Discussion about pros and cons of vermicomposting digesters, including groundwater pollution aspects

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Discussion about pros and cons of vermicomposting digesters, including groundwater pollution aspects

Hi Elizabeth,
to answer some of your questions from 27 August (see in this thread here ), vermicomposting digesters work very simply. The effluent flushes from the toilet in through the top and adds to a "heap" sitting on filtration media. The liquid drains away through the media and is discharged to land. It is aerobic because the heap composts in an aerobic environment and the worms introduce air into the heap. They are very effective at reducing bulk and with sufficient worms present the heap grows only very slowly. Thus the system is aerobic and is a "digester".

Vermicomposting digesters are being used around the globe for municipal sewerage treatment and here in New Zealand have been commercialised for on site household sewage treatment for a number of years. These systems incorporate flush toilets and filtered effluent disposal to land.

Having experience with vermicomposting digesters I would suggest that the comments in the video that the system never needs to be desludged and that the sludge turns to sand are not factual. Solids do build up, albeit slowly, in the form of vermicast humus. Also, importantly, suspended solids will remain in the liquid outflow even if the filter media is very effective. The more effective the filter media is, the more likely it will clog over time or require maintenance. A filter media that lets more solids through will require lower maintenance. The biofil system uses porous concrete, whereas we use wire baskets, shade cloth and bark as the filtration media on which the pile sits. Small amounts of solids do make it through and although further filtration is an option for the liquid, maintenance and cost become an issue with secondary filtration.

The vermicomposting system deals with the solids very effectively and virtually without odour. The question in my mind is around the liquid effluent. This is still raw sewage being discharged, just with the solids mostly removed. Here in New Zealand local authorities are accepting that this may be discharged as primary treated blackwater, thus application to land via effluent trenches under the soil, just as with septic tanks. The question remains about longer term clogging of effluent lines from buildup of solids which only time will answer.

Although its difficult at this point to know what Biofil are doing because of the lack of information forthcoming, it appears that before mass deployment some simple design improvements may need to be made so that:

1. fresh fecal matter does not need to be handled when removing the humus (every couple of years);
2. flooding of the chamber cannot occur when inflow volume exceeds outflow capacity (i.e. soil infiltration);
3. filtration flow does not decrease from buildup of organic matter (i.e. maintenance); and
4. the nutrients and water are utilised for irrigating useful vegetation (the required cycle for environmental sustainability).

None of these issues are difficult to resolve, The question remains around what the most cost-effective methods are. The technology is low-tech and eminently suitable for application in third world countries seeking low cost solutions for hygienic effluent recycling.

Cheers!
Dean

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Re: The Biofil toilet technology for onsite sanitation in poor urban communities (Ghana, Senegal, Bangladesh)

Thanks, Dean, that makes it a bit clear. Even though it is not so obvious to me that your point # 4 can be easily resolved. This is because the effluent would be carrying pathogens if people using the toilet are sick.

What do you call shade cloth? What kind of material would that be?

Kind regards,

H-A

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M.Eng. Environmental Pollution Control
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Re: The Biofil toilet technology for onsite sanitation in poor urban communities (Ghana, Senegal, Bangladesh)

Hi H-A,

there are a range of fabrics available (windbreak and shadecloth), these are very cheap. They are either knitted or woven and made from polypropylene or HDPE into monofilament or tape yarn. Thus the hole size varies dramatically and thus so too does the filtration capability. For example:

From my experience, of greatest importance is to discharge the flush on top of the pile. The pile sits on a layer of coarse bark and this acts as a kind of filter, with the cloth underneath to catch finer solids that filter through the bark.

This system requires flush toilet input to dilute the urine which otherwise will be too strong for the worms to thrive. Tiger worms will thrive and proliferate with nothing more than blackwater (water, human waste and toilet paper) influent, provided the environment is conducive for their wellbeing (i.e. appropriate temperature, drainage, humidity and moisture). Low flush toilets work, I've used the Dometic Sealand,
Dometic Sealand
...but because these don't have a trap and water seal there is a risk of flying insects that are part of the fauna in the chamber flying out when you flush. Biofil's "patent pending" microflush valve does not appear to overcome this problem.

Although producing pathogen-free effluent is the silver bullet, I'm not sure if that is always necessary. Of course every pathogen is different and some only require skin contact to infect, whereas others need to be ingested. Therefore methods of handling the effluent and the choice of crop would need to take into account the pathogens present, secondary treatment method, their persistence after treatment, how long they last in the environment, climatic factors, and what the vectors might be. The requirement in New Zealand and Australia for surface application of treated effluent is a biological oxygen demand of less than 20 g/m3 and suspended solids of less than 30 g/m3. No mention of pathogens.

Of interest to me is how well vermicomposting deals with pathogens, especially helminths. The literature is interesting in that results are conflicting, but most studies indicate significant reductions in the solids. Given that this technology is simple, inexpensive and likely to be effective at reducing pathogens (i.e. "win win"), I'd suggest 3rd party research is required into domestic vermicomposting flush toilet systems to quantify:
  1. pathogen yields in the humus; and
  2. pathogen yields in the effluent for full flush systems.
That would resolve the question around pathogen yields and potentially encourage further innovation in secondary treatment leading to irrigation of crops.

cheers
Dean

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Re: The Biofil toilet technology for onsite sanitation in poor urban communities (Ghana, Senegal, Bangladesh)

Interesting! I tried an HDPE fabric in combination with a gravel drainage when I was GIZ advisor in Uganda, so something similar to the Biofill treatment, but the fabric didn't last. It was what is used in the typical white sacks. Perhaps the temperatures in the chambers were too high and was making the plastic brittle.

As for the control of pathogens, I'd go with urine diversion as explained earlier. In that case, most of the nutrients would be either in the urine derived fertilizer and thus free of pathogens after some little storage, or in the worm compost, thus also strongly reduced in pathogen counts after some months of storage. The effluents would be easily treated in a Canna bed or something like that.

Cheers, H-A

Hanns-Andre Pitot
M.Eng. Environmental Pollution Control
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Re: The Biofil toilet technology for onsite sanitation in poor urban communities (Ghana, Senegal, Bangladesh)

Those white sacks degrade in sunlight. Shadecloth/windbreak is uv stabilised and a much more durable material.

Constructed wetlands might remove helminth parasites and would be good to see helminth count at the other end of the canna bed comparing effluent from urine-diverting toilets with flush vermicomposting toilets. A simpler solution to achieve sanitary standards might be to drip irrigate nutrient rich raw effluent on high growing crops such as trees.

I understand that diverted urine would be free of helminths, but wouldn't treatment still be required to be free of other pathogens (lepto, typhoid etc)? Storage (time alone) surely wouldn't be enough for all urine-carried pathogens for use as fertiliser on crops? Also, wouldn't stored urine require aerobic treatment leading to loss of nutrient (volatilisation of N)?

Simplicity is what is so appealing about flush-vermicomposting. No problems with subsurface soakage fields feeding crops using raw filtered effluent (apart from cost of the fields or where the water table is too high), this is a much improved primary treatment system from traditional septic tanks. The technical challenge is to cost-effectvely get the liquid component from the full flush system suitable for surface application. Biofilcom are supposedly working on this, as are other funded bodies such as GSAP, LSHTM etc. Adane Molla seems to have uncovered opportunities with his research on secondary treatment of the liquid effluent (attached) with a significant reduction of helminthic parasites using filtration through red lateritic soil media, suggesting innovation holds the key, with the lowest cost and simplest method winning the day.

cheers
Dean

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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Great idea. your point could be taken up by the team then. i am also interested in working on something like this.

Bismark D-A
Dept. of Environmental Health and Sanitation.
College of Agriculture Education
University of Education, Winneba
Asante-Mampong, Ghana
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Dear Dean, HAP and all,

I follow with interest the discussion about the (BioFil) vermicomposting technique and always try to compare its pros and cons with other alternatives we have, i.e. UDDT, VIP, flush and septic/soakaway, …

60-70% of the population in our town Moshi/Tanzania (200,000 E) use pit latrines (traditional or VIP) for which no proper service chains (emptying, transport, treatment, disposal/reuse) exist. And the authorities pacify them with the hope that ‘one day’ they all will have flush toilets connected to sewer or septic tank. Wishful thinking for the majority of them in my view.

Is vermicomposting a possible alternative if they have enough flush water and can afford to use it to flush shit? Therefore the question: does vermicomposting works with pour flush (by bucket) or low flush systems? I understand for the survival of the worms, the urine needs to be diluted by flush water. Is 2-3L sufficient?

I fully agree with HAP that a good alternative would be a UD interface where the urine is separated, collected, treated and used separately. But that requires a second service chain only for the urine which is also the reason why I am a bit sceptical about UDDTs: if 30% of Moshi (60,000 E) use UDDTs, every day about 60m3 of urine have to be collected, transported, treated (stored!) and reused. It is valuable fertilizer, but can it be processed economically?

I have the idea to use the vermicomposting with a ‘pour flush cum double pit system’ (S-6 of EAWAG Compendium). The ‘filter’ (basket, cloth, bark) sits on top of an ordinary soak-away pit. Of course the area must be appropriate for pit latrines and soak-away by ground water level and geology. The standard pour flush toilets sends the faeces (and urine) to the filter. Once the filter is full/clogged, the pipe from the interface is re-connected to the second pit.

The filter of the first pit is emptied once the latest excreta have been vermicomposted and the pit can be reused once the second pit is full. The flush water is percolated into the underground as with any pit latrine or soak-away after a septic tank (subject to favourable ground water and geological conditions). With this system the effluent (raw sewage?!) will not be re-used, but also has not to be handled.

The system will resolve three problems raised by Dean: 1) no handling of fresh sludge on top of the filter, 2) no overflowing of the effluent chamber (subject to ground conditions) and 3) once filter cannot handle inflow anymore the inflow is redirected to the other pit.

If the question of economical processing of large quantities of urine can be resolved the system can be upgraded with a UD facility.

If the underground is not favourable for infiltration of sewage effluent, the pits could be constructed as impermeable tanks (cess pit) and can be emptied regularly (bi-monthly only for black water?) with a vacuum truck (honey sucker), but that will be expensive, then the use of UDDTs may become more economical.

Looking forward to your comments and ideas,
Ciao Hajo

Happy New Year to all of you !!!

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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Hi Hajo,

the key advantage with vermicomposting is that only the liquid effluent needs to be disposed of. With low flush "outhouse" toilets (I've found as low as 500 ml water per flush is enough dilution) the liquid effluent can be directed straight down into a simple soakaway so is simple and reliable. Not so good with piped effluent (indoor toilet) though, because enough water is needed to carry the solids. With full flush (indoor) toilets effluent fields are required because of the volume of liquids potentially contaminating the water table.

The double pit system would likely work if there was sufficient soakage. Insufficient soakage and the level rises and kills the worms. Remember, the pit will no longer fill with solids, so for longevity its all about soakage.

You can actually have one good pit (soakaway) with two baskets. I've attached a pic of what I do here in New Zealand, a twin basket system. Ideally the tiger worms can cross between baskets so a single chamber with twin baskets is best... but chambers would need to be constructed properly to be fly-proof etc and accessible for digging out compost.

There is no need to separate urine, so why do that? Follow the KISS principle...

Have a look at this video, it shows a simple low-flush toilet, vermicomposter and soakaway system (GSAP Microflush toilet).

Microflush toilet

I've attached an image that shows a full flush system for primary treatment. This includes a settling tank, which is not necessary for a simple low flush - soakaway system (I'm also into secondary treatment and irrigating with drippers).



(Also attached as a higher quality pdf)

cheers
Dean

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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Dear Hajo, dear Dean,

Thanks very much for your interesting contributions!

The use of urine as a fertilizer can work beautifully on your own plot if there is a) the land/cultures available, b) the time and interest, and c) some tolerance of the odors associated with the fertilizing activities. In that case, which may be applicable to a lot of small towns and villages in Africa, the cultures can even be used to recover some of the investments that have gone into the toilets.

In terms of storage, apparently you only need a couple of days in order to kill the urine born pathogens (bacteria), but what is recommended is a storage time of at least ten to fifteen days in order to reduce odor. That depends on the temperature, higher temperatures require less storage time.

Of course, not everybody is into the use of urine on his or her plot, so that in larger communities, some kind of collection system would be required. For that to be successful, there needs to be a local market for the urine fertilizer with people who are positive about that kind of fertilizer. In that case, you should be able to sell the fertilizer at a rate that is considerably lower than what artificial fertilizers cost (and these ones can only get more expensive in the longer run). In terms of storage time, what makes things a bit complicated is that you'd have to assume that some of the urine may be cross-contaminated with feces, which increases the required storage time to months, depending on the ambient temperature.

So, I think if the interest is there on the side of farmers urine separation and collection may be worth the trial. Especially since the alternative of having urine/effluents drain into the soil is not a long term alternative. Hajo, the currant situation in Moshi appears to be that close to 200 m3 of urine are going into the ground water every day - that basically makes it impossible to use that ground water for domestic uses apart from irrigation. In many parts of Africa, hand pumped bore holes are still used for water supply, so pit latrines, soak pits and the likes ought to be avoided.

For a town like Moshi, where I would presume there is a crowded center, at least for the crowded parts of town, and assuming the funds are available, the drainage of effluents via a small-bore (solids-free) sewer system with the aim of treating and using the effluents for irrigation would in my view also be a very nice option. In that case, all liquids (gray water, urine, pretreated black water) would all go into that sewage system, but care would have to be taken about commercial/industrial effluents. And for the biofill toilets, there wouldn't be an immediate need to divert the urine, apart from, possibly, protecting the worms from overdoses of ammonium and anaerobic conditions.

And concerning the textile we were using, Dean, that was inside the toilet, so there must have been another reason for it to get brittle than light. It could be elevated temperatures because we used black metal doors on the chambers in order to raise temperatures. It could also be the chemistry of the environment. Of course, higher temperatures are not what worms like, so we had plenty of other bugs, like black soldier flies. In that regard, and for the odors, the flaps that the biofill toilet design is including, would have been very helpful.

And Dean, unfortunately, the writing in your drawing is not readable, but the double chamber design is ok for larger toilets; that's what we also used. But, of course, it's also more expensive.

Cheers, H-A

Hanns-Andre Pitot
M.Eng. Environmental Pollution Control
presently in Seesen, Germany
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

The forum software is reducing the size of images to 35kb, so to get around that I have attached a pdf of the diagram with readable writing...
forum.susana.org/media/kunena/attachment...posting-digester.pdf
cheers
Dean

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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Dear Dean, H-A and all,

No question that the ground conditions must be appropriate for the soakage of whatever flush is used (low, pour or full flush). This condition should be established before any type of sanitation system based on infiltration is built whether vermicomposting, septic/soakaway or pit latrine.

Further, the groundwater level must be deep enough to allow for sufficient cleansing/filtration of the effluent before it reaches the ground water table. How much ‘deep enough’ should be? There is some indication in the paper ‘Subsurface infiltration presentation.PDF’ which Dean posted (above) which indicates that loamy, sandy or red laterite soils of 1.5m give already a quite good reduction of waste water quality indicators (BoD, CoD, TSS, helminths). Another source of information can be the paper ‘Safe siting of sanitation systems’ which is found on the SuSanA library ( www.susana.org/en/resources/library/details/2155 ).

Therefore: about 200m3 of urine go into the ‘ground’ in Moshi daily but not necessarily into the ground water as part of it (how much we don’t know yet as we have not yet evaluated GWL or geological maps) is sufficiently treated by the over-laying soils before the effluent reaches the GW (remember: all GW is originally surface water filtered/treated by the soils and its micro-organism).

And I also see more problem of effluent from on-site sanitation affecting shallow water wells (5 to 15m) which draw water from shallow subsurface aquifer than in boreholes (20-100m) which draw water from deep aquifers where the sanitation effluent will be treated already when meeting the GW. And: Moshi has a sewer system of about 45km in the city-centre, that is not so much of our concern, rather the peri-urban areas.

I like the idea with two filter baskets on one soakaway pit and will think about how to convert Dean’s principal sketch into a design drawing considering fly protection and emptying service.@Dean: your copyright permits me to use your idea for further design?

Another question: Dean talks of Tiger Worms as the processing agents. I will have to look into what other worms could be used which are eventually available in Africa/Tanzania. Any ideas from forum members?

I agree with Dean to keep the system KISS and would possibly in a first try recommend not to use UD but keeping in mind that the urine can be a relevant fertiliser source and not ruling it out for good. At the moment I see the problem of collecting and storing (maybe for months) huge amounts (x.000 m3) of fluid if UD is introduced at scale. As Hanns-Andre points out, UD makes much sense if the toilet/plot owner re-uses the urine on the plot. But in a peri-urban/high density environment with small plots it is not feasible and a collection service must be provided for urine if UD to be used.

And we have to keep in mind that not ‘one stone kills all birds’: vermicomposting is a solution where people can and can afford to use water for flushing, because only about 60% of the Moshi population have house/yard connections. How far you want to carry water to flush your toilet? Thus, service chains for pit latrines and UDDTs have to be considered as well as possible extensions of the sewer system: city-wide sanitation planning!

Ciao Hajo

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Everything should be made as simple as possible, but not simpler. :-)
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Hi Hajo,

What I like about the GSAP microflush is all the flush water is provided by handwashing, which is essential anyway for adequate sanitation.

I only copyrighted my drawing, and encourage design using the principles offered. One key to design is sufficient surface area of the basket floor. Each basket needs a surface area of approx. one square metre. What happens is the piles "spread" as the worms work on them, and this should not be constrained by having too little basket-width, otherwise aeration will not be sufficient inside the heap for rapid breakdown, even though the basket walls allow drainage. Reinforced concrete seems to be the material of choice for Biofil/GSAP constructions, keep in mind that the solids can weigh a fair bit and you want a cool enclosure in the tropics.

Tiger worms are good because they are "self-contained". I'd be interested to know whether black soldier flies complete their life cycle contained within the enclosure, or whether the adults need exit and entry. If they need an entry/exit point, then would other flies having access become a hygiene problem?

cheers
Dean

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