I would add that dilution is always better than concentration. The more soil volume the effluent has to filter through, the better. Constantly inundating a small volume or surface area of soil (e.g. latrines) is asking for trouble. Soil particles attract nutrients, but once saturated cannot do so any more. Also, anaerobic processes are much slower than aerobic processes, therefore anaerobic soil does not provide conditions conducive for breakdown of pathogens. Biological oxygen demand of the effluent is important, because if high the potential for effluent to cause anaerobic soil conditions is increased. The golden egg is secondary treatment because drippers can disperse nutrients etc over a wide area and BOD is reduced.

cheers
Dean

Dear Andrea,

thank you also for the plenty information. As I said to Dean, 'a lot to read and to digest'.

I like especially your statement 'Depending on the type of soil this compartiment is extremely efficient in cleaning up, due to the microorganisms that live there in myriads, but also due to the long time it takes water to pass through because unsaturated flow is slower than saturated flow. And the effluents you introduce are not something poisonous to the life in the soil, it's natural, so its capacity to deal with it (treat it) will be high.'

It seems that subject to various condition being fulfilled which we have named and discussed before, soils can be an efficient protection for the GW.

We are at the very beginning of our sanitation activities in Moshi and once we have more information (and questions) I will come back to you.

Ciao Hajo

Dear Hajo,

thanks for the clarifications, I think you already have quite a good understanding of the hydrogeological processes. My main advise is that you put a monitoring routine in place and check the wells/boreholes in the surrounding villages in regular frequencies.

I always find it helpful to see these things in pictures, but I don't have one ready to upload, so just search for "groundwater contamination plume" and you'll see a great variety of illustrations available in the www, a lot of them referring to oil spills, hydrocarbon plumes which behave a bit different from sewage plumes, but in any case: the spreading of pollution definitely depends on the volume as well (see the last criterium in the checklist). From a groundwater perspective the contamination only starts once the pollutants have passed the soil (also called the unsaturated zone in comparison to the groundwater which is the saturated zone, because the pores are filled with water to the saturation point) and entered the groundwater. Depending on the type of soil this compartiment is extremely efficient in cleaning up, due to the microorganisms that live there in myriads, but also due to the long time it takes water to pass through because unsaturated flow is slower than saturated flow. And the effluents you introduce are not something poisonous to the life in the soil, it's natural, so its capacity to deal with it (treat it) will be high. But it depends on the time the microbes have to eat the nurtrients and fecal bacteria (etc), the longer the better, that's why too much volume might reduce the treatment capacity of the soil.

The treatment properties of the soil would not change unless the conditions change. Say you infiltrate so much urine over time that the pH (the acidity of the groundwater) increases (or better: decreases, the lower the pH the more acid the solution is), than you can even bring other contaminants into solution that were formerly no problem (because they were fixed to the rocks), for example see the Kabul study here (www.susana.org/en/resources/library/details/1437).

Another study you might want to look at is from Yaounde: www.bgr.bund.de/EN/Themen/Wasser/Projekt...erun/kamerun_en.html (has also been posted in the forum previously).

So regarding the threat your sanitation option might pose on the surrounding villages, you'll need to check a) what direction your groundwater is flowing in, b) what is the status of the groundwater now in those villages which would be affected by the outflow of your toilets ("Background value") and c) how does the quality of the groundwater there change over time (monitoring).

Hope this has answered some of your questions?!

All the best,
Andrea

Dear Andrea,

thank you for your information and advice. I am quite aware that the information provided is not sufficient for you to make any statement how safe GW could be in Moshi. And I was not expecting such judgement.

What I want to know is the following. The factsheet of WG11 "How to keep your groundwater drinkable: Safer siting of sanitation systems" describes how sewage sources under certain geological (soil) and geographical (vertical and horizontal distances) can or may not affect GW.

In combination with the research findings by Adane Molla (attached by Dean in one of his postings), I derived that loamy, sandy and red laterite soils have such good filter and treatment properties that under specific soil conditions and distances, soils can protect GW from sewerage contamination. The German 50-day-travel rule may also be an indicator for such behaviour.

Besides the confirmation that sufficient distance of the right soil will protect the GW, I also want to hear from you whether research has shown that this 'treatment' property of the soil remains over time independent of sewage loads, no matter how much and long sewage effluents are infiltrated. Someone may think that this is not possible, but I recall oil spills (where oil tankers ran on ground) and many years later nature had handled the oil. Maybe similar developments have been found in soils which have been loaded with sewage effluents for long time?

Why I ask this? It is not a problem for Moshi town as the main water sources are springs (85%) and boreholes (15%) above and out of the urban settlement. And in the lower lying high density peri-urban areas water wells exist but need to be forbidden for potable water as seldom the 100m (or 30m rule as it is in Tanzania) can be maintained. My concern are the villages outside Moshi which draw GW out of boreholes which could be contaminated by the massive sewage infiltration by pit latrines (65% of Moshi population) and septic tanks (15%).

Is that possibly prevented by the soils if they are of the right geology? Of course we have to investigate the geology and the GW aquifers, of course we need then 'hydrogeological maps, geological maps, soil maps or even ideally a vulnerability maps of the groundwater' as you rightly pointed out.

I hope my questions have become a bit clearer,
ciao Hajo

hi Dean,

thanks so much for the plentiful information and the websites of the commerical composters: a lot for me to read and to digest. I will keep you ( and others) informed of further developments and findings in Moshi.

Just one remark on your statement re helminths: 'There are conflicting references in the literature regarding helminth levels and I can only assume that increased resting time will lower levels of pathogens.' As far as I know from the SuSanA discussions, resting time may reduce other pathogen levels BUT not helminth eggs. They survive 3 years concreted in! You only kill them by heat, thus thermo-composting may do it (like the Higgin's Hot Box), the LADEPA does it by infrared.

The question could be whether the tiger worms eat and digest (all?) the helminth eggs and in such way remove them?

looking forward to further collaboration,
ciao Hajo

Hi Hajo,

thanks for your excellent questions. Here in New Zealand most systems used where there is no reticulated sewerage are septic tanks (primary treatment) or aerated domestic wastewater treatment units (secondary treatment). Septic tanks are cheaper and only installed where soil conditions meet requirements for underground effluent trenches (good soil drainage and plenty of space).

With secondary treatment the only requirements to meet for putting liquid effluent through drippers are 5 day biological oxygen demand (BOD) of 20g/m3 and suspended solids (TSS) of 30 g/m3. For primary treatment there is no limit, but an engineer needs to design the soakage fields to rigorous standards. Nobody here uses low flush or cares about water use, domestic systems are designed to meet these needs. In developing countries where vermicomposting is apparently catching on, they are using low-flush outhouse toilets with direct soakaway. I'm interested in what research is guiding the design for each installation.

Vermicomposting digesters are accepted here as primary treatment, thus standard practice is to connect to underground effluent trenches just as with septic tanks. I've been working on the next step, which is to produce secondary treated effluent at low cost using aeration, which has been surprisingly easy because of the effluent properties. I only have prototype installations, but there is a commercial vermicomposting system available in NZ using reed beds for secondary treatment.

Nobody here has ever questioned sanitary handling of digested solids and seem to accept claims of goodness-for-purpose. There are conflicting references in the literature regarding helminth levels and I can only assume that increased resting time will lower levels of pathogens. Thus in my view the only safe option is the twin chamber design with a year of resting before removal.

There are no problems with discharging kitchen sink water into the digester. Worms are surprisingly resilient to such things as soap and fat, even some disinfectant. However, the bulk of the greywater should be diverted from going through the digester. Bath and washing machine water doesn't have enough solids to justify putting through the digester and might go straight to the effluent field or secondary treatment process.

The thing is, once getting into household wastewater, each design will vary according to soil conditions, effluent volume and quality... therefore method of application to soil, all made much easier if secondary treated.

Vermicomposters have not become standard in New Zealand's domestic sanitation market. The market is currently dominated by expensive secondary treatment systems, all using essentially the same principle. Vermicompost digesters can only claim primary treatment status and only compete with septic tanks, which have gone out of favour. The opportunity I'm pursuing is to lower the cost of secondary treatment, which currently uses multiple stages - starting with a septic tank (anaerobic), then sedimentation with sludge recirculation, then aeration then filtration, then pumping to pressure drippers ...and costing NZ $10,000 -$20,000.

Happy to PM you a couple of NZ suppliers of vermicomposting digester 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

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

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

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

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

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