Hi Elisabeth,

I am aware that parasites are a subset of pathogens, but was looking for terminology that the layperson understands and can use to distinguish bacteria from parasites in the context of wastewater treatment. Unfortunately "pathogen" means something different to every person. I'll have to go with "bacterial pathogens" and "parasite pathogens" (Also "virus pathogens"). Or just "bacteria", "viruses" and "parasites" (like in the WHO guidelines) and not use the word "pathogens" at all.

From the WHO guidelines for the safe use of wastewater , excreta and greywater ( www.susana.org/_resources/documents/defa...water-vol4-part1.pdf ), dieoff of Ascaris (parasite) is 125 ⁺/_- 30 days in faeces and 625 ⁺/_- 150 days in soil. A big difference, so where does fecal humus sit?

This time-dependant reduction or elimination applies to other parasites also. Cryptosporidium lasts a long time, 70 ⁺/_- 30 days in feces and 495 ⁺/_- 182 days in soil. I'd note that "Cryptosporidium spp. oocysts were considered the highest prevalent parasite detected in raw vegetables" ( www.sciencedirect.com/science/article/pii/S2090506812000504 ) and "Cryptosporidium infection can be mediated via farm soil and vegetables" ( www.ncbi.nlm.nih.gov/pmc/articles/PMC4214936/) ).

Giardia, Hepatitis A, Rotavirus, E. coli and Salmonella are all pretty much gone in a couple of months.

If reuse in crops isn't important for sustainable sanitation and "sanitation" is only about getting rid of our waste using shortcut approaches (even if "better than pit latrines or open defecation") and dealing with the issues later, then the word "sustainable" should really be removed. This first world model is surely not appropriate for the developing world where resources such as fertiliser and water are limited. The reason why fresh vegetables continue to be riddled with pathogens is because farmers ignore multiple barrier approaches and continue to use the available resource (unsafe excreta) for their crops.

In the context of this discussion, the multiple barrier approach seems to me like a moot point. Relevant once, but now we finally have a technology that offers safe, low cost secondary treatment for re-use, a game changer because we don't need complicated multiple barriers any more, nor expensive secondary treatment, just a keep it simple approach... provided some simple design rules are followed:

• The fecal humus rests for the required time (only possible with a twn chamber vermidigester); and
• the effluent gets secondary treatment to remove helminth parasites for reuse - again vermifiltration.

cheers
Dean

Hi Dean,

(it's such a fascinating topic, how come nobody else is jumping into this discussion? Pity!)

You said:

perhaps by "other aspects" you allude to their business models.

Yes, pretty much. With your work in New Zealand you may not have come across first-hand the difficulties with sanitation provision in developing countries, like India (neither have I, only indirectly). It's hard for you and I to imagine but just getting people to move from open defecation to using a toilet that they like to use is really difficult! So I am assuming that the humus reuse question has a lower priority than the "demand creation", "market development" kind of stuff. (see also this recent webinar: ""Developing Markets for Sanitation: Where to Start?""
forum.susana.org/167-market-development-...d-further-discussion )

The Gates Foundation has funded an amazingly broad range of sanitation projects, some focusing on technology innovation, some on reuse, some on pathogen destruction, some on behavior change, some on market development...
I agree with you that these tiger worm toilets are not top notch in terms of environmental sustainability (I also worry about groundwater pollution from the leach beds), but if the users like them and are willing to invest in them then this is still better than pit latrines or open defecation.

Coming back to the issue of terminology, I disagree with you here:

When discussing treatment of wastewater I differentiate between pathogens and parasites. I consider helminths parasites rather than pathogens and would appreciate discussion in this forum using those terms to avoid confusion.

Helminths are parasites but helminths are also pathogens. "Pathogens" is the over-arching term to be used. This is what wastewater textbooks say. A pathogen is a disease-transmitting agent; therefore a helminth egg is definitely a pathogen.

This is also described quite clearly (I hope) in the Wikipedia article on sewage for example:
en.wikipedia.org/wiki/Sewage#Pathogens

After your last post I did a bit of work on it, digging out two main sources. I had this one handy from SEI:

Sewage contains human feces, and therefore often contains pathogens of one of the four types:[8][9]
- bacteria (for example hepatitis A, rotavirus, enteroviruses),
- viruses (for example Salmonella, Shigella, Campylobacter, Vibrio cholera),
- protozoa (for example Entamoeba histolytica, Giardia lamblia, Cryptosporidium parvum) and
- parasites such as helminths and their eggs (e.g. ascaris (roundworm), ancylostoma (hookworm), trichuris (whipworm))

I quoted this publication:
www.susana.org/en/resources/library/details/2636
Andersson, K., Rosemarin, A., Lamizana, B., Kvarnström, E., McConville, J., Seidu, R., Dickin, S. and Trimmer, C. (2016). Sanitation, Wastewater Management and Sustainability: from Waste Disposal to Resource Recovery. Nairobi and Stockholm: United Nations Environment Programme and Stockholm Environment Institute, ISBN: 978-92-807-3488-1

Are there other important wastewater publication that group helminth eggs not under pathogens?

You asked again about the survival time of helminth eggs. A couple of years ago I worked with a helminth expert from Mexico on the Wikipedia article on helminths and she recommended adding this sentence:

Helminth eggs remain viable for 1–2 months in crops and for many months in soil, fresh water and sewage, or even for several years in feces, fecal sludge (historically called night soil) and sewage sludge; a period that is much longer compared to other kinds of microorganisms.[12][13]
en.wikipedia.org/wiki/Helminths#Common_characteristics

I can't give you the answer about how many years (maybe a Google search would reveal it) but I think you get too hung up about absolute numbers regarding reuse. What I keep stressing about the WHO Reuse Guidelines from 2006 is that they broke away from the tradition of recommending absolute values and rather stress the multiple barrier approach. This means that if you have several barriers in place then the treatment step (for example) can be less rigorous than if you only had the treatment step as a barrier and nothing else. Personal protective equipment, education, the way the material is used - these are all additional barriers that can be effective.

you said:

I'd note that there doesn't appear to be a wikipedia article for wastewater reuses and restrictions.

Well we have this one on reclaimed water:
en.wikipedia.org/wiki/Reclaimed_water
(I did a lot of work on it during our edit-a-thon in March - it still needs lots more work though)

And we have this one on reuse of excreta, which I started some years ago (and which also needs more work):
en.wikipedia.org/wiki/Reuse_of_excreta

Regards,
Elisabeth

Hi Elisabeth, thanks for the links to the Gates Foundation grant database. So it appears BioFilCom got $ half a million, Bear Valley probably around the same, each with a focus on what you politely described as "other aspects". Given that these other aspects have certainly not been innovation around improved design for either reuse of wastewater or reuse of solids, perhaps by "other aspects" you allude to their business models.

For some reason I had assumed the Gates Foundation were focussing on supporting innovation and sustainable sanitation solutions, but from my perspective this has not been delivered in those vermifiltration projects. Good that Walter Gibson has made it clear that the tiger toilet was designed purely for user convenience, i.e. primary treatment to soakage field... no better than a septic tank.

With regards to such vermifilter toilets Kris was correct in saying

"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...a vermifilter's purpose isn't really pathogen removal."

However, I thought I had gone to great lengths to explain the difference between "vermifiltration" and "vermifilter toilet" in the wikipedia article. The problem as I see it is that the current crop of vermifilter toilet producers haven't actually taken advantage of the technology and are thinking no differently than Kris has described.

What I have repeatedly tried to explain in this forum is that vermifiltration can inexpensively produce treated wastewater to a quality suitable for surface irrigation of crops ...and even humus suitable for reuse directly as a soil conditioner in soils used for food crops - a truly sustainable solution by closing the nutrient cycle and breaking the helminth cycle. However, neither Walter Gibson's tiger toilet, nor the Biofilcom vermidigester toilets achieve this. On the other hand:

1. Staged vermifiltration offers pathogen and parasite removal and can render wastewater suitable for irrigating crops.
2. Dual digesters offer resting of humus to destroy parasites.

Both are simple low cost innovations that are not yet available to the sustainable sanitation community, because monopolies have been set up using grants for first-mover advantage rather than innovation. I'm only here to try and open-source the alternative to their prematurely delivered products: Domestic treatment plants that are easily built from readily available low cost materials.

Regarding buildup of humus, it is not hard to calculate volumes of fresh solid waste generated per user per year and divide by ten (Furlong et al.). The 20-40 kg of humus per person per year amounts to a volume that should not be ignored. It certainly should not be ignored if sustainability is the aim. It is an important component of the whole system because it amounts to the non-degradeable non-soluble organics in our waste. That "one tenth" is precious, humus that could contribute to the productivity of soils rather than be "just waste".

Next, it should be understood that the buildup in volume of solids is dependent not only on number of users, but also how well the (vermi) filter works. Wastewater requires some pretty serious filtration to remove all suspended solids, which anyone who has measured sedimentation of sludge out of wastewater would know can be of a significant volume.

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.

How often you need to remove the humus is actually a simple capacity issue. I don't believe it is possible to "minimise production of vermicompost", the current estimate is that one kilogram of shit produces 100 grams of humus. However, hearing self-praise regarding slow buildup of solids does suggest poor filtration. The consequences of this? The clock will be ticking on the inevitable failure of the soakaway, leading to groundwater pollution.

Helminth eggs are very fine and removal of these from wastewater requires a high level of filtration, or alternatively sedimentation. Of course these Gates grantee "vermifilter toilets" all use underground soakaways, so there is no need to concern ourselves with parasites or pathogens anyway... or reuse of nutrients and water, just the convenience of the users. An aspirational model from the developed world.

but helminth eggs are part of the pathogens

When discussing treatment of wastewater I differentiate between pathogens and parasites. I consider helminths parasites rather than pathogens and would appreciate discussion in this forum using those terms to avoid confusion. This is because pathogens and parasites need to be treated differently for re-use of waste streams. Helminths (parasites) are usually removed from wastewater by filtration or sedimentation because they resist destruction. Pathogens (e.g. fecal coliforms) are destroyed by other microorganisms in short order in an aerobic environment. Different time frames, different organisms, different processes (removal vs destruction). Then there are other organisms such as giardia (a "parasite"), but testing of wastewater is usually for helminths or fecal coliforms.

they (helminths) can survive in soils for years

How many years? Do I rotate my dual-chamber primary vermi-digester every three years or every five years for the humus to be free of helminths? Once I know the answer, I can then design for the capacity required to ensure my humus rests for the required period.

In nine years of using my own domestic system, I've removed the humus fraction from my digesters once. I rotate between two chambers and rest each side 5 years. How often you need to remove the humus is a simple capacity issue, which is (or should be) set by the life of helminth ova. Because Bear Valley have working prototypes in India, these should have been used for helminth decay trials rather than brand promotion. So who is going to do the testing now?

Humus is quite different to sludge.

Fecal humus

Sludge looks disgusting and smells disgusting. Its a bit like comparing peat with mud, can the lay person tell these apart? Yes, definitely. The problem I have with these single chamber vermifilter toilets (tiger toilets, biofil digesters etc) is that the humus does not give off any warnings of what it might contain. It looks good and it smells good and it thus has appeal as a soil amendment for adding to the vegetable garden, just like compost or what we describe as "vermicompost". The risk isn't in handling it or digging it out of the vermifilter. The risk is from ingesting the ova on raw vegetables where fecal material was added to the soil. That is how the cycle is completed and reinfection occurs.

What makes it worse are quotes from Walter Gibson describing fecal humus as "vermicompost", which trivialises the safety issues around fecal humus. The wikipedia article on vermicompost rightly states that vermicompost is made from "decomposing vegetable or food waste". Such "vermicompost" can be safely added to the vegetable garden. Fecal humus should not be called "vermicompost", even where the process (vermicomposting) is applied to sludge.

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

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?

Certainly not. Discussing reduction values is only relative to the initial value. Human feces have about 10 million fecal coliform bacteria per gram! Absolute values are what is important, they quantify how much there actually is in the treated water. This is an important distinction, because relative values like 99% reduction, although they might sound impressive, are meaningless when describing effluent quality (which is why we test it). What is meaningful are actual levels in the effluent and comparing these with the values allowed for treated wastewater. Does the resulting water quality meet the WHO guidelines for discharge to waterways, or irrigation of crops?

So how are absolute values determined? The most commonly used methods for estimating coliform content are the multiple-tube (MPN) and membrane filter (MF) methods. The MF method measures coliforms as "colony forming units" (cfu), is faster and easier than the multiple fermentation tube procedure and is not as reliable where samples also contain non-coliform bacteria or high turbidity, so is usually used for testing drinking water. Because the results from multiple-tube fermentation are only an estimate, they are reported as "most probable number" (MPN) of coliform per 100 ml. Although Furlong et al. published that the mean thermotolerant coliform removal was 2-log₁₀ (99 per cent), the actual coliform content of the treated wastewater was 2010 cfu/100 ml (down from 471,400).

The relevant number is 2010 cfu/100 ml, not "99% removal". This number determines what we can do with the treated effluent.

Now, the WHO guidelines set 1000 cfu/100mL as the maximum for fecal coliforms for irrigation of food crops. So the tiger toilet produces effluent only suitable for discharge underground (soakaways), no better than a septic tank. I'm fine with that, but a recent research paper published evidence that vermifiltration can remove pathogens from wastewater to levels suitable for use in crop irrigation ("It is possible to eliminate fecal coliforms to 2.0 Log₁₀ of Most Probable Number (MPN) per 100 mL−1"). Nice that something has been published in line with my own research.

So....for simplicity, how about the sentence reading: "Vermifiltration can reduce the fecal coliform count to below what the World Health Organisation sets in their guidelines for unrestricted irrigation, such as to food crops."

I'd note that there doesn't appear to be a wikipedia article for wastewater reuses and restrictions. In my view this is important, because treated wastewater is often discharged to waterways or to land. The WHO guidelines are very important in this respect.
cheers
Dean

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):

+++++++++++++

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

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

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?

?

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

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.

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.
..Steve

++++++++
Note by moderators: This post was made by a former user with the login name smecca who is no longer a member of this discussion forum.

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

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

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.