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

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

Hajo,

I don't think you can compare surface water (I suspect you are including rain water) with the discharge of unlined latrines or soak pits meters under the ground when it comes to ground water recharge - these are two completely different situations. What would be comparable to rainfall is irrigation - both are going through the complete strata of the soil. And concerning surface water like rivers, there also are natural cleaning mechanisms. Leach fields would also be somehow comparable if the piping is located just slightly under the surface. Unlined latrines and soak pits, however, are short cutting the upper strata, the top soil, in particular, which are the primary cleaning agents and where the naturally occurring microorganisms are located.

On the other hand, depending on the type of soil, mineral soil does have filtering and some iron exchange capacity, so that I wouldn't be too worried about small family toilets if they are located at a distance of boreholes (or wells). In Uganda, we used a ball park figure of 100 meters for the minimum distance from production boreholes, a figure which is certainly including a safety margin. But for larger toilets, like school toilets or communal toilets, I would certainly be worried. In my view, these should be lined so that they would require an emptying service, or alternatively discharge via a pretty large leach field, use wetland treatment or something like that.

Otherwise, success with your endeavors,

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)

PS: And I would agree with Dean, I think it is one of the strong points of that microflush toilet that it uses very little water, and 'reuses' water from hand washing. But wouldn't these small quantities of water, probalby usually less than half a liter per use, be affecting the worms?

Hanns-Andre Pitot
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  • hajo
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Dear Dean and all,

It is a good idea to use the handwashing water for toilet flushing. But for Tanzania we will have to redesign the micro-flush system as Tanzanians prefer squatting pans. But it should be still possible. And I would prefer a system with goose neck, not only for fly and odour control but more for prevention of using the toilet as solid waste dump as it is the case with pit latrines.

Thanks for the hint with the required surface area to give enough room for the Tiger Worms to roam around for aeration and breakdown. On a 1sqm area what build-up of the heap would you allow for, spacewise and weightwise?

You mention ‘cool enclosure’. Remember that Africa may be a bit hotter than New Zealand and we cannot guarantee that not most of the filters/soakpits will be exposed to direct sun shine for most of a day and will become quite hot inside. Are the Tiger worms sensitive to heat? And are they sensitive to hand-washing soap?

Ciao Hajo

We can't solve problems by using the same kind of thinking we used when we created them.
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Everything should be made as simple as possible, but not simpler. :-)
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  • hajo
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Dear H-A,

I am quite aware that sanitation effluent and rain water are of different quality. And I also agree that the topsoil may have the highest cleaning power due to the micro-organism.

But the research by Adane Molla (see the paper posted by Dean, 04.01.16) seems to indicate that only 1.5m of plain loamy, sandy or red laterite soils reduces the contamination of the effluent by min. 50%. Thus for me it is a question of soil distance between bottom of pit/soak-away and GWL that the effluent is effectively treated not to contaminate the GW.

Also the other paper quoted by me (Safe siting of sanitation systems) does not emphasise that sanitation effluent must pass through top soil for proper treatment. It rather builds on type of soil (sand, gravel, fractured rock, karst), on GW flow direction, on aquifer depths, on sub-soil layering and protection (impermeable top layer), etc.

Because of the complexity of influencing factors these ‘rule of thumbs’ exist which give a rough guide how far the well/borehole should be from a toilet, because also the horizontal flow of the sanitation effluent through subsoil constitute treatment as stated by this paper.

Therefore I find your judgement too cautious. It is the first time I hear that a school or communal toilet should generally have a leak-proof pit (cess-pit) and should be emptied by vacuum truck. Which does mean there may be cases where it is necessary, but not generally.

I would be interested whether forum users (kanalwolf?) have information about cleaning abilities of subsoil and whether more research has been done in that direction beyond what Adane Molla has reported. I believe subsoil will also treat sanitation effluent, it is only the question what distance/volume of soil is required to remove all contamination.

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

PS

I just dug out a very interesting (old) posting:

'Last questions re Update of Factsheet 11'; 20 Dec 2011 00:16 #767; by Ian Pearson
from which I quote the following paragraph:

"travel of contaminated groundwater = only 5m : tests were undertaken in South Africa where VIP latrines were installed in sandy soil - an area of very fine sand. Test pits were dug next to the pit and samples of the shallow groundwater taken and analysed. It was found that there were no coliform bacteria at a distance of 5m from the base of the pit. Of course there were higher nitrate levels, but the fine sand had effectively filtered out the bacteria and larger microorganisms. We are well aware though that in conditions of fractured rock travel of microorganisms can be extensive."

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

It seems that some water in the flush is necessary to keep the heap from dehydrating, thus avoiding concentrations of urea building up. My own experience is with a Sealand 500 ml flush, which wasn't soapy water... but the GSAP microflush has proven successful using a minimal flush of soapy water. I also assume that in tropical countries some measures to mitigate buildup of heat would be wise. Such things as white paint and good ventilation... even some shade if possible.

I've found 600 mm height from the top of the bark to the inlet (or bottom of open microflush hinge) is sufficient, but that is for a family household. Generally increasing the width will achieve better breakdown with higher solids input than increasing height.

cheers
Dean

Dean Satchell, M For. Sc.
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Hi Dean, dear all,

Thanks for further info. I just found that the WikiPedia on vermicompost is quite informative: en.wikipedia.org/wiki/Vermicompost .

It contains the following info on temperature:
The most common worms used in composting systems, redworms (Eisenia foetida, Eisenia andrei, and Lumbricus rubellus) feed most rapidly at temperatures of 15–25 °C (59-77 °F). They can survive at 10 °C (50 °F). Temperatures above 30 °C (86 °F) may harm them.[13] This temperature range means that indoor vermicomposting with redworms is possible in all but tropical climates.[14] (Other worms like Perionyx excavatus are suitable for warmer climates.[15]) If a worm bin is kept outside, it should be placed in a sheltered position away from direct sunlight and insulated against frost in winter.”

Further I just ordered the following book on vermicomposting which has been used in the WikiPedia article as source extensively:
Worms Eat My Garbage, Paperback – 6 Oct 2003, by Mary Appelhof, ISBN-10: 0977804518

Dean, we have been talking of how small quantity of water is sufficient and whether soapy water is permissible. I have just been thinking of converting an existing septic tank / soak-away system into vermicomposting/soak-away by converting the septic into a vermicomposting device. That would mean that plenty of water including greywater from kitchen and bath would pass the vermicompost. Any experience with this on your side? Should be as you say in your first posting: '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...'

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

Hi Hajo,

A septic tank may not be ideal for setting up as a vermicompost digester, not sure how you'd ensure the water level always remains below the basket, given the outflow is at the level of the effluent field. If you have an existing septic tank and soakage field, it might be best to put a digester before the septic tank. The digester needs to be above the level of the septic tank, but below the level of your toilet. Having the digester there would mean the septic never needs to be cleaned out (normally done every few years) and the effluent quality would be improved. Kitchen sink water and toilet waste go through the digester then into the septic, while other greywater goes straight into the septic.

cheers
Dean

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

Dear Hajo and all,

you kindly asked me to give professional input regarding the groundwater protection from pathogens with regard to the Biofil toilet. Thanks for bringing groundwater into the discussion.

I read through the discussion thread but didn't find much background information on the main parameters we'd need to consider, i.e. how deep are your pits (I guess they are not lined?), what is the geology like in the area you are setting up the toilets in, how deep is the groundwater level (mind the different seasons, the water table fluctuates), how far are the wells/water supply boreholes and how deep are they? How is soil into which the pits are dug, is it mainly sand or even coarser material or loamy with clay...?

Please also have a look at the working group 11 product "How to keep your groundwater drinkable: Safer siting of sanitation systems" ( www.susana.org/en/resources/library/details/2155 ).

You also need to check from where the urban communities get their drinking water, is it from the local groundwater into which the toilets might pollute or are they being "serviced" from further outside town?

Maybe the ministry that governs water resources has maps that can help you find the information (hydrogeological map, geological map, soil map or even ideally a vulnerability map of the groundwater).

Best regards,
Andrea
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  • HAPitot
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Re: Questions Experts Ask vs Questions PRISTO Customers Ask (about Biofil Toilet Systems)

Dear all,

Thanks, Andrea, for this clarification. Just a small addition from my side: That result from SA you were citing, Hajo, can be interpreted in many ways. Of course, nitrate is a regulated contaminant in its own right, although not particularly serious. When I was working in Moroto, Uganda, we actually tested boreholes for nitrate as an indicator variable for fecal contamination, mainly because of the ease of implementing such tests. In addition, even though Coliform bacteria or E. coli are standard as indicator organisms for fecal contamination, enteric viruses, in particular, are known to travel further, so that a Coliform test isn't conclusive.

Moroto, Uganda, sitting on the lower slopes of an extinct volcano, must have a geology which is a bit similar to the one of Moshi, even though the town is very much smaller (with 25000 inhabitants), so you may be interested in some details from that town. Of course, there was no sewage system, and about half of the people had no toilet. The underground is characterized by a lot of boulders and stones, with loam filling up the gaps and a clayish soil on top, and with a lot of local variations, layers of clay or gravel, etc. All the former production boreholes in town had been given up, either because they didn't yield much or because of contamination. For example, there was one borehole that was at one time equipped with a solar, and when they started using it, it turned out to be contaminated and had to be given up. Now that water is considered 'soup', and that area is characterized by a lot of small houses, each one having its pit latrine in the backyard.

In Moroto, there also are a lot of hand pumped boreholes, one third of the public ones were found to be contaminated either because of E. coli or high levels of nitrite, or both. The precise reason for the contaminations is unclear, it could either be because of toilets or because the boreholes are not properly sealed, so that surface water or groundwater from contaminated upper layers is trickling down along the borehole. Of course, nobody is guaranteeing the quality of the water from these boreholes, but there is also nobody who is closing them down since a lot of people are relying on them.

The new production boreholes are now located above town towards the mountain, but the town is now already creeping into that area, and the challenge is to make sure people do not use toilets that are polluting the ground water - ideally using that 100 m rule - and I don't envy the people currently responsible for that task!

So much about Moroto, hope you've found something useful for Moshi! And I think you can now understand the central government, the owner of these water supply installations, who has come up with that 100 m rule.

I think, first of all, it is a matter of principle to contaminate the groundwater as little as possible and to support local farmers if the interest and demand are there.

And Peter, thanks for the pics! I like the vertical gardens. Are they ever going to be harvested?

Cheers, H-A

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

Dealing with the liquid effluent from a vermicompost digester (please everyone, Biofil is only a brand, not the process) is an important issue because of the potential for discharge into groundwater, just as with septic tanks and pit latrines.

Construction methods for the digester are important only in terms of cost. Biofilcom are apparently not disclosing anything about their design (manufactured), nor is GSAP (built on site), both recipients of substantial Bill and Melinda Gates Foundation grants. The Tiger Toilet brand, also a recipient of substantial grant funding, appears to have quietly disappeared, and I'd guess will probably reappear shortly as a commercial venture using the undisclosed research results for first mover advantage. Why am I so cynical? The thing is, the process isn't proprietary or novel, just the construction methods and design. Vermicomposting digesters have been around for some time and the process is incredibly simple - the only "novel" feature of the Biofil toilet appears to be using porous concrete as the filter.

Because the process is essentially the same irrespective of brand, different designs of digester would each produce similar quality effluent. Yet importantly from a sanitation perspective, nothing has been published by these grantees at all. Nothing on pathogen levels in the digested solids that might guide recommendations on the required resting time... Nothing on effluent quality and therefore nothing to guide recommendations for discharge into soil under a given range of environmental conditions. Nothing on secondary treatment using standard-practice domestic-scale processes such as reed beds or aeration/filtration. I'm sure the work would have been done though, because now the effort is going into market development.

Secondary treatment justifies the use of water as the carrier because secondary treated effluent is satisfactory for irrigating crops. The key advantage with the vermicompost filtration process is a significant improvement in biological oxygen demand for the primary treated effluent over that produced from septic tanks. The solids are separated and aerobically treated at low cost, then easily removed. This opens the the door for low-tech and inexpensive secondary treatment for all household wastewater, not just waste from toilets. Commercial opportunities abound.

Measuring levels of key pathogens, suspended solids and biological oxygen demand for the vermicomposting process (and any secondary processes being trialled) is straight forward and low cost research. Unless transparent, open access research reports are produced documenting the value of the process itself, the surreptitious situation of grantees engaging in non-disclosure of results followed by multi-level marketing campaigns to develop a brand monopoly will continue unfettered. Communities and households should be the beneficiaries - there needs to be open access to knowledge that provides the means to construct a digester.


cheers
Dean

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

Hi Dean,

referring to your earlier response to converting a septic tank into a vermicomposter: I am aware about the need to keep the composter levelwise between the toilet outflow and the inlet of the soak-away in order not to flood the composter. My question was not about this.

I want to know what experience you have with regard to grey-water (kitchen, bath, laundry) going through the vermicomposter. I am asking because on one hand you emphasise that '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 me that includes grey-water going through the composter. Maybe under condition to use less agressive/more eco-friendly cleansing agents.

On the other hand you state in your posting that 'Kitchen sink water and toilet waste go through the digester then into the septic, while other greywater goes straight into the septic.'

The question is whether tiger worms can withstand greywater loaded with soap and other ingredients which come with kitchen and bathroom waste water?

So far we also have not discussed about the hygienic/pathogen level of the solid waste produced by the tiger worms. I anticipated that it is known if the system has been commericalised in New Zealand. So I wonder why you ask in your last posting: 'Nothing on pathogen levels in the digested solids that might guide recommendations on the required resting time... Nothing on effluent quality and therefore nothing to guide recommendations for discharge into soil under a given range of environmental conditions.'

Can you provide us with references, websites, regulations, etc which indicate how far vermicomposters have become standard in New Zealand's sanitation market. That surely could help us to convince our local partners in Moshi of the viability of the system?

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
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