dear all,

I received a very valuable link from Elisabeth (Thank you!) to Griffith University in Brisbane where Prof Rajiv Sinah did all his research into worms and vermitechnology which I want to share with you.

We find a list of 7 literature sources under the search of ' vermifiltration '
and further 29 literature sources when searching for ' vermicomposting '.

24 of the above source have been (co-) authored by Prof. Rajiv Sinah, 12 have different authors. I don't know who is going to read all the stuff, but we need to know

• major findings about removal (destruction and/or filtration) of contamination (pathogens and toxins);
• and how far these findings have been confirmed or questioned by other researchers.
• Possibly we can also find in these or related researches, information about the agricultural value of vermi-cast (humus) and irrigation water. At the moment I have no clue how this is measured. I am hoping for some enlightenment by you.

Do we have anybody on the forum, who has read (and understood ) research results on pathogen removal and agricultural value for products coming out of vermitechnology? Then, please, report the findings here together with the related sources!

If anybody has read already one or the other of above sources from the Griffith University, then please give here a short abstract if the source relates to our core topic 'sanitation of human excreta'. I noticed that not all sources are 'open source', maybe Elisabeth can help then.

Thanks and ciao
Hajo

dear all,

The revived and further discussion of removal of pathogens (and toxins) from human excreta and wastewater should be guided by the intention that through VT these waste streams will be converted to reusable products, i.e. humus and irrigation water – and not by chance or accident but on purpose.

The removal (by filtration or destruction) of contamination (pathogens, toxins) must be looked at from following aspects:

• To which extent need pathogens be removed for a certain purpose? Subsurface irrigation, sprinkler irrigation, fruit trees, root vegetable or salad require irrigation water with different permissible pathogen levels. The treatment can be adjusted to this requirement.
• Vermidigester and vermifilter can provide a certain degree of pathogen and toxin removal. This has been researched partially but needs to be confirmed by specific and concise studies providing reliable design criteria.
• Removal of contamination can be steered by multiple stages of vermifiltration of effluent.
• Where VT alone cannot provide the level of removal required, other treatment stages will have to be added to achieve the required output quality. This may apply for i.e. specific toxins and heavy metals in industrial contaminated wastewater or forhelminth eggs in human excreta.
• Do the worms destruct the contamination in their tissues, or do they like filters just remove the contamination from humus and irrigation water but becoming hazardous waste in themselves? 

We may have to read through the previous posts in this thread, so that we do not elaborate on the same matters again which eventually have been already concluded.

Ciao
Hajo

Hi Hajo,
I have found that peer review before publication is not always thorough enough to pick up every deficiency in research methods or design, so what appears on the surface to be relevant results are later discredited by researchers who question the results, then re-conduct the experiment with an improved experimental design (that eliminates any confounding factors). Science is an evolution and scientists rarely claim to "prove" something, but only demonstrate the likelihood of the opposite not being the case. Hope that makes sense... but from memory there was a publication claiming complete removal of ascaris from sludge by vermicomposting. This was later discredited by other publications showing that this was not the case. The source is always quoted so the reader can evaluate the claim for themselves.

So yes, I am proposing that current design should be for a larger volume than what future design might be, to be 100% confident of safety. Volume shouldn't come at a significantly higher cost anyway.

Also keep in mind that the primary treatment system (digester) could be either a septic tank or a vermifilter. Primary treatment is just to remove and decompose most of the solids. However, septic tanks make sludge and vermidigesters make fecal humus.

Next, you are correct:

You 'filter' the ascaris out by sedimentation, then pump them back into the digester where they eventually die off after 2 to 5 years resting time. But that is 'settling' or 'sedimentation' of ascaris. What is vermifiltration?

I combine sedimentation with a secondary recirculation vermifilter. This recirculation vermifilter is not for removing ascaris, but to remove biological oxygen demand (BOD) and pathogens from the wastewater by recirculating through a biologically active aerobic medium from the last sedimentation tank back to the first.

Here is a diagram of an aerobic recirculating secondary vermifilter (plus primary twin digester/vermifilter):

This secondary sedimentation system could comprise settling tanks that are anaerobic (requiring a larger capacity) or aerobic (by using a recirculating vermifilter).

And if worms do not remove the ascaris they will be in their casting and remain in the top-layer prevented by the middle layer to be washed out?

Yes, the secondary treatment system could be a gravity operated vermifilter with a high hydraulic retention time that filters out the ascaris and suspended solids and lowers BOD:

Is it correct that worms in the secondary filter are only fed by the dripping of effluent from the primary treatment? Nothing else?

Yes, that is correct. My understanding is that worms digest bacteria and other biologicals that are active in the wastewater. The reason why wastewater has a high biological oxygen demand is that it is rich in organic compounds that are food for bacteria. The bacteria respire (consume oxygen) to digest those organics, which then lowers the dissolved oxygen levels in the wastewater. Because the levels of organics in that wastewater are so high, oxygen needs to be continually added to satisfy the oxygen requirements of the aerobic bacteria actively digesting the organics. So the worms don't need solids such as feces for food, but "graze" the bacteria. The worms actively manage the population of bacteria living on the medium, much like cows grazing a pasture to ensure the grass doesn't go rank.

The vermifilter itself, being an aerobic medium with large surface area, replenishes the dissolved oxygen in the wastewater.

And if it is right, then the settling/sedimentation of ascaris as you practice it, seems to me easier to operate and maintain.

I have found this to be the case because maintaining a high hydraulic retention time (a fine filtration medium that removes more suspended solids) is harder in practice than having a low hydraulic retention time (coarse filtration medium) with recirculation and sedimentation. Imagine what would happen if your inflow was a greater volume than what can percolate through the vermifilter...

cheers
Dean

Hi Dean,

nice to meet you also on this thread.. ... and you understood my questions correctly, sorry for being possibly a bit vague...

I am a bit surprised to read that some 'research' proves that vermi-composting eliminates ascaris and others do not. I had - the obviously wrong perception - that 'research' has such high standards, that results could only be publicised once they have been proven beyond doubt - of current knowledge. And I would assume that with current technique it should be possible to prove under which conditions worms eliminate ascaris and when not.

But, OK, as long as researchers do not agree on their findings, we have to assume 'your rule of thumb' that anything between 2 and 5 years resting time kills them. Unfortunately it requires larger storage volume than if we knew that vermi-composting eliminates ascaris.

My second question, you answered partially. You 'filter' the ascaris out by sedimentation, then pump them back into the digester where they eventually die off after 2 to 5 years resting time. But that is 'settling' or 'sedimentation' of ascaris. What is vermifiltration?

I have read the article on vermifiltration in Wikipedia, but there 'vermifilter' and 'vermidigester' is used ex-changeably. I see the chapter 'Secondary Treatment' which probably relates to 'filtration' of primary effluent and which is build like a slow sand filter in a water supply: top layer does the cleaning, middle layer supports the top layer, bottom layer extracts the cleaned water. Is it correct that worms in the secondary filter are only fed by the dripping of effluent from the primary treatment? Nothing else? And if worms do not remove the ascaris they will be in their casting and remain in the top-layer prevented by the middle layer to be washed out? Is that my understanding of vermifiltration right, otherwise please correct.

And if it is right, then the settling/sedimentation of ascaris as you practice it, seems to me easier to operate and maintain.

PS: my plan to build a private vermidigester, I had to shelf as I may have to change house but eventually I get the opportunity to build vermidigester toilets as demonstrations under my current project in Lusaka. I will keep you informed and surely will come back with questions as we develop the design.

ciao
Hajo

Hi Hajo,

I'm not sure exactly what you are asking in your two questions, but I'll try and answer anyway:
1. The point I am making is that a conservatively long resting period provides assurance that ascaris is eliminated from the fecal humus. Two years might be okay, but until published research is available that gives us confidence in that time period, I'm suggesting that four or five years is reassuringly sufficient. The capacity of the twin digester determines rotation length - the larger it is the longer the available resting period.
2. Secondary treatment can be by vermifiltration, but other methods are also available that eliminate ascaris. Traditionally, settling ponds are used in municipal plants because ascaris settles. I use sedimentation tanks to remove ascaris and other suspended solids that might block my irrigation drippers. Every five years when I remove the solids from one side of the vermifilter I also pump the sediment back into the primary-treatment vermifilter (or "digester") for composting.

cheers
Dean

Hi Hajo, welcome to this thread!

I have seen research reports that claim elimination of ascaris using vermicomposting of sludge, while others report no reduction of ascaris. Vermifiltration, on the other hand, can eliminate ascaris from the liquid effluent, but not the solids. I'm convinced that time is the solution to ascaris. The longer the solids rest, the less surviving ascaris. Twin digesters offer that solution and it is nice and simple, which is good!
cheers
Dean

Hi Dean,

questions on the last two bullet points of your last post (of 17.06.17, above):

1. vermi-compost from human faeces can be considered safe for any type of agriculture when produced in a twin-chamber digester because the dieoff of Ascaris (parasite) in human humus is (hopefully) somewhere between "125 +/- 30 days in faeces and 625 +/- 150 days in soil" and not beyond?
2. How does "secondary treatment to remove helminth parasites for reuse - again vermifiltration" can look like so that also the effluent can be used in agriculture without restrictions?

While I agree with Elisabeth saying
"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."
I also agree with your
"If reuse in crops isn't important for sustainable sanitation and "sanitation" is only about getting rid of our waste using short cut 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."
Why are we 'visitors' from the first world warned not to eat fresh salad in an African restaurant (boil it, peel it, leave it)?

Our aim must be not only to change from open defecation to a toilet that they like but also that the products coming from those toilets is safe for the use it is put to anyway. Whether we like it or not, farmers will put on the crops whatever promises a better yield, so let us make the additives safe and let us eat salads without fear.

ciao Hajo

Dear Dean, dear Elisabeth,

when I read enclosed research report, I was quite excited about the prospects:
"Vermi-composting is a self-promoted, self-regulated, self-improving, self-driven, self-powered and self-enhanced, low
or no energy requiring zero-waste technology, easy to construct, operate and maintain. Earthworms have real potential
to both increase the rate of aerobic decomposition and composting of organic matter in the sewage sludge and also
to stabilize organic residues by removing harmful pathogens and heavy metals."

Does this article contribute something new to the discussion you have been leading? I am not so much a 'chemist' that I understand everything and I am interested to hear from you, whether this research found that also ascaris/helminths(?) are dealt with by these wonderful worms: "Earthworms have over 600 million years of experience as waste and environmental managers of bio-waste, including human waste."

ciao Hajo

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