What can we reliably say about pathogen removal with vermifilters?

  • muench
  • muench's Avatar
    Topic Author
  • Moderator of this Forum; Freelance consultant (former roles: program manager, lecturer, process engineer)
  • Posts: 2176
  • Karma: 46
  • Likes received: 632

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

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

Community manager and chief moderator of this forum via SEI project ( www.susana.org/en/resources/projects/details/127 )

Dr. Elisabeth von Muench
Independent consultant in Frankfurt, Germany
This email address is being protected from spambots. You need JavaScript enabled to view it. Twitter: @EvMuench
Sanitation Wikipedia project leader: en.wikipedia.org/wiki/Wikipedia:WikiProject_Sanitation
E-mail us to get involved: This email address is being protected from spambots. You need JavaScript enabled to view it.
You need to login to reply
  • goeco
  • goeco's Avatar
  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
  • Posts: 176
  • Karma: 7
  • Likes received: 89

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

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 ( http://www.susana.org/_resources/documents/default/2-1004-summary-of-whoguidelines-for-the-safe-use-of-wastewater-excreta-and-greywater-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" ( http://www.sciencedirect.com/science/article/pii/S2090506812000504 ) and "Cryptosporidium infection can be mediated via farm soil and vegetables" ( https://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

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
The following user(s) like this post: hajo
You need to login to reply
  • hajo
  • hajo's Avatar
  • GIZ Development Worker, now in Lusaka | Zambia
  • Posts: 159
  • Karma: 11
  • Likes received: 66

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

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

This attachment is hidden for guests.
Please log in or register to see it.

We can't solve problems by using the same kind of thinking we used when we created them.
Albert Einstein
Any intelligent fool can make things bigger and more complex... It takes a touch of a genius - and a lot of courage to move in the opposite direction.
E.F. Schumacher
Everything should be made as simple as possible, but not simpler. :-)
Albert Einstein

This message has an attachment file.
Please log in or register to see it.

You need to login to reply
  • hajo
  • hajo's Avatar
  • GIZ Development Worker, now in Lusaka | Zambia
  • Posts: 159
  • Karma: 11
  • Likes received: 66

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

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

We can't solve problems by using the same kind of thinking we used when we created them.
Albert Einstein
Any intelligent fool can make things bigger and more complex... It takes a touch of a genius - and a lot of courage to move in the opposite direction.
E.F. Schumacher
Everything should be made as simple as possible, but not simpler. :-)
Albert Einstein
The following user(s) like this post: goeco
You need to login to reply
  • goeco
  • goeco's Avatar
  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
  • Posts: 176
  • Karma: 7
  • Likes received: 89

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

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

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
You need to login to reply
  • goeco
  • goeco's Avatar
  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
  • Posts: 176
  • Karma: 7
  • Likes received: 89

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

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

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
You need to login to reply
  • hajo
  • hajo's Avatar
  • GIZ Development Worker, now in Lusaka | Zambia
  • Posts: 159
  • Karma: 11
  • Likes received: 66

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

Hi Dean,

nice to meet you also on this thread..:cheer: ... 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

We can't solve problems by using the same kind of thinking we used when we created them.
Albert Einstein
Any intelligent fool can make things bigger and more complex... It takes a touch of a genius - and a lot of courage to move in the opposite direction.
E.F. Schumacher
Everything should be made as simple as possible, but not simpler. :-)
Albert Einstein
You need to login to reply
  • goeco
  • goeco's Avatar
  • Self employed innovator with an interest in wastewater treatment systems and recycling of nutrients
  • Posts: 176
  • Karma: 7
  • Likes received: 89

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

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

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
Attachments:
You need to login to reply
Share this thread:
Recently active users. Who else has been active?
Time to create page: 1.211 seconds