of caveats:
1) These flow rates are averages over a 1min period by researchers, not pit emptiers. Expect the average over an hour to be lower - even allowing for the physique of regular manual pump operators.
2) This data is for the original T-bar handle at the end of the shaft for both G1 and G2, the new design with a donkey-tail lever arm for pumping is more efficient and will achieve higher flow rates - particularly for the G2 and at higher strengths where flow rate is limited by power not stroke speed.]

Adding solid waste into the mix is inevitably going to reduce the average flow rate due to time spent clearing blockages - in Kampala they often spent an hour 'fishing' trash from pits before attempting to empty, and when blockages do occur they take 20-30mins to clear.

We're currently extending our testing on these manual pumps to include trash, and updating our business model to account for differences in time taken to clear blockages etc. so I don't have any real data on this yet. That said, your average flow rate looks ambitious if using a manual pump, and certainly if there could be trash in the pit.

Anecdotal feedback from testing the eVac was that it was a little awkward operationally as it was difficult to tell when the vacuum chamber was filling - and it's relatively small size made for regular opening and emptying. George Drummond might be able to provide more detailed feedback. We're hoping to benchmark the eVac's performance with WfP in the not-too-distant future.

Tate Rogers is probably best placed to comment on the Excrevator - I know they were looking at trash handling and experimenting with various different macerators to try and prevent long stringy material from binding around the augur. It should generally work better at higher strengths - subject to having to move it around the pit when the sludge ceases to flow. The only data I've got on strengths was the pit of simulant at RTTF India which they comfortably pumped - that was around 350Pa. I know they were testing sludge strength with a manual cone penetrometer during field trials - there may be some conclusions you can draw from that on flow rates/performance etc. (correlating the manual cone readings to shear strengths is another one on the 'To do' list)

Clearly there are very different unit costs to throw into the mix as well - the Gulper I and II are ~$100 and $200 respectively when locally manufactured in Uganda, cost of the eVac and Excrevator will probably be dominated by whether you need to include a motor/genny or if there is something at the IDP camps that could be used for those 2 days a week for emptying.

In conclusion:
1) It depends how strong is "very dense" - if it's over 1kPa I expect your options are Excrevator or a shovel
2) Not knowing how the excrevator performs with stringy debris, I would expect that they're all going to struggle - which will probably control emptying time far more so than the strength of the sludge, so the Gulper I is probably as good as we've got at the moment.

Do get in touch directly if you'd like to discuss further - and we'll post some updates on progress with our testing. The Omni-Ingestor manual pump has been designed to be much easier and quicker to clear blockages than either Gulper 1 or 2, so that may be a good option in perhaps 6months/a year's time.

All the best, Jamie

Hello,
For advice on testing FS tools in IDP camps in Myanmar, please checkout our work in Malawi at:

forum.susana.org/forum/categories/99-fae...ty-and-policy-issues

You might be interested in our results, but if our conditions are different than yours consider adopting a similar methodology to our testing as we have used the gulper, Excrevator, as well as locally developed technologies.

Rochelle

Dear friends,

Solidarites International (SI) is providing humanitarian and development assistance to Internally Displaced People (IDP) camps in Myanmar. As an indicator of their progress, over the last 4 years they have virtually eliminated diarrheal disease in Robert Camp, where it had once been rampant. This is achieved through hand washing, solid waste management, water supply, and an active latrine and septic tank construction and maintenance program. To transition from humanitarian aid to development assistance, SI is promoting onsite FSM where teams of local residents would hygienically collect and transport the fecal sludge to an onsite treatment system. Space is very limited so the lime stabilization method will be used (using lime to treat septage is already practiced in Myanmar). We will purchase the equipment and teach the local workers how to use it. We are assuming it will be either the Gulper, Excrevator, eVac, or possibly a non-clog centrifugal pump. At this point we just don’t know which one would be the best. Ideally, we would be able to trial each. There is a highly committed and technically able team, an actively engaged stakeholder group, and a supportive local government. This could be a very useful case study for demonstrating small flow, cost recoverable FSM programs.


The advice we are requesting is which of these technologies would be most appropriate for sludge that:

- Is very dense at the bottoms of the pits

- May still contain some trash, rags, plastic, syringes, although significant progress in “anti trash dumping” is already demonstrated

If you are interested in this or would like to provide input, I have attached the project brief which details the intervention.


Thanks most sincerely from the SI team for any thoughts you may have on this project.