What can we reliably say about pathogen removal with vermifilters?

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What can we reliably say about pathogen removal with vermifilters?

I've started a discussion about pathogen removal with vermifilters with Dean offline and he rightly pointed out to rather move our conversation to the Forum. So here it comes:

It started by me questioning how pathogen removal is described in the Wikipedia article about vermifilters, see here:
en.wikipedia.org/wiki/Talk:Vermifilter#Pathogen_removal.3F

Currently it says ( en.wikipedia.org/wiki/Vermifilter#Overview )

As a result of oxidation reactions, biodegradation and microbial stimulation by enzymatic action, organic matter decomposition and pathogen destruction occur in the vermifilter. A vermifilter may have removal efficiencies for Biochemical Oxygen Demand (BOD5) more than 90%, Chemical Oxygem Demand (COD) more than 85%, Total Suspended Solids (TSS) more than 98% and NH4+ more than 75%. It is possible to eliminate fecal coliforms to 2.0 Log10 of Most Probable Number (MPN) per 100 mL−1.[6]


I said about that:
But it's not a very good reference. It says submitted, has no year and no URL. Do we not have a better one? Also, this means nothing to a lay person: "It is possible to eliminate faecal coliforms to 2.0 Log10 of Most Probable Number (MPN) per 100 mL−1". Can it be simplified and wikilinks added? For example 99% removal. Also, do we need this overly scientific way of writing with the -1 in the superscript? Why not just mg/L (also in another place where that reference is used). If we talk about pathogen removal it would be good to have more information than just fecal coliform count. Let's not raise too high expectations, it's not a process for disinfection... (it doesn`t need to be either)

Dean replied:
Aren't fecal coliforms used to as a representative measurement for pathogens in general? Then there are helminths which might be a "can of worms".

Then I replied to him by e-mail:

++++++++++
There are these three previous threads where we spoke about indicator organisms which you might find interesting:

forum.susana.org/component/kunena/34-uri...-research-parameters

forum.susana.org/component/kunena/174-sa...or-reuse-or-disposal

forum.susana.org/component/kunena/207-de...asurement-techniques

When it comes to wastewater treatment, fecal coliforms is the commonly used indicator organism. For fecal matter treatment though it is more the helminth eggs that are important and relevant.

I think we need to get this straightened out in our Wikipedia article. If we don’t have good information about pathogen removal then we should not say anything much about it (and not raise unrealistic expectations). It is unlikely to remove more pathogens than other similar treatment methods like trickling filters or constructed wetlands, or is it?

It’s a pet hate of mine when technology providers promise the earth (“really high pathogen removal”) but have no data to back it up. I haven’t looked into it, but I wonder what the tiger worm toilet or the Biofil toilet people say about this.


+++++++++

This is how far we got. Now we are moving this to the Forum so that more people can benefit.

Regards,
Elisabeth

P.S. I was in two minds if I should post about it here in the category on vermifilters or in the existing thread about the Wikipedia article on vermifilters ( forum.susana.org/component/kunena/198-wi...ongoing-improvements ).

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Re: What can we reliably say about pathogen removal with vermifilters?

Just thinking a bit more about my own question:
We should probably distinguish between the type of wastewater to be treated with the vermifilter, e.g. relatively dilute domestic wastewater, or very concentrated blackwater from a toilet with a microflush system.

Secondly, when we talk about pathogen removal, there are two mechanisms:
  • One is just transfer from the liquid phase to the sludge phase. This could easily happen to the quite large helminth eggs that get filtered out from the liquid via the filter medium.
  • And the other is actual pathogen destruction - e.g. via been "eaten" and digested by the earthworms?
This is also something that is explained here on Wikipedia (the text was written by myself and others):
en.wikipedia.org/wiki/Helminths#Removal_...and_sludge_treatment

Removal versus inactivation in wastewater and sludge treatment[edit | edit source]

In order to physically remove (but not inactivate) helminth eggs from wastewater, processes that remove particles, such as sedimentation, filtration or coagulation-flocculation are employed.[31][32] Therefore, waste stabilization ponds (lagoons), storage bassins, constructed wetlands, rapid filtration or upflow anaerobic sludge blanket (UASB) reactors can be used. These conventional wastewater treatment processes do not inactivate the helminth ova but only removes them from the wastewater and moves them to the sewage sludge.

Helminth ova cannot be inactivated with chlorine, UV light or ozone (in the latter case at least not with economical doses because >36 mg/L ozone are needed with 1 hour contact time).
Inactivation of helminth ova can be achieved in sewage sludge treatment where the temperature is increased over 40 °C or moisture is reduced to less than 5%.[10] Best results can be obtained when both of these conditions are combined for an extended period of time.[33] Details about the contact time under these conditions and other related environmental factors are generally not well-defined for every type of helminth egg species.[7] Helminth eggs are considered highly resistant biological structures.[10]


Regards,
Elisabeth

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Re: What can we reliably say about pathogen removal with vermifilters?

Does a vermifilter commonly include a sludge reuse or discharge to surface water component where pathogens can come in contact with humans again? I think not, so this isn't really much different to pit latrines or simple septic tanks for which there is at most some concern about ground water pollution.

As far as I remember from the literature, it is generally assumed that the digestive action of the worms does not have a really significant or consistant effect on most pathogens, so I guess it is best to assume that there is little pathogen destruction other than generally due to the retention time in the system.

So to summarize, I think it is best to leave it as a general short statement as a vermifilter's purpose isn't really pathogen removal.

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Re: What can we reliably say about pathogen removal with vermifilters?

Hi Elisabeth,

Unfortunately pathogen "removal" isn't black and white... it involves dynamics that determine % removal based on filter volume, size of media, how well aerated it is, temperature and influent volume per unit of time. All other things being equal, hydraulic retention time has a solid relationship with removal of pathogens in vermifiltration and this can be increased by recirculation. This is all in the literature.

I don't think we need to get hung up on removal levels for fecal coliforms in wastewater, just that removal can be customised to the level required. The application would determine the required level and design would be for that level. For example discharge to waterways requires a higher level of removal than discharge to soil. Discharge to food crops requires a higher level of removal than discharge to non-food crops (see WHO guidelines). Vermifiltration can provide whatever level required, again this is only a design issue... much like capacity in a DEWATS.

We can be certain that helminths can be physically removed to 100% from the wastewater using vermifiltration. This is in the literature. That they might remain active in the humus is in my mind a moot point because it is the liquid effluent that contains high quantities of plant nutrients and therefore needs to be free of helminth ova for irrigation to food crops (to break the helminth cycle and complete the nutrient cycle). We also know that over time helminth ova lose viability in any substrate... including humus. Whether it is 3 years or 5 years before they are gone completely might remain a question until someone does the research and provides the answer... meantime we can rest the humus to be sure it is free of nasties. Otherwise just use it around trees.

The Gates Foundation funded three separate recipients with grants looking into solving sanitation issues around vermifiltration toilets. Elisabeth, would you be able to dig up the grant applications and the promises therein for:
  • Biofilcom;
  • GSAP; and
  • Bear Valley Ventures?
I'm interested in whether any of these projects were going to look into levels of helminth ova in humus generated from vermi-digesters? Keep in mind the effluent is directly disposed to land in all these models (to soakaways) ...therefore they are not designed for pathogen destruction/helminth removal, whereas the humus builds up over approx 5 years and then has to be removed. So how safe is it and should users know what they can do with it?

cheers

Dean

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Re: What can we reliably say about pathogen removal with vermifilters?

Thanks for your replies, Kris and Dean.
I tend to agree with Kris who said:

"So to summarize, I think it is best to leave it as a general short statement as a vermifilter's purpose isn't really pathogen removal."

Or perhaps what's happening is that pathogens are transferred from the liquid phase to the sludge/humus phase where they are more contained and easier to handle with a multiple-barrier approach.

Dean, you asked:

The Gates Foundation funded three separate recipients with grants looking into solving sanitation issues around vermifiltration toilets. Elisabeth, would you be able to dig up the grant applications and the promises therein for:

Biofilcom;
GSAP; and
Bear Valley Ventures?


Good question! From memory, none of the three specifically focused on pathogen removal. One reason might be that the test for it can be relatively expensive, e.g. measuring helminth eggs. Or that it wasn't their main research objective.

But I might also be mistaken. To find the information about these three grants that's been shared with the SuSanA platform so far, you can look them up in our project database:
www.susana.org/en/resources/projects

So for example Biofilcom: Despite my best efforts, I haven't been successful to get them to share information on the SuSanA platform. The only thing I was able to collect so far is a powerpoint presentation, see here: www.susana.org/en/resources/library/details/2288

The GSAP project is headed by Steve Mecca and he's been very active here on the forum which is great. The grant description is here on the Forum:
forum.susana.org/forum/categories/106-us...roject-usa-and-ghana

I will also send him an e-mail to alert him to this thread.

Bear Valley Ventures we've also had on the forum. The easiest way to find it is to put "bear" into the search field of the project database which brings up these links:
www.susana.org/en/resources/projects?search=bear

Walter Gibson is the main person behind Bear Valley Ventures. He and his team have put out several publications, perhaps it says something about pathogen removal there. I'll also send him an e-mail now.

All the threads about these vermi-digester type toilets are available in this sub-category on the forum:
forum.susana.org/290-vermifilters-for-bl...ts-tiger-worm-toilet

Regards,
Elisabeth

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Re: What can we reliably say about pathogen removal with vermifilters?

The question of pathogen removal in vermi- or other macro-organism systems has been ar0und for some time. Last year a colleague of mine (her ares is microbiology), I and a student researcher began a project to track the bacterial census using 16S rRNA analysis for the solid and filtrate products in a GSAP Microflush toilet's filter-digester. The project is nearly complete and we expect to submit a paper in early summer. Such tracking doesn't show kill of a bacteria (as the DNA of dead bacteria also gets recorded) but the overall census does show characteristics moving away from fecal sludge. Stay tuned for the final results/paper. I think the results will change some thinking on the matter of vermiculture's impact on pathogen removal.
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Re: What can we reliably say about pathogen removal with vermifilters?

A large and increasing body of literature is dedicated to studying pathogen removal in vermifilters because this is their primary purpose. Sure, the wikipedia article should not be a literature review, but references are available and abundant to validate statements made in the article.

Or perhaps what's happening is that pathogens are transferred from the liquid phase to the sludge/humus phase where they are more contained and easier to handle with a multiple-barrier approach.


Firstly, lets not call the solid phase sludge please. In a vermifilter there is fecal material and there is humus, but no sludge.

Secondly, yes for helminth eggs, but no for pathogens. I haven't found anything in the literature that convinces me that helminth eggs are destroyed in the humus, but they certainly are removed from the wastewater (100%). The importance of this is that the wastewater can be rendered safe for use in irrigation and is rich in nitrate because of the aerobic process. The humus? Well, again, we do know that over time helminth eggs break down. Seems that nobody has studied the rate of helminth reduction for resting humus in a vermifilter. In my view this is a huge gap and a clear research priority given that waste digester vermifilters have been commercialised in developing countries. For example the wikipedia articles states that "... is now being marketed commercially in India where over 2000 of these toilets and treatment systems had been sold and installed by May 2017." The research paper (2016) that preceded the hurried commercialisation phase in India stated "vermicompost is a valuable product" and "The next challenge is to make a scalable and economically viable prototype for this market." Cart before the horse? What is the vermicompost used for? I trust not for food crops...

As for pathogens, there are many studies showing significant reduction in pathogens (represented by fecal coliforms). Sure, these are certainly being physically removed by the filter in that the fecal material (which contains most of the fecal coliforms) is being retained, but much more than that is happening in the vermifilter. It is a biological reactor and that fecal material is rapidly broken down and reduced to mostly liquid which exits the reactor. The macro- and micro- organisms break down the pathogens, so they are actually being reduced in numbers through biological processes. So how are these measured?

On 15 May Elisabeth removed this from the vermifilter article:

It is possible to eliminate fecal coliforms to 2.0 Log10 of Most Probable Number (MPN) per 100 mL−1

...apparently because the terminology is too "technical". However these numbers came from a referenced scientific publication and did quantify the removal of pathogens as fecal coliforms.

From International journal of Environmental Science and Technology · March 2017
Is filter packing important in a small-scale vermifiltration process of urban wastewater?

"Guidelines for wastewater reuse in irrigation indicate a pH between 6.0 and 9.0, a BOD5 concentration B10 mg L-1 (for food crops consumed uncooked) or B30 mg L-1 (for non-food crops and food crops consumed after processing), a TSS concentration between B30 mg L-1 (for processed food crops) and, for fecal coliforms and helminth eggs, a maximal MPN of 103 100mL-1 (or 3.0 Log10) and 1 unit L-1, for agricultural irrigation (USEPA 2004).

For pathogens only, WHO (2006) indicates a maximum MPN of 103 100 mL-1 (for unrestricted use), a maximum MPN of 104 100 mL-1 for restricted use and B1 No. L-1 for helminth eggs."


You will see that both WHO and USEPA guidelines use MPN to quantify fecal coliforms. If the reduction in fecal coliforms is not to be expressed this way in the wikipedia article, then how should it be expressed? Simply removing the quote is not appropriate, it would need to be replaced by better wording. In my view MPN is the right quantity.

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Re: What can we reliably say about pathogen removal with vermifilters?

As promised, I have e-mailed Walter Gibson from Bear Valley Venture about this question of pathogen removal and here is his e-mail response:

+++++++++

Dear Elisabeth,

Thanks for letting me know.

Please refer your readers to the paper in Waterlines which is open access at www.developmentbookshelf.com/toc/wl/35/2 .

This has all the data we generated from a one year field trial of the Tiger Toilet in India, including pathogen removal , where we found a 2 log reduction in thermotolerant coliforms. The trial was a partnership between BVV and Primove Infrastructure Development Consultants and was funded by USAID.

I hope that helps,

Kind regards

Walter

+++++++++

The paper that he referred to is this one (open access):
www.developmentbookshelf.com/doi/abs/10.3362/1756-3488.2016.013

Technical and user evaluation of a novel worm-based, on-site sanitation system in rural India
C. Furlong et al., May 2016

Abstract
The technical performance and user acceptance of a novel on-site sanitation system based on vermifiltration was tested for over 12 months in rural India. Ten households (mean household size = 5.6 people) who had previously practised open defecation trialled a pour flush toilet linked to a vermifilter, together known as a ‘Tiger Toilet’. Technical parameters which were monitored over this period included: usage, temperature, accumulation of faecal matter and vermicompost, presence of worms, and influent and effluent quality. User satisfaction was evaluated relative to a baseline survey and through focus group discussions. The vermifilters processed human waste products effectively in a real life scenario. After 12 months there was little accumulation of faecal solids (0–10 per cent surface coverage) and effluent quality was good (chemical oxygen demand reduction = 57 per cent, faecal coliforms reduction = 99 per cent). Vermicompost accumulation was low and suggested that emptying would only be necessary every five years. User satisfaction levels were high, with 100 per cent of respondents being either very satisfied (60 per cent) or satisfied (40 per cent) with the ‘Tiger Toilet’. The main reasons given were the use of worms and the lack of smells.



Coincidentally, the same journal issue has another paper about tiger worm toilets by Oxfam (behind a paywall though):
www.developmentbookshelf.com/doi/abs/10.3362/1756-3488.2016.012

Furthermore:

Hi Steve,
thanks for your interesting forum post, looking forward to hearing the results from your research when they become available.

Hi Dean,
I'll respond to your specific points in a separate post by the end of the week. The specific parts about the wording for Wikipedia might be better discussed on the talk page of the article or in this forum thread: forum.susana.org/198-wikipedia/19903-art...ongoing-improvements (although I can also follow the reasoning for having it in this thread).

Regards,
Elisabeth

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Re: What can we reliably say about pathogen removal with vermifilters?

Hi Elisabeth, I can't seem to find the grant applications, the level of funding and what was promised.

My question for the three grantees was this:

I'm interested in whether any of these projects were going to look into levels of helminth ova in humus generated from vermi-digesters?


This was not a general question about pathogen removal at all, the literature is abundant and comprehensive on effectiveness of vermifilters for pathogen removal... but what about reuse of the "vermicompost" from digesting fecal material in vermifilters? Despite lots of grant money spent on "development" of the technology, we appear to still know nothing about helminth content of the humus fraction that is removed from the vermifilter, or how this changes over time.

The question was not about the effluent quality from these three vermifiltration toilet products, because in my own words

the effluent is directly disposed to land in all these models (to soakaways) ...therefore they are not designed for pathogen destruction/helminth removal, whereas the humus builds up over approx 5 years and then has to be removed.


I repeat:

how safe is it (the humus) and should users know what they can do with it?

?

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Re: What can we reliably say about pathogen removal with vermifilters?

Hi Dean,

In response to your post just before this one, I would like to contribute this:

The grant applications are not in the public domain but the level of funding is. You can find it in this public database on the Gates Foundation website:
www.gatesfoundation.org/How-We-Work/Quick-Links/Grants-Database

I think it's nice and useful that they are making this information public.
The grant to Bear Valley Venture you won't find in there as it is a sub-grant from this grant to USAID:
www.gatesfoundation.org/How-We-Work/Quic...s/2011/06/OPP1029829

(8.5 Million USD "to support a collaboration with the U.S. Agency for International Development to support the identification, testing, and sustained uptake of evidence-based approaches to delivering water, sanitation and hygiene services to the poor ")

I tried last year to assemble outcomes from that grant to USAID and what I was able to gather is available here (I would have liked to gather more but some of the grantees had no time to respond):
www.susana.org/en/resources/projects/details/130

Secondly you said:

Despite lots of grant money spent on "development" of the technology, we appear to still know nothing about helminth content of the humus fraction that is removed from the vermifilter, or how this changes over time.


From what I gather, indeed, the grantees did NOT focus on the solids/fecal/humus fraction of these "tiger worm toilets" but rather on other aspects. I can understand why that decision was taken. Whilst it would have been interesting from a research point of view, it may not be critical from an upscaling and commercialisation point of view. Why do I say that? Because firstly, the solids accumulation is so slow that it takes years before anyone has to empty that out. When it's being emptied out, it can be done safely so that nobody comes in touch with the stuff and could get infected with the helminths. It might indeed be best to have a service provider rather than let the household people do it themselves? Either way, if we can empty out pit latrines safely (with the right service provider, personal protectic equipment etc.), then we can also empty out these vermifilter digesters.

It's all about risk management and a multiple barrier approach, i.e. what do you do with the stuff aftewards? I would say burying or at least covering under some soil to prevent direct content.

The multiple barrier approach is key here, it is the one propagated in the WHO Guidelines from 2006. You can also read up about it on Wikipedia here:
en.wikipedia.org/wiki/Reuse_of_excreta#M...e_use_in_agriculture


Now I want to reply to your points in your earlier post from 17 May:

You said:

Firstly, lets not call the solid phase sludge please. In a vermifilter there is fecal material and there is humus, but no sludge.


Point taken although doesn't the material look like sludge to a lay person? I agree we shouldn't call it fecal sludge but it is a type of sludge, isn't it? Could you post a photo to remind us what it looks like?
Or perhaps the first photo here is a good example?: en.wikipedia.org/wiki/Vermifilter



Then you said:

Secondly, yes for helminth eggs, but no for pathogens.


Not sure if this wording was a slip of tongue or on purpose, but helminth eggs are part of the pathogens!

You said:

Well, again, we do know that over time helminth eggs break down. Seems that nobody has studied the rate of helminth reduction for resting humus in a vermifilter.


Those helminth eggs are actually extremely hardy. E.g. they can survive in soils for years, even at low moisture level. They just go into some kind of dormant state...
I was involved in summarising information on Wikipedia here (although reading it again, it still needs to be made easier to understand):
en.wikipedia.org/wiki/Helminths#Eggs
Would love it if a helminth egg expert could help with editing that article!

You said:

The research paper (2016) that preceded the hurried commercialisation phase in India stated "vermicompost is a valuable product" and "The next challenge is to make a scalable and economically viable prototype for this market." Cart before the horse? What is the vermicompost used for? I trust not for food crops...


I semi agree with you. I think the users should not be given a false sense of security: the vermicompost should not be marketed as "pathogen free" unless we know that it is. Until then, the toilet owners should be advised to treat that product with considerable care. As I said above, it is probably best if certified service providers empty the vermidigesters. But as emptying is only needed so rarely, I don't see this as a big drawback. Although maybe we'll run into the same problem as we did with filled pit latrines: users abandon them rather than getting them emptied (?).

So I guess it's a fine line: you want toilet owners to be aware that there are likely still helminth eggs in that humus and you want them to be careful but you don't want them to be so scared that they wouldn't dare to empty the digester themselves if needed (like if no service provider is available or too expensive or not convenient).

I would like to hear from those who are operating or selling these kinds of toilets, what are their experiences with the humus/solids/sludge? Or is it taking so long to accumulate that there are no emptying experiences yet?

Lastly about that wording for the Wikipedia article, you said:

It is possible to eliminate fecal coliforms to 2.0 Log10 of Most Probable Number (MPN) per 100 mL−1 - If the reduction in fecal coliforms is not to be expressed this way in the wikipedia article, then how should it be expressed?


I would say this kind of sentence says pretty much the same thing but is more easily understood by a lay person and therefore better:
"In the effluent there was a 99% reduction in fecal coliforms."

Don't you agree? (I am in two minds if it's better to discuss this Wikipedia issue here in this thread or rather in this thread: forum.susana.org/198-wikipedia/19903-art...ongoing-improvements I suppose it's fine to keep it together with the pathogen removal topic, i.e. this thread)

I always enjoy discussing vermifilters with you, Dean, and I hope that others who are reading our posts also get inspired to write in this thread, too - i.e. to the silent members, I would like to say: "please don't just read but also write!" :)

Regards,
Elisabeth

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Re: What can we reliably say about pathogen removal with vermifilters?

Walter Gibson (Bear Valley Venture) sent me another input by e-mail which I am copying below (I would say it is quite inline with what I said in my post just before this post):

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Hi Elisabeth,

I think the first thing to make clear is that we do not see the main purpose of the Tiger Toilet to be the production of compost for use on soil. In fact we have deliberately tried to minimise production of vermicompost so as to reduce the amount of maintenance for the user. Our current estimates are that it will be 8-10 years before any removal of vermicompost is necessary and the amounts involved will be quite small and not very useful to a farmer. Our oldest systems are over three years old and have not yet been emptied. The whole purpose of the Tiger Toilet is to provide safe, effective and low maintenance treatment of faecal waste for low income households ….we are not promoting re-use with this system.

We agree that there could be helminths present in the vermicompost and therefore would not advise using it as a soil conditioner without some kind of further treatment.

Kind regards,

Walter

Dr. Elisabeth von Muench
Independent consultant
Community manager of this forum via SEI
(see: www.susana.org/en/resources/projects/details/127 )
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