Sludge pumps with better valves?

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  • dandreatta
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Re: Sludge pumps with better valves?

I think Kelldigest's question was actually for me.  As far as I know there hasn't been any progress with the pump since I left Nairobi.  After posting the video on youtube I haven't done any more work on it in the US.  I have mixed feelings about whether it is even useful or not, as the simple scoop that the pit emptiers are currently using is so simple and not a lot slower than the pump.  

Dale Andreatta
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  • awhitesell
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Re: Sludge pumps with better valves?

Hi Seamus,

If your question was in regards to my valve and not Dale's, I haven't made any progress on my valve. The design work is done but I need to come up with a few thousand to prototype it and several thousand more to make a new test rig and perform the testing. Finding funding has been very challenging unfortunately.

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Andrew
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  • Chaiwe
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Re: Sludge pumps with better valves?

Dear Dale and Andrew,

I had the privilege of co-organising a pit-emptying technology testing mission in Zambia in late 2017. The technologies trailed within pits in Lusaka's densely populated settlements included the Flexcravator ( provided by North Carolina State University, USA), the eVac (Provided by Partners in Development, South Africa) and the Gulper (Sanitation Solutions Group, Uganda). 

The trail used the Technology Applicability Framework (TAF)  method to assess how applicable the technologies were to the local context. The Gulper of all 3 technologies failed miserably for many reasons, including similar to what you mentioned in your discussion.

1. It was in many cases unable to fit in the toilet facilities for various reasons; Interface being too small to allow entry into containment, low roofing, narrow or low hanging doorway. etc
2. It couldn't handle solid waste at all, clogging frequently and lengthening emptying time. 
3. It required fluidising of sludge by adding water (a resource that is already soo scarce in many of these informal settlements).
4. It could barely handle thick/ dense sludge (a consistency that is common to pits in Lusaka).

I would assume that Malawi and Nairobi have similar characteristics to Lusaka and so would assume all of the above apply?  In the case of kampala, where the technology seems to be more popular, the sludge consistency seems to be more fluid with less solid waste(my own observation having seen it in action there). Conclusively, Lusaka opted to address its solid waste problem and work on facility standards to address challenges that come with pit-emptying. 

Take a look at a similar discussion on the technology testing in Lusaka here:  https://forum.susana.org/99-faecal-sludge-transport-including-emptying-of-pits-and-septic-tanks/22131-improved-pit-emptying-technology-flexcrevator

EXTRACT:

A major problem of pit emptying in Lusaka is the high content of solid waste in the pits which obstructs every mechanized emptying, no matter whether manual (Gulper) or motorized (eVac, Flexcravator). And the problem is not the real solid waste like brooms, bottles, tins, shoes, bones which are either easily rejected by a cage at the suction pipe inlet or by the auger of the FlexCravator, but the immense quantity of plastic bags (and rags and cloths).

These get into the pit either as wrapping of kitchen waste, baby diapers, MHM remains or as anal cleansing material. And every of the three pumps tested was heavily affected by all the plastic which sooner than later blocks any cage, auger or suction pipe. Then the pump has to be pulled out and cleaned of the plastic which inevitably leads to spillage of FS at the site.

It is not fair blaming the pumps failing to handle the plastic but it is an immediate effect of its presence and before we think about using any type of pump emptying latrine pits in Lusaka we have to solve the problem of solid waste/plastic going into the pits which is caused also by the failing solid waste management system. The current pit emptiers in Lusaka use long arm buckets and rakes to empty pits from FS and solid waste, which seems so far the most appropriate technology.

Regards,
Chaiwe
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(Under consultancy contract with Skat Foundation funded by WSSCC)

Chaiwe Mushauko-Sanderse BSc. NRM, MPH
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  • awhitesell
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Re: Sludge pumps with better valves?

Hi Chaiwe,

Regarding the problems you encountered with the Gulper: I experienced the same four issues in Nairobi. 

Could you describe your experience with the eVac and the Flexcavator?

I don't agree entirely with the excerpt from the extract that says "It is not fair blaming the pumps failing to handle the plastic but it is an immediate effect of its...". I believe that an appropriate solution should address known and significant performance issues. Of course, the engineers developing the pumps need to make compromises and every solution will not work under all conditions. And lessons can be learned from each of the pumps developed and tested. But I don't think we pump developers should simply accept that plastic bags need to be manually removed prior to pumping, we just need to do better - if a sustainable and safe FSM business model precludes manual bag removal then a proper solution should be the developed (with all the normal caveats: i.e funding is available, the solution is economically viable, it is reliable, etc.).

Best Regards,

Andrew
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  • Chaiwe
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Re: Sludge pumps with better valves?

Dear Andrew,

It is quite interesting to hear that your experiences in Nairobi were similar. I honestly think that the Gulper needs a lot of work before we can even begin to consider it as a workable option for pit-emptying within many Sub-saharan Countries that do not commonly use wet pits.

Regarding the eVac and Flexcravator, both of which are compact mechanised pumping systems, my observations can be summed up as follows based on the Lusaka experience:

i. Both technologies easily maneuvered their way around tight spots and narrow streets
ii. Access to the containment wasn't as challenging as the gulper, with fewer occasions were the interface needed to be broken to allow access or a door or roof removed. 
iii. The evac especially seemed to have fewer problems with regards to blockages resulting from solid waste, less so than the flexcravator whose trash exclusion systems (auger) failed miserably (newer versions have since been developed and so it would be great to hear if some of the issues experienced in Lusaka have been addressed)
iv. Both technologies required the use of a power source, this is already a major problem for many informal settlements where power supply is erratic.
v. solid waste fishing was still an occurrence, but minimal in comparison to the gulper and less so in the case of the eVac.

I think to respond to your concern, i quote:

But I don't think we pump developers should simply accept that plastic bags need to be manually removed prior to pumping, we just need to do better 

The most positive outcome of the testing was that the solid waste problem is not a problem for the technology developer alone, but is a toilet standards development problem, that needs to address ways of preventing/ limiting the user from dumping waste into the pit. It is also a solid waste management and service problem.  

Regards,
Chaiwe
Co-moderator SuSanA forum
(Under consultancy contract with Skat Foundation funded by WSSCC)

Chaiwe Mushauko-Sanderse BSc. NRM, MPH
Independent consultant located in Lusaka, Zambia
Email: This email address is being protected from spambots. You need JavaScript enabled to view it. Twitter: @ChaiweSanderse

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  • dandreatta
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Re: Sludge pumps with better valves?

It seems to me that the problem with sludge pumps, with or without better valves, is that they don't have a lot to offer beyond the simple scoop.  In Nairobi my pump was 25% faster than the simple scoop when filling buckets, but there is the additional hassle of transporting the pump, setting it up, getting it primed, and then cleaning it when finished. 

I've considered adding a gearmotor to the pump, but then you have the problem of finding power or bringing a generator.  Also if you make the pump faster then there is some other bottleneck in the transportation system.  At one point even with the hand powered pump I was filling buckets faster than they could be carried to the sludge cart by the two-man team.  

The valves in my pump pass soft trash well, and usually hard trash also, but it would still probably clog a few times per day, usually at the inlet.  The clogs are usually pretty easy to clear, but this is still time and effort spent that would not happen with a simple scoop.  

My pump would prime easily as long as the lift wasn't more than a meter and as long as the sludge was pretty thin, but those are all hassles that don't come up with a simple scoop.  

In short, the simple scoop is so versatile, and reliable, and low in cost, and easy to transport, it's tough to beat.  

Dale Andreatta
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  • Chaiwe
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Re: Sludge pumps with better valves?

Hello Dale,

I had a little chuckle at this statement below, Probably because I have never heard it put quite like that. I strongly agree!  It is a thought at the back of everyone's mind without actually voicing it. 

In short, the simple scoop is so versatile, and reliable, and low in cost, and easy to transport, it's tough to beat.  

Allow me to share this beautiful photo of the scoop in action taken out of this   publication 'The Heroes Behind Sanitation'


Regards,
Chaiwe
Co-moderator SuSanA forum
(Under consultancy contract with Skat Foundation funded by WSSCC)

Chaiwe Mushauko-Sanderse BSc. NRM, MPH
Independent consultant located in Lusaka, Zambia
Email: This email address is being protected from spambots. You need JavaScript enabled to view it. Twitter: @ChaiweSanderse

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  • jocetsai
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Re: Sludge pumps with better valves?

Hi Andy and Dale -  It’s good to see colleagues addressing this persistent problem.

Outside of “fishing”, there are two ways to approach the problem of trash. One method is to have it removed entirely by the pump. NC State via the Flexcrevator and Excluder has taken the trash exclusion approach, where trash doesn’t enter the pump in the first place. We presented our design at FSM5 and have outlined the benefits of method (see FSM Presentation, 5thslide). Trash exclusion eliminates “fishing”, makes downstream treatment easier, opens opportunities for people to use trash-free sludge as resource, and potentially allows simpler, stand alone pumps to do the job (not big vacuum trucks). By separating the trash from the sludge, it also emphasizes to the end user that the trash shouldn’t be thrown in the pit in the first place.

As we talk partners using our device we do hear that customers do want everything removed. However, we’ve seen that some customers are willing to pay extra for trash removal if they see sludge and trash removed separately. When our Madagascar partners tested the Excluder, the pit emptiers were able to charge an extra amount to remove the trash after the fact. This shows that this technology has the promise to inspire behavior change, as customers may want to avoid throwing trash in the pit in the first place.

As Chaiwe mentioned we have been in this space for a while and encountered some difficulties in Zambia ;) . Our FSM presentation walks through our many improvements since the version tested in Lusaka. We’ve also tested since tested in Kenya, Rwanda and Madagascar. Each location has given us more insight on how to make the design more robust and better equipped to handle plastic bags and cloth. Our most recent set of updates have been made on the Excluder portion (see Marketing Materials). Since Zambia we’ve made the device a modular pipe that can be easily inserted into the pit. The new head design also screens out and clears the trash. We’ll be performing market and field tests in Ghana this year (COVID-19 permitting) and look forward to updating you all on our progress.

In the meantime, Andy and Dale, if you do find a good solution for valves that help with pumping trash please do share it. Trash in pits is a difficult problem and we all benefit from multiple solution sets. 

Jocelyn Tsai

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  • awhitesell
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Re: Sludge pumps with better valves?

Chaiwe wrote:
The most positive outcome of the testing was that the solid waste problem is not a problem for the technology developer alone, but is a toilet standards development problem, that needs to address ways of preventing/ limiting the user from dumping waste into the pit. It is also a solid waste management and service problem.  


Hi Chaiwe,

I definitely agree that focusing on pumps is an insufficient approach to solving the problems associated with collecting human waste. The toilet, the storage means, the service models, and household practices all need to be improved. But, I remain optimistic that suitable pumps can be developed that will make the emptying more hygienic, safer, faster, and profitable.

AW
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Re: Sludge pumps with better valves?

dandreatta wrote: It seems to me that the problem with sludge pumps, with or without better valves, is that they don't have a lot to offer beyond the simple scoop.  In Nairobi my pump was 25% faster than the simple scoop when filling buckets, but there is the additional hassle of transporting the pump, setting it up, getting it primed, and then cleaning it when finished. 

I've considered adding a gearmotor to the pump, but then you have the problem of finding power or bringing a generator.  Also if you make the pump faster then there is some other bottleneck in the transportation system.  At one point even with the hand powered pump I was filling buckets faster than they could be carried to the sludge cart by the two-man team.  

The valves in my pump pass soft trash well, and usually hard trash also, but it would still probably clog a few times per day, usually at the inlet.  The clogs are usually pretty easy to clear, but this is still time and effort spent that would not happen with a simple scoop.  

My pump would prime easily as long as the lift wasn't more than a meter and as long as the sludge was pretty thin, but those are all hassles that don't come up with a simple scoop.  

In short, the simple scoop is so versatile, and reliable, and low in cost, and easy to transport, it's tough to beat.  

Dale Andreatta
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Hi Dale,

I believe that pumps have the potential to offer much more that scoops or buckets - that properly designed pumps (various types need to be developed) can offer hygienic and fast emptying. For example, the third generation pump we developed was capable of emptying septic tanks at 3 liters/sec and functioned to a depth of 4 meters. And it could be used without waste being spilled around the worksite. 

Thicker sludge presents more challenges but I think there is a solution out there.

I agree that simpler is better but as the adage goes, "as simple as possible, but no simpler". The scoop is certainly simple but when stricter requirements are imposed, it may be too simple.

Cheers,

Andrew
Andrew Whitesell
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