Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

  • awhitesell
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Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

Hi All,

This topic is being started in response to some inquiries and discussions about performing latrine-pit and septic-tank fill-rate studies. As the number of people in the email chain grew, we decided to shift it to this forum so others could contribute and the knowledge disseminated. Steve Sugden, Chris Buckley, and Jamie Radford have volunteered (or have been volunteered) to contribute some of their wisdom (and anecdotes).

Hopefully, by making previous research readily available and discussing the pro's and con's of the studies, reviewing the procedures and data collected, and refining the study design and methods, future efforts can build upon the existing work. Ideally, future studies, done by different groups in different parts of the world will tend to be more similar than different and the data collected more easily shared and compared.

A good place to start will be posting the work that has been published to date. As far as I know, there haven't been many studies so it shouldn't take long to compile them. I think it would be great if some of the SuSanA subscribers could review the documents and begin discussing them on this thread. It would be fantastic if authors of the documents contributed some insights about the work that was performed as well. I'm sure there are a few goods stories to be told.

Anyone thinking about doing a vault fill-rate study is encouraged to describe their objectives and relevant information about their study design, the tools they will use, and how the data collected will be managed and shared. What data is collected and what tools are used are topics that I know Jamie and Steve have opinions on. I'm going to start separate discussion topics about some of the other data that might be collected in parallel to the fill-rate (vault contents, shear strength) and tools that might be employed. Their topic titles will be:
  • Vault Content Research [Fill-Rate Measurement]: Measurement methods and tools
  • Vault Content Research [Debris & Heavies]: What’s in there besides human waste
  • Vault Content Research [Mechanical Properties]: Measurement methods and tools
  • Vault Content Research [Pathogens]: Past/Current & Planned
  • Vault Content Research [Chemical Properties / Energy Content]: Measurement methods and tools
  • Vault Content Research [Data Acquisition, Database, Data Analysis]: Tools & Best Practices
I’m not sure if these discussions will gain traction or not: Some are certainly covered elsewhere on the forum and some may not merit their own thread.If it becomes necessary, I’ll create some google docs to keep information consolidated and easily accessed.

Jamie has suggested the following over-arching objective of the Vault Content Research threads:

To reduce the whole-life cost of safe latrine use [i.e. including emptying and FSM] for households by improving the equipment used and the services provided.

Andrew Whitesell
President/Founder of Beaumont
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  • awhitesell
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Re: Vault Content Research [Fill-Rate Measurement]: Measurement methods and tools

This thread is part of a multi-threaded topic: Vault Content Research

Anyone who has done a vault fill rate study, plans to, or has ideas about fill rate measurement methods and tools is invited to add content.

Cheers,

Andrew

Andrew Whitesell
President/Founder of Beaumont
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  • muench
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Re: Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

Dear Andrew,

Thanks for taking the initiative for this! I really like that you decided this:

As the number of people in the email chain grew, we decided to shift it to this forum so others could contribute and the knowledge disseminated.


That's exactly what the forum is for. :-)
I have now created a sub-sub category under the faecal sludge management category for this topic on vault content research to keep it all together.

However, I would question the use of the term "vault" for this (I think I have mentioned this already elsewhere on the forum somewhere):

Isn't a vault something that is "closed"?
(I checked on Wikipedia and there is a range of definitions for vault: en.wikipedia.org/wiki/Vault - none of them have anything to do with a pit where content leaches out)

Vault is OK for a septic tank or for a urine-diverting dry toilet (which has a faecal matter vault), but for a pit latrine? Is a pit really a vault? Perhaps it's different for a native English speaker than a second-language English speaker like myself. Could you please explain your decision to use vault for both things? Thanks.

Why not "Pit and septic tank content research"? (apart from the fact that it would be longer)

Regards,
Elisabeth

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  • awhitesell
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Re: Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

Hi Elisabeth,

I tend to use the word vault as latrine pits implies “dry” pits and septic tank implies a “wet” tank. In the case of pump development, this can be misleading as a septic tank might require a pump that can pump thick or even dry material typically found in a latrine pit. So I’ve gotten accustomed to referring to wet and dry vaults and not identifying what the construction technique is.

For the purpose of pump development, we have defined Wet and Dry Vaults as follows:
  • Wet Vault: contains material with a concentration of 0-5%TS or a shear strength of less than 400Pa
  • Dry Vault: contains material with a concentration of 10-40%TS or a shear strength of 1000-5000Pa
Material that falls in between those two can be pumped by a FSOI pump suitable for dry material or water can be added to allow a wet vault pump to handle it. Vaults containing material with a shear strength higher than 5kPa are considered dysfunctional or neglected and the FSOI pump developers were not required to design for material that strong.

Cheers,

AW

Andrew Whitesell
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  • stevensugden
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Re: Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

Thanks Andrew for starting this process. Much has already been posted on Susana and the knowledge vaults will hopefully start to fill up soon.

It is important that we move away from subjective descriptions of pit / vault contents, particularly with regard to fill up rates and the effectiveness of pit emptying devices. Without the ability to accurately assess and measure, our understanding of the vault / pit processes will never improve and debates about which this the best machine and assessments of fill up rates will be all smoke and mirrors quackery.

If a Wet Vault = a shear strength of less than 400Pa and a Dry Vault = a shear strength of 1000-5000Pa. How should we class a range of 400Pa to 1000Pa? Are two categories enough? Anything over 1500 Pa would seem unpumpable, whereas 1000 Pa achieveable.


The vault/pit is first place on the sanitation value chain and anything that happens here will have an exponential beneficial knock-on impact to all other parts of the FSM chain. In many respects it is the most important part of the chain and I'm puzzled, and to some extent frustrated, over the lack of progress we are making in developing better tools. Jamie Radford's Ball Penetometer may not be the final solution, but at the moment it is the only accurate tool available and we should all be work together to make it more robust, easier to use and widely available. It should be part of our standard tool kit in much the same way the Delagua kit is part of the water quality testing arsenal.
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Re: Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

Hi Steve,

I agree wholeheartedly that better information is needed. With regards to pumping systems, which has been a major focus of the Omni-Ingestor project, quantifying the effectiveness of the pumps being developed is only one piece of the puzzle. Without a good understanding of what is being pumped, the pumps will inevitably be under-designed or over-designed. And while engineers typically shoot for over-designing (Unless you are Colin Chapman), that can lead to products that are more costly than they need to be. Or, they could be heavier than they need to be which is also problematic. Without data from multiple countries / cities / communities, the products might be suitable for one region and not another. And with good data, it might be determined that more than one or two types of pump are absolutely necessary. I think your point, and mine, is that the research has more than academic value and can drive product development and service decisions.

With regards to my definition of Wet and Dry Vaults: it’s something that I’m not entirely comfortable with. I defined it in the context of pump development and was attempting to provide the pump developers with clear goals about what their pumps had to achieve. I didn’t want to make the range so broad that it would complicate the design of the pump and make them too costly. Furthermore, the Omni-Ingestor is intended to include a sludge-thickening subsystem capable of dewatering the influent to 10% solids. Watery sludge thickened to 10% solids can be efficiently transported. Concentrating it beyond 10% adds costs and diminishing economic value. So the thinking was, Wet Vaults (typically septic tanks) which are unlikely to contain material approaching 5%, will be emptied with one type of pump and the system will include sludge-thickening. Dry Vaults would be emptied by pumps that can handle material that is unlikely to be lower than 10% solids and no sludge-thickener would be needed. I didn’t bother defining the material in-between as it didn’t appear at the time, that we would encounter it very often and when it was encountered, the Dry Pump could be used or it could be diluted and the Wet Pump used.

Up till now, my definition of Wet Vaults and Dry Vaults has only been used by those of us working on the OI project. It was originally based on %TS alone with shear strength being added later. As such, the cut-off points for the shear strength may not be appropriate. In any case, it can certainly be refined. Maybe, as more shear strength data comes in, we’ll see that there aren't two distinct bell-curves and need to redefine it. And maybe there are other factors we’ll want to include in the definition.

Cheers,

AW

Andrew Whitesell
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  • Freya
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Re: Vault Content Research [Fill-Rate Measurement]: Objectives, Study Design, Methodology, & Analysis

Dear Andrew and others,
Just adding some information to your discussion on sludge accumulation and pit emptying from studies I have been involved in with WSP and ADB in Indonesia. Although you say there hasn’t been much research, I know there have also been studies in the region by AIT and Eawag/Sandec.

Terminology: “On-site sanitation systems” is used to describe all types of pit latrines and septic tanks in Indonesia since there are a variety of designs (typically not a standard 2-3 chamber sealed septic tank) and can be both wet or dry depending on groundwater level and whether they are fully sealed (most are not). For context: most toilets are squat toilets with goose neck water seal and flushed using a bucket, anal cleansing is typical and most systems only receive blackwater.
Measurement methods: Measure thickened bottom sludge and water levels inserting a pole into the access lid of on-site systems (from unlined pits to concrete septic tanks). Measured the system size and recorded details of the design, outlet/discharge, surrounding groundwater level and soil type, and surveyed household about age, emptying history, number of users, etc. Calculated fill rate based on the thickened bottom sludge depth which was typically a discernibly more dense layer although some newer/smaller/recently emptied systems has no discernible settled sludge. Access to systems was the biggest challenge as most did not have lids.
What’s in there: Only fecal matter, blackwater only no greywater, and very little rubbish (occasionally strips of material used for MHM, no toilet paper or general rubbish).
Properties: Not measured in this study. Another study for ADB used local laboratories to analyse the sludge characteristics (BOD, COD, TS, VS) from samples collected as sludge trucks discharged to the treatment plant. Uncertain about the quality of analysis by the local laboratories since they had limited experience in wastewater analysis and no experience in FS analysis. Strength and other properties were not measured- current government and private sector emptying service providers typically use vacuum pumps which can empty all but the very dry pits, occasionally it was necessary to stir or add water to pump.
Comments on analysis: Although useful to know, sludge filling rates do not have a significant influence on designing faecal sludge emptying programs. Since both settled sludge and wet contents are emptied, the size of the system rather than settled sludge volume is more useful for designing sludge treatment. However the low accumulation rate compared with size of pit clarified why demand for emptying is low in Indonesia. And data collected about emptying frequency, reasons for emptying, and the realisation that most systems were leaking single pits have been valuable outputs from the study.

The abstract of the sludge accumulation study presented at the WEDC 37 conference can be found at: www.google.com/url?sa=t&rct=j&q=&esrc=s&...oTu9nqcKVmUDU-UY8YpA

Happy to discuss methods and results further or answer any questions regarding the conditions found in Indonesia.

Kind Regards
Freya Mills
Sanitation Consultant
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