UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

  • goeco
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Correct. Having a gooseneck means a water seal or water trap that creates a full barrier from what is below. It takes more water to flush what sits in the gooseneck away, although there have been some innovations in recent times, such as Niagara's stealth toilet and arumloo that still have the water seal but improve on the standard dual flush. Micro flush usually has a seal that is momentarily broken to deposit the contents below using a hinge, for example dometic/sealand toilets and the Sato Pan, which is probably what you're looking for as it is a micro-flush squatting pan.

You'd probably find enough air will pass through the drainage layer with your solar method. The pile itself does need some air flow above it, but this should be easy to achieve with a simple vent. Don't worry about getting air into or through the pile itself.

cheers
Dean

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
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  • hajo
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Hi Dean,

I really value your advice. Thanks for the hints to micro-flush squatting pans, but even more for the advice that the pile does not need air going through just passing over. It’s these small tipoffs which make life easier… :)

Does the drainage require air passing through, if yes, why? If not, I can spare that solar driven air current.

Ciao
Hajo

We can't solve problems by using the same kind of thinking we used when we created them.
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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.
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Everything should be made as simple as possible, but not simpler. :-)
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  • goeco
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Hi Hajo,

The fresh air in the drainage layer will permeate into the refuge layer. The refuge layer is most important to keep aerobic. Don't forget that respiration is taking place with multiple organisms breaking down the solids, consuming oxygen and releasing carbon dioxide. Wet composting is still an aerobic process, but from the outside in, whereas with ordinary composting the process works from the inside out. The worms need air, this is best provided from both above and below...

cheers
Dean

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
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  • hajo
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

… we are lucky it is sufficient to provide air from above and below as it would be (almost) impossible to do so from the sides… Ok, then we need two pipes for the drainage layer, in and out.

… small amendment: shall we better say ‘vermi-composting is still an aerobic process, but …’ or not ?!?

Thanks!
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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  • christoph
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Hi Hajo,
I did not write for quite some time, but you provoked me to do so. I refer to your post #18499. I think much of the arguments I will mention are already written down (which is part of the reason why I did not write any more) even here in this thread and in Susana library, but I would not like to see your arguments without a counter perspective..

The numbers of your arguments I mention in parenthesis (#).

I have always been in favor of large UDDT models WITH RECOLECTION service of feces.

I see as Pour Flush with recollection as a very good solution equivalent to UDDT with recollection. But I think if you compare to Pour Flush with UDDT you have to see some critical aspects (some mentioned in (12)). And the arguments have been exposed (some in the beginning of this thread I guess):

a) You need water in order to be able to flush
b) You need a water level of groundwater which is safe to infiltrate material with coliforms
c) You should not have wells near by
d) You need infiltration capacity

(7) Yes definitely you should infiltrate the urine in order to bring down costs of collection.
( 8 ) I don´t understand why you compare with a monthly collection service. I do agree with you that these concepts are too expensive. But so… why don´t you compare with a two chamber system as in eThekwini? Than your recollection cycle drops two every 6 month or every year. The calcs are published in SUSANA somewhere.
(9) If reuse is possible with selling – perfect. If not it is just a safe final disposal system.
(10) Danger of handling - With a 2 chamber system you don´t have that danger as your feces are always minimum 6 month old.
(11) We had a case (we reported here as well some years ago) where half of the population had pour flush and half UDDT. A draught after implementation showed clearly one VERY strong advantage of the UDDT. You don´t need water.
- vermi-composting does not eliminate ascaris eggs (we already had that discussion on the forum somewhere)

So
(14) I keep, especially for Lima and desertic cities, my very strong believe that UDDT is the only model which could be implanted very rapidly and very efectivley as a service model.

So again I would like to point to our video which shows users in the city. Demonstrates the viability of the economic aspects of a recollection model and shows the way forward.


Regards
Christoph Platzer
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  • Arndt
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Dear Hajo,
Thank you for your respond and commends. It seems that in Tanzania the situation is indeed different. Where does this huge number of pour flush toilets come from? Self-initiative or governmental programme? And how about water costs and availability of water? You have correctly noticed that our webpage is not updated – sorry for that. Here I have attached a set of photos with our latest efforts.


Dear Bowenarrow,

Thank you for sharing your experience from Australia. However, while in your country the economy maybe allows the luxury of flush, in Namibia it doesn't. Water is here an expensive commodity. In Otjiwarongo where bulk water supply is available one m3 of water costs 40,00 N$ (2.86 US$/m3). But at the same time 35% of the population depends on food supply due to the current drought. About 40% of our population suffers from malnutrition. Water is short. Therefore most of our people just can’t afford flushing their toilets with drinking water. Even desalination which has been started at the coast will not change this fact, since desalinated water will always be too expensive for the mass. Interesting, that you also manufacture UDS-Pedestals. How is your design?

Dear Christoph,
Thank you for sharing your experience with UDDT. Even so, that much content was maybe already discussed on this forum, it makes much sense to repeat since most of us can’t follow up constantly. Here in Namibia I have also to repeat again and again: The Otji Toilet is not a bucket system!
However, it seems that your system has many similarities to the Otji Toilet. But instead of using two chambers we use two 90 litre drums which are exchanged twice a year – the pedestal is not moved. Also our Urine-Diverting Toilet Bowl is somehow different from yours. Our design divides only about 80% of the incoming liquid but is more user-friendly. The other 20% filtrates or evaporates. In fact all liquid which strikes the inner wall of the pedestal is guided into a channel regardless whether users are sitting or standing. The bowl is made of concrete with a special finishing (two component concrete paint) that allows the urine to adhere to the wall and to drain into a small trough at the bottom of the bowl. Further, above the urine trough the bowl ends with a tear-off edge to avoid cross-contamination of the urine with faeces. In 2010 we have the bowl patented in South Africa but in 2014 Eco Solutions cc decided to declare the technology as open source. This was decided to encourage other potential producers to join our efforts in spreading this user-friendly UDS-Design. Here some photos:

Greetings,
Peter

Peter Arndt
www.otjitoilet.org
Otjiwarongo, Namibia

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  • hajo
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Dear Christoph,

I always have and will appreciate your professional input on the forum and I am grateful you jump into this discussion even if you feel, most had been said before. This may be the case but it is difficult to keep always track of contributions and arguments, they sometimes crop up under topics where you will not expect them.

This is why I opened this thread to weigh the pros and cons of different on-site sanitation options for peri-/urban areas in Africa. I guess Elisabeth (vM) will be happy that we are now away from the details of vermi-composting and back to UDDT… :) She felt we were getting too much into details of VC but I think you have to discuss details especially as long as it is a theoretical discussion. And Elisabeth may notice that a discussion about UDDT can get as detailed as about VC. Developing sustainable service chains is like making a design drawing of where you have to ensure everything fits together.

Before I comment on your comments, I want to state that I am also a fan of the UDDT system, only felt it is not appropriate for large application (let us assume 10,000 households) in peri-/urban areas where people cannot (no garden, no land) or don’t want to handle the UDDT outputs themselves. This discussion with you (and others) may help to develop a UDDT service chain for large scale application in our context. Now to your comments.

1 Need for water
Of course the UDDT system has the advantage that it does not require water for flushing. But a Pour Flush system may also be sustainable because of the following reasons:

a. We try to develop a low flush system (< 2L/flush) really reducing the water use to a minimum also to ensure the survival of the worms in the pit;
b. Water is needed anyway for hand washing and anal washing as a majority of Tanzanians are ‘washers’ not wipers;
c. With the UDDT we have to overcome two psychological ‘obstacles’: 1) Tanzanians see the UDDT too similar to pit or bucket toilet and feel they are deprived of development if they accept this and 2) they have resentments imagining the use of human excreta as manure; both arguments can be overcome with training and awareness creation but why try so if other arguments also speak for the pour flush (under specific conditions);
d. Different from Peru, Tanzanian towns do not really have a shortage of water resources. Rationing is mainly due to lack of management (pump maintenance, non-revenue water). In Moshi 77% of the households have already water borne sanitation (44% pour flush). The problem is the unsafe collection, treatment and disposal of the excreta which we could improve with double pits and eventually vermi-composting.

2 Low ground water table
Fully agreed that the effluent/leachate from a pour flush twin pit system (PFTP) should not affect the ground water. But that applies to all on-site systems, like for septic with soak-away and pit latrines.

And what about the infiltration of urine into the ground at large scale (remember 10,000 households)? I remember from small holder irrigation schemes in Zimbabwe that their use of fertiliser affected the ground water so much that we could not have drinking water sources ‘downstream’ of those irrigation schemes due to high nitrate content. Could large scale infiltration of urine have a similar effect? Has this been discussed on the forum?

3 Hand-dug shallow wells
If the ground water is low as discussed above, there can be no shallow wells.
Still people may dig wells to have a water source at least in the rainy season from surface-near ‘aquifers’. Since we talk of peri-/urban areas the settlement density is so high that it will be near to impossible to maintain the 30 or 50m distance between sanitation facility and well which is believed (!) to be a safeguard against ‘ground water’ contamination. In such case people must be instructed not to use such water as drinking water which actually should be already the case today with all these pit latrines around.

4 Infiltration capacity
Fully accepted, where soil conditions (clay or fissured rock) prohibit percolation of effluent into the ground, all such on-site system must be prohibited: no pit latrines, no twin pit systems, no septic tanks with soak-away or leach field! The only solutions allowed are sewers or UDDTs.

5 Infiltration of urine

As asked above (see 2), I wonder whether this can be done at large scale.
If not, collection costs may be prohibitive and eventually rule out the use of UDDT. This is actually my major argument (except the cultural objections by potential users) against the large scale application of UDDTs in peri-/urban areas.

6 Collection service
I had done some rough calculations and had the feeling that even a monthly collection of dry faeces could eventually carry a collection fee which people would be willing and able to pay.
But… hmmm…. Why not double vault and ½-annual collection… I did not think of it. For me a collection service was linked with a single vault UDDT and the collection and exchange of containers by the service provider.

If the urine can be percolated and the cultural objections/preferences by potential users can be overcome this may be eventually a sustainable solution. Although it will require a lot more of persuading than in a desert city like Lima where the shortage of water and the unnecessary waste as flush water is more obvious to the people.

7 Disposal and reuse
Agreed that the handling of (6 months) dried faeces from an UDDT is less unpleasant/dangerous than of a container from a single vault UDDT with partially fresh faeces.

But as far as I know even the dried faeces from an UDDT are not free of ascari eggs!?!

If not further processed and made ready for re-sale, how do you recommend to dispose dried UDDT faeces finally and safely?

What are possible/recommended processes to make dried UDDT faeces ready for sale and reuse? I saw in the video mentioned that one town utilities intends to vermi-compost the UDDT faeces.

8 Case study
What is a ‘draught after implementation’? I guess a kind of survey. Can you please send me a link to that previous reporting?

9 Economics
In the video I did not see where the economic viability of collection services has been demonstrated. I would like to believe it is sustainable. Can you provide me with figures and calculations which show the economic sustainability, even if they are not (yet) real figures but still planned figures.


I actually think that we should not focus only on one sanitation solution in the urban African context. Sewers are justified in certain areas (build up city centres), WC can be used where there is enough water and people have the money to pay for (cost-covering!!) water and sewer services, pour flush toilets (with septic or twin pit) may be used where people strive for the ‘comfort of the flush’ and have the necessary water available. UDDTs may be the solution for dry areas and where people do not want to waste water for flushing. Finally, for all solutions the necessary sustainable service chains have to be developed together with the technique which in my view is the major challenge.


I hope very much that you are not bored by repeating arguments you have said before and I look forward to a constructive further exchange.

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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  • hajo
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Dear Peter,

I was surprised myself when our sanitation survey revealed that 44% of households in Moshi have pour flush (and 33% full flush). As far as I know there has been no Government or donor programme to promote this. It is initiated by the peoples’ desire for the ‘comfort of the flush’.

We were also surprised to find that only 8% of the waterborne toilets are connected to the sewer system, while 33% have septic tank and soak-away and 34% have a ‘new’ technology: trying to save investment cost (for building a septic) and maintenance costs (emptying a septic) users have just omitted the septic and feed the sewage straight into the soak-away which we now call a ‘soak-pit’ as it functions like a latrine pit. Faeces are stored and eventually degraded in the pit while fluids (urine, black-water, grey-water) eventually percolate into the underground if conditions permit.

Of course the soak-pit fills up like a latrine pit and we have observed that users have already problems with the emptying as with a latrine pit. The contents is too often too dense to be pumped by a vacuum truck. Only the top layer of fresh sludge can be removed and this has to be done at frequent intervals because the soak-pit receives more sewage than a latrine pit.

Since the problem surfaces only now, we have no solution yet. One idea would be to transfer the system to a twin pit system, i.e build a new pit beside once the first is full, empty the first once the second is full and then use them as twin pit system alternatively. Because of this new finding we also opt for the pour flush twin pit system as one possible solution in Moshi.

Water availability is not so much a problem in Moshi except for the rationing because of pump failures and non-revenue water. Also the network is quite extensive and even those people who have no yard tap/house connection need to fetch water anyway for hand-washing and anal washing. Water is cheap compared to your prices: about 700 TSH/m3 which is about 0.30 USD/m3.

Regarding the Otji Toilet. I like the idea of using two drums, of which one is emptied only every 12 months. Can you please explain better how the empty and full drums in the pit are exchanged? Do you experience problems with anaerobic conditions in the drums as 20% of the urine seems to get into drums? Ok, the drums are perforated, where does the ‘effluent’ from the drums go? Your users are majority wipers, no washers? You have not faced problems with the infiltration of urine in possible clay soils? I like the idea with the pet bottles as fly traps.

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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  • christoph
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Dear Peter,
I have always liked the design of the “Otji”. I never had the possibility to see one installed. I think it is a very interesting solution.
Dear Hajo,
It is not that I am bored. It is that I sort of lost hope to change something be repeating here the same aspects again and again .. .but that would be another thread. I would love to repeat as many times as necessary if I thought …. This can change something. We are working on large scale solutions since 2007. Finalizing our PPP project in Peru we did a video – lots of effort .. until now 500 views … did we change something?
To answer your questions (I will not be able to answer everything (time)):
See this publication here from 2007…
http://www.susana.org/en/resources/library/details/961
it contains a lot of numbers. It has been made to compare a UDDT solution with a fully established sewer and treatment. Therefore very expensive but you can draw some numbers there.
In another publication (at Latinosan this year) we worked on comparing different solutions for large scale in Peru, see publication attached (in Spanish). I would like to draw your attention to slide 11 I put it here as well.



It shows the lifecycle costs of 5 different large scale solutions. (from left o right: VIP pit, UDDT double chamber, UDDT single vault, Septic tank, sewer)

the costs from the bottom to the top: yellow - ivestment, blue - cost for water, brown - collection service, red - education

Leaving out the pit – as not comparable in quality of use - the UDDT double chamber (eco sanitario doble camera) has by far the lowest life cycle costs. I would imagine a Pour flush in the same range.
If you need more detailed numbers I have to dug deep.

You are asking which post contains the discussion and the example from peru. it is here:
http://forum.susana.org/forum/categories/106-user-interface-technology-innovations/2776-are-pour-flush-toilets-a-good-idea-for-south-africa#2785
(the link does not go to the post directly I don´t know why) - the post is at #2785

The last sentence there answers your concern in (5).
"As we promote urine infiltration for UDDT (when no use intended) we are often critically asked, especially from donor organizations, about the contamination with nitrate... even seriously questioned if the urine infiltration is legal… They do not ask this in the case of pit latrines or septic tanks with infiltration… really often the relation between rational solution – normal practice – and UDDT seems to be dislocated."

It might be interesting to read a bit around in that thread. The discussion about nutrients influence by UDDT continues in #2809.

We always recommend a secondary treatment after collection.

Please feel free to ask for more information if you need.

regards
Christoph Platzer

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  • bowenarrow
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Afternoon Arndt.
Attached pics show the Ultimate model that is popular in areas where septic systems have proven to be unsuitable. All our designs are waterless. The urine is completely separated by the use of a bowl which has a spigot that joins a tube under the floor for collection or infiltration. Collection is popular in Australia, breaking urine down 15/1 has proved to be acceptable for soil renourishment.
Our aim is to encourage re-use of both urine and solids subject to local conditions.
We relocated our manufacturing to Vietnam which allows us to market at a price less than conventional ceramic pedestals whilst keeping a modern appearance.







Cheers Ross
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  • hajo
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Dear Christoph,

I can understand your frustration but you must recall that such fundamental changes take time. I read on Wikipedia that it took 20 years to make the Germans accept the use of safety belts when driving – and they were only accepted after penalties were introduced.

Centralised sewer systems with WWTP have become state-of-the-art technology over 150 years. ‘Older’ W&S engineers have hardly learned anything else, only younger ones may know about alternative sanitation technologies if they became interested in them. Politicians, public service administrators and the general public in Europe and North America have little knowledge of any (alternative) sanitation. And what we use, serves as example for decision makers (and population) in the developing countries. All these factors produce a high moment of inertia against change. That is why I have those citations under my posts, always reminding us of our immense task.

Thank you for the link to your publication of 2007 with the detailed calculations for a large scale UDDT service chain for 10,000 households. Since that is the number I had in mind when thinking about on-site sanitation chains in Moshi, do you have an EXCEL worksheet which contains all the calculation which you present in the publication and would you let me have a copy as template?

I do not know Spanish thus do not understand the presentation of 2016 which you attached but the bench dbl vault UDDTs with the entire colourful tiles look nice. I am surprised by the very high collection costs of the single vault UDDT. Do you have an EXCEL sheet of the cost calculations which stand behind that graph and would let me have it?

It seems also to me that alternative sanitation (incl. UDDT) is judged more critical about its environmental and (public) health impacts with regard to ground water pollution, nitrate build up, ascari eggs, pharmaceutical residue, etc. If for some of the ‘criteria’ alternative sanitation can prove better results than conventional sanitation (sewer, septic) it can serve as a selling point.

But at least we should know what comes out of our systems. You did not mention ascari eggs, do we know what happens with them in UDDTs? When you recommend secondary treatment, is it just a safety precaution or you know it is indispensable? What is recommendable large scale secondary treatment for UDDT dried faeces?

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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  • Arndt
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Re: UDDT versus Pour Flush (with vermi-composting) versus ???: which are sustainable sanitation technologies and systems for peri-urban areas in Africa?

Dear Hajo,

Thank you for your feedback. Wow - water in Namibia costs about 10 times more than in Tanzania! Nevertheless we meanwhile also get to know those makeshift full flush toilets feeding sewage straight into a soakaway. As this soakaways (for the reason of costs saving) are usually even too small designed they used to overflow quickly, creating beautiful playgrounds for the children of the neighbourhood. Still; our councillors promoting this system even so that our Municipality does not have a vacuum truck.

Technically I think a full flush toilet connected to a soakaway must be bearing the highest possible risk for ground water? This risk must be even higher than from pit-latrine or pour flush. As I understand (please correct me) that pathogens are mainly located in faeces while liquid serves for transportation – if available. The more liquid is available the more transportation is provided reaching deeper grounds. The less liquid is available the less risk for ground water contamination is given.
The Otji Toilet diverts 80% of the urine which is infiltrated into the ground. At the Otji Toilet is no water involved, apart from toilet cleaning; Namibians are wipers. The urine is acidly and does therefore not sustain significant amounts of pathogens. I am also not aware of a case where the little urine of one simple household Otji Toilet (5 – 10 persons) would have been enough to exceed the capacity of our soakaway; even so it is small designed (300 x 300 x 500mm deep). The input from individual household members is in fact minim. And that doesn’t change with increased number of units, as each unit have its own soakaway. However, we have to admit that the soil at this particular spot where the infiltration takes place is finally somehow over fertilized (max 1m3). But the risk of ground water contamination is still minim.

Problems with insufficient capacity of a soakaway for urine we have got with Toilets where bars are attached to. In some cases bars in our peri urban area having 200 customers almost every night, all these people using one or sometimes two Otji Toilets. Therefore for bars as well as for schools we recommend the installation of external urinals. There we use conventional urinals, but do not connect them to water. Those public facilities anyway must get cleaned and flushed manually once a day from a cleaner. That is enough to avoid production of ammonia out of urine since this would take two days. Also our soakaway for public facilities is of a bigger design. But even faeces are used to be more at those bars. At some bars we must change the drums on a monthly base, since the whole neighbourhood is using them due to lack of own toilets. However, in these cases the faeces did not have enough time to dry nor to compost. So we have to remove relatively fresh faeces. To avoid visibility of fresh faeces and to reduce odour we then cover the drums with a lid before further transportation. However, we are proud that an Otji Toilet can manage to serve daily 200 people over many years without failing in function also we do not promote public toilets.

Attached are three photos showing how we remove the drums.
1. A safety bolt must be removed with a spanner before the lid can be opened.
2. With two custom-made steel hooks we lift out the full drum which was resting under the hot lid. Weight depends on filling level and moisture level. However, two people can always manage. A team of four services about 40 Otji Toilets per day.
3. From there the drum comes on a pick-up for transportation towards the deposit. An empty drum replaces it inside the chamber, but rotated with the other full drum which was up to now under the pedestal. At the deposit bulldozers push huge quantities of faeces on mountains, leaving them resting for years. After three years (please correct me) no pathogens should remain.

A challenging aspect is the input of foreign objects i.e. household rubbish. On average about 20% of the drums content is plastic bags (used for wiping), bottles (plastic and glass), nappies but even shoes and t-shirts can be found. However, as simple as the Otji Toilet is, this doesn’t harm the functionality. But it difficult the potential later use of degraded faeces.

About your question of the remaining 20% of urine. This indeed falls into the drum together with the faeces. From there about half (10%) is evaporating due to ongoing ventilation. We use a 220mm vent pipe (rolled from 0,5mm galvanized metal sheet) which creates much more heat than the usual 110mm PVC pipe. The remaining 10% urine does indeed filtrates into the ground within the chamber. To facilitate filtration we have placed the drums on a perforated concrete plate 10cm above the ground. This liquid should be considered as problematic, as it has gone in contact with faeces and could therefore contain pathogens. However, the limited quantity can’t provide significant transportation to bring those pathogens far away from the toilet. For an individual Otji Toilet we can assume less than 1 litre/day infiltration of urine which has got in contact with faeces (given 5 users x 1,5 litre = 7.5 litre; 10% = 0.75 litre). When we compare this with Pit-latrines we have 10 times more problematic liquid released multiplying the radius of potential contamination. Pour flush connected to a soakaway provides maybe 50 times more liquid. However, a full flush toilet connected to a soakaway, releases about 200 times more problematic liquid then an Otji Toilet.

Recently we discovered an interesting side effect of collecting faeces in removable drums. Even so, that Namibia is a dry country, we have experienced several times flooding in the last years. If an Otji Toilet stands in an area which is about to be flooded, both drums can be removed before the water enters the chamber. Once the water is gone and the chamber has dried up the drums can be put in again and the toilets is ready for use. With Otji Toilets the risk of water contamination during flooding can be managed.

Greetings,
Peter

Peter Arndt
www.otjitoilet.org
Otjiwarongo, Namibia
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