Dry toilets are usually designed to reduce volume by dehydration. That's a physical process which has nothing to do with the biological process of composting. I think it is probably not something that is very likely to be applicable to Ireland, where the ambient temperatures are unlikely to lead to dehydration in an enclosed latrine.

You may be correct that additions of some bulking agents act as anti-bacterials, but this may also explain how some basic composting toilets are able to show pathogen destruction. Wood chips and sawdust, straw, miscanthus and other materials are routinely used in many forms of large industrial scale co-composting, so it is absolutely clear that it is possible to find carbon sources which do not have the drawbacks you describe.

I think it is much more likely that the wilderness toilets are not composting due to too much nitrogen and too little oxygen rather than some kind of inhibition from the bulking material.

Large amounts of carbon in an enclosed space will not compost either unless there is sufficient aeration - and it may not even then if there is insufficient mixing of the materials and the air.

Finally, "cold composting" is a phrase which is sometimes used but is of little relevance to sanitation. At best the edges of the material are subject to composting (if they happen to be in a better aerated spot) but the rest of the material experiences very little change. Given that pathogens are able to reinfect, this material cannot be considered to have been treated.

joeturner wrote: All of these points have been widely studied in the past:

Faeces has a C:N ratio of about 8:1. Toilet paper has a C:N ratio of between 250-350:1, whereas sawdust has a ratio of 190:1.

Given that a) additional N is being added in the urine and b) that you need about a ratio of 4 parts sawdust to 1 part faeces (dry weight) to get to the lowest workable ratio (approx C:N of 16:1), it is pretty clear that ordinary toilet paper use alone is not going to give the optimum C:N ratio. Most sources recommend C:N ratios of around 30:1.

(figures from "Composting toilets as a sustainable alternative to urban sanitation – A review" by Anand and Apul, dx.doi.org/10.1016/j.wasman.2013.10.006)

Bulk reduction and pathogen destruction can only be achieved with high temperatures, which in turn can only be achieved with the optimum C:N ratio, aeration and correct moisture levels. As shown by Geoff Hill's work, systems which do not address and control these factors do not compost, period. Volume reduction might be happening due to losses in leachate or other biological processes, but it isn't going to be due to aerobic composting. And other non-aerobic processes are by definition going to be sub-optimal and likely cause other problems such as odor issues.

But maybe you're not really looking for a composting solution here - it sounds like you want to collect and treat the leachate and take away any remaining solids for treatment elsewhere. Which may be entirely fair enough, but what you are describing is not a composting toilet.

Hi Joe,

I am not looking for a perfect compost.

The optimum C:N ratios that you are describing are by definition irrelevant for a dry toilet, the main reason being that Thermophile or "hot" composting has only ever occured in systems where this ratio has been carefully calculated and the materials mixed, turned and aerated- this is not an expectation one might have with a dry toilet where the additions are small and haphazard in pattern or consistency.I have seen many dry toilets and none had "hot" composted, but they all decomposed and reduced in volume. The addition of a bulking agent such as sawdust or peat is also often counter productive as sawdust is high in Tannins for hardwoods and Terpenoids in Softwood- both antibacterial.

I had seen toilet contents mixed with sawdust decompose very,very slowly indeed despite being well aerated and drained. I believe this is resonated with Geoff's study - they seem to put huge amounts of it into toilets before and during use, knowing the types of trees that grow in that corner of the planet, we are probably looking at coniferous softwood. my guess is that all you do in adding sawdust is pickle the feces for a rainy day.

Peat is highly acidic and prevents decomposition in that way.

If I were to use a bulking agent I would go for straw or hay as they will maintain aeration and rapidly decompose.

All of these points have been widely studied in the past:

Faeces has a C:N ratio of about 8:1. Toilet paper has a C:N ratio of between 250-350:1, whereas sawdust has a ratio of 190:1.

Given that a) additional N is being added in the urine and b) that you need about a ratio of 4 parts sawdust to 1 part faeces (dry weight) to get to the lowest workable ratio (approx C:N of 16:1), it is pretty clear that ordinary toilet paper use alone is not going to give the optimum C:N ratio. Most sources recommend C:N ratios of around 30:1.

(figures from "Composting toilets as a sustainable alternative to urban sanitation – A review" by Anand and Apul, dx.doi.org/10.1016/j.wasman.2013.10.006)

Bulk reduction and pathogen destruction can only be achieved with high temperatures, which in turn can only be achieved with the optimum C:N ratio, aeration and correct moisture levels. As shown by Geoff Hill's work, systems which do not address and control these factors do not compost, period. Volume reduction might be happening due to losses in leachate or other biological processes, but it isn't going to be due to aerobic composting. And other non-aerobic processes are by definition going to be sub-optimal and likely cause other problems such as odor issues.

But maybe you're not really looking for a composting solution here - it sounds like you want to collect and treat the leachate and take away any remaining solids for treatment elsewhere. Which may be entirely fair enough, but what you are describing is not a composting toilet.

Thanks everyone again!

1. Dean - do you have more information on Clivus units in NZ, what were the issue, what is done with leachate, what are the capacities(clivus models etc.)and whether or not they apply bulking materials.

2. I think I have mentioned that in the case of the wild atlantic way, a wet toilet is not an option, neither is a UDT(Aquatron) or UDDT as they are too close to coastal water and are located in high priority ground water protection areas. The point that Carl made about reducing maintenance by planning for capacity and hopefully very little opening and closing of the chambers resonates with me in this context. I disagree that the C:N balance has to be rectified by adding bulking agent as it has been shown that fecal matter and toilet paper is mainly Carbon anyway, so if you want reduction of volume by volatilisation and microbial respiration, don't add work to your plate.
The so called "composting" that takes place is not of the type that happens rapidly, at least initially, but is a slow, continuous one which excellerates and slows down in waves, depending on changing temperature, moisture content and C:N Ratio, none of these should or can be controlled.
I am aware that a Clivus toilet is started with a bulking bed of woodchip but none should be added thereafter. The leachate is the key here - the content of the sump needs to be regulated so that drainage remains clear and relative aerobic conditions with it.
If by keeping volumes reasonable, we can empty the partly decomposed material once a year, we are on level par with septic systems in terms of cost and health exposure of maintenance workers, Having met the legal requirements and prevented pollution of coastal water. If we can do even less maintenance - all the better.

Is this a reasonable approach and expectation? your comments

Haha, I love how many different (and apparently contradictory) views we have all contributed here.

goeco wrote:
I'm just not sure about the need for dry composting, urine diversion or waterless toilets, seems to me that design is still being based on old and failed paradigms. Forget about addition of carbon, sawdust, poor decomposition, ammonia, smells, unsanitary handling of waste containing pathogens... these are simply consequences of poor design.

cheers
Dean

Mixed urine and faeces cannot compost on its own because of the high levels of nitrogen, so you have to add some kind of carbon source (sawdust, straw or something else) to get the material to have a C:N ratio of below 30:1. This isn't about "poor design", that's just about the biological processes involved. If composting is happening, it can only be when high levels of nitrogen are being lost from the system.

And the moisture level is also important because too much water will produce anaerobic conditions in the material and will inhibit aerobic composting. So "wet composting" seems to be a contradiction in terms, unless you are suggesting you've had good results with some kind of anaerobic decomposition process.

I also think there is a bit of a contradiction in what you've said: namely that you suggest mixing the faeces, urine and washwater to (presumably) produce quite a wet slurry (what would you think the dry solids would be of that?) but then you're talking about needing good drainage. Surely if you have good drainage below a container of slurry then you've still got the liquid to deal with, which may now also contain pathogens washed out from the slurry...how are you suggesting to deal with that?


On the point about the worms, discussions on this forum have always been looking at Ascaris, I don't think anyone has talked about counting anything else. I don't think I've heard the suggestion that non-hazardous worms are to be used as indicators of the survival of faecal helminths.

Clivus multrum-type toilets were introduced by the Department of Conservation approximately 15 years ago in wilderness areas of New Zealand. They have been relatively successful and retained in these locations. They are simple and do produce compost. However they are not foolproof... too many people use them just for urinating, so they can get smelly.

Those evil helminths... they are so misunderstood! Please somebody correct me if I'm wrong, but isn't the humble threadworm (pinworm or Enterobius) what tends to be counted in the "compost" product and as Bogdan said earlier, is contagious from eggs that abound on just about any surface, thus isn't specifically of concern from feces? The nastier roundworms (hookworms and whipworms) are of concern from infected feces, but is using a count of threadworm eggs as an indicator for roundworms always appropriate, given that people in developed countries probably don't have high levels of fecal-infectious helminths?

Arno, you stated in your video "If water is added to the feces in the dry part of the toilet system (even a composting system) odour will develop". Thats what I thought ten years ago before being introduced to wet composting. In my experience only good drainage and ventilation are required for low odour, not how much or little water is added...

...My point being that people still need to wash their hands, even when using dry toilets and in remote locations. Used handwash water needs to go somewhere and is not pathogen-free. Being reused as flush water is a great option, especially where water is scarce or soakage is poor. Compost worms DO NOT require urine diversion, nor anything else, apart from a regular supply of excrement and toilet paper ....and wash water. The wash water is the key, this dilutes the urine sufficiently for a happy habitat. Good drainage and ventilation are the only requirements for a reliable wet-composting system that is user-friendly and cost-effectively produces compost using worms. Of course there is then the liquid to dispose of.

Rested vermicompost produced from feces is not something to be afraid of, provided it has been reduced to stable humus. Well... I'm not afraid of handling it anyway and published evidence to the contrary is sorely lacking.

Soakage trenches are a well-proven technology for simple low cost sanitary disposal of liquid effluent. I don't see a small water supply and a soakage field as excesses for public toilets in developed countries, even in remote parks.

Elisabeth mentions a simple septic tank system with low flush and soakaway. Simple is good, but at some point it would need to be de-sludged and the sludge dealt with. Low flush toilet + vermicompost digester + soakage field is a recipe for success.

I'm just not sure about the need for dry composting, urine diversion or waterless toilets, seems to me that design is still being based on old and failed paradigms. Forget about addition of carbon, sawdust, poor decomposition, ammonia, smells, unsanitary handling of waste containing pathogens... these are simply consequences of poor design.

cheers
Dean

Ronniedeb wrote: A reed bed differs from a constructed wetland in that it has no surface water and utilises the reed's large surface area and density to transpire water away from root zone. The end result is Oxygen and biomass - both very valuable to the human cycle.

Thanks Ron for bringing in this important subject too!
I disagree that constructed wetlands distinct feature is surface water since I am personally involved with designing and building subsurface CWs in Ukraine (only subsurface). Always thought that "reed beds" is actually British synonym to CWs or "planted filter" or whatever. But this doesn't matter.
What is really interesting is the mentioned ability of those systems to notably and predictably transpire water in windy condtions so that we can use that feature for eco-engineering. Could you suggest any reliable reference what can be the figures in liters per square meter of planted area in relations to average wind speed, plant speceies and probably monthly average temperature?

Thanks To All.

1. Evapotranspiration occurs anywhere where there is a gradient between the leaf stomata and the air surrounding it, when the wind blows - it removes the diffused moisture. try to dry a pair of wet swimming jocks on a string by the beach and compare to drying over stove at home...
A reed bed differs from a constructed wetland in that it has no surface water and utilises the reed's large surface area and density to transpire water away from root zone. The end result is Oxygen and biomass - both very valuable to the human cycle.

2. Geoff - I think Arno made a correct point that the thinking should be nitrification and mineralisation fuelled by organic matter. as i pointed out, our study used direct fertigation(fertiliser solute irrigation) to see if the technology can be implemented in conjunction with UDDTs due to its ease of handling and feed per need nature. I agree 100% that it is better to perioidically infuse the soil with both urine solute and carbon source and let mama nature do its thing. just don't forget the latter

3. Geoff - clivus toilets do not require a top - up of a bulking agent, rather, it uses the carbon sources of the fecal and paper matter. In fact, there is a high likelihood that conifer sawdust is applied in the North American parks,which contains a lot of Terpenoids and alkaloids which are probably antibiotic and therefor unsuitable really.

4. Carl - Thanks you for the link. what exactly is the difference between your Toilets and Clivus'?

Hi Ron, Arno and Elisabeth and others who I have not met),
This is my opinion based on some 50 years of experience of the subject. A smart toilet is not primarily attempting to make solid compost of the feces paper but to contain, shrink and isolate the pathogens for a long period ... typically 30- 40 years. There are several ways to finish the process at that time which often coincides with a renovation of the whole station. One very interesting way is to close up and send in the soldier flies. They will finish off the untreaded feces in a few weeks. The liquid, derived from urine is the easy part as long as we don't add much water. see www.smarttoilet.se Using a flush toilet makes everything more difficult and does not add much.

We have found that setting them up to demanding maintenance is often the killer of these systems. If we design them to be left alone they do much better because not only are systems failing from NO maintenance but also from the wrong kind of maintenance. So I believe our best chance is to simplify, focus on making them odor-free and easy to keep clean and attractive inside the toilet room

Just to give the perspective from another country with beautiful national parks and excellent public toilet facilities at those parks: Australia (where I currently live).

When I lived here back in the early 2000s, I found composting toilets at many places in national parks - and in my experience they were usually clean, non-smelly and totally fine. Now this year, I have also seen other systems (but I am yet to find out if there has been a general shift away from composting toilets or not).

The other day, I came across this public toilet which calls itself a Hybrid Toilet System in a national park near Maleny in Queensland (sorry, the photos from inside of the cubicle are a bit out of focus; it was relativaly dark and I only had my mobile phone camera):







The toilet had a micro-flush, about 300 mL. When I used it, I assumed it was still a composting toilet but now when I tried to find the manufacturer's website in Australia, and I think it is probably this one:

www.gough.com.au/hts/commercial/nonflush_description.asp

They have a micro-flush and the non-flush pedestal version but in both cases the excreta drops into a primary tank filled with water - a bit like a septic tank.

From their website (www.gough.com.au/hts/commercial/faqs.asp):

Primary Tank
The process begins when the waste drops down the dropper tube into the primary tank. Due to the very small volumes entering the primary tank the detention time in the system is as long as 83 days or longer dependent upon usage.

This extended period of detention allows for very effective breakdown of the solids and very efficient settling and clarification to occur. The remaining undigested solids settle out to the bottom of the unit to form the sludge layer. As use continues, the sludge volume will increase until it begins to impact on the detention time of the effluent.

Dependent upon usage, it will normally be years for this level to be reached. This volume requirement and sludge level is established and controlled through the use of a sludge gauge, which is supplied with the unit. The management of the sludge is discussed in more detail in subsequent paragraphs. As in a normal septic tank this sludge is acted on and broken down by anaerobic bacteria.

Parasites
Another benefit of the long detention time is the containment of parasites in the primary sludge. Parasitic eggs have a settling rate in a column of water and these settling rates have been established by studies conducted by the World Bank. The detention time in the primary tank is long enough to capture the majority of these parasites thus creating a very efficient barrier against re-infestation.

Anyway, just thought I would mention this to give another example of what is being used in national parks around the world (I have no idea whether this toilet system is good or not; would need to do a bit of research on it). I will try to track down someone in Australia who has a good overview of composting toilets in national parks here and who can tell us more about the current state of the art. Perhaps Dean can also tell us more about the situation in New Zealand's national parks?

Regards,
Elisabeth


P.S. And just to balance it out, here's a photo of said national park:

Ron
Regarding fertilizing crops with fermented urine, it is important to remember it is the soil bacterial matrix that makes up the system that is receiving the urine. Nitrification will occur in oxygenated conditions and this is what is happening in functional mineralization conditions. This renders the urine acceptable to most plants. So the urine should be applied beside the plant and not directly to the plant stem. And the soil needs to be conditioned with organic material (eg compost) prior to planting so that nitrification will work. The Chinese treat compost with effective microorganisms in order to promote nitrification (they often call it nitrogen fixation, a misonomer, but it means the nitrogen is not being lost as ammonia to the atmosphere).
The leachate from a functioning Clivus is mainly dissolved nitrate, odorless and dark in color from the soil humus organics. This leachate could go directly to a planted area with bushes, trees or reeds if greywater is being mixed with the leachate.

Check out the website of Carl Lindström from Clivus where you find more information: www.compostera.eu
(and we can also invite Carl to take part in this discussion; he's posted on the forum before, see his forum profile and past posts here: www.forum.susana.org/forum/profile/userid-242)

Regards

Can you provide a link to this study?

Many sedges and grasses are adept at assimilating ammonia-N. It's one thing to fertilize a crop and another to plant a field above a urine leach pipe. First tries to get urine N back into human cycle. Second tries to prevent urine N from getting in ground water. I'd like to see which plants you found able to pull ammonia or were ammonia tolerant.

Urine diverting toilets produce up to 10x less waste volumes than sawdust toilets at high use sites. Smaller storage. Cheaper construction. Only need 3-4' below floor rather than a 6-8' basement chamber.

Geoff Hill - TTS