How aerobic are composting toilets really? How much pathogen kill? Clivus Multrum? And comparison with UDDTs

  • arno
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How aerobic are composting toilets really? How much pathogen kill? Clivus Multrum? And comparison with UDDTs

Note by moderator: The first few posts of this thread were originally in this thread about odorous gases from composting toilets.

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Last week I did a testimony for the Vermont Legislature on comparing composting and UDDT toilets. The term composting toilets is essentially a misnomer. These were the early ecosan toilets placed in homes. They mixed urine and faeces, produced odours and were not composting (properly). The odours were generated mainly from urine breaking down when in contact with faeces. Often these toilets would become overloaded with urine and leak. They have pretty well phased themselves out of the market but are still found. The chemistry of the odours is complex. The best research is on animal manure thus far. Take a look at this site on pig manure. www.thepigsite.com/articles/4234/underst...chemistry-of-odours/

A true composting toilet is the Clivus multrum which requires large composting units and also receives undigested organic material to increase the carbon ratio. And of course the shallow soil pit latrines like Fossa alterna that receive soil additions are good composters. UDDTs are not composting toilets and only store faeces and the possible additive (ash, saw dust, lime, etc). If kept dry these produce very little odour. Composting is carried out as a second step to create thermal conditions to kill pathogens and produce the compost for reuse.

Arno Rosemarin PhD
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  • christoph
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

So I can see that it might be worthwhile to define better what exactly is a composting toilet. I referred my comments to the "Clivus Multrum Type" composting toilet which are the only ones I really know. Due to their large composting compartments I do prefer UDDT, but that is another story.

CP
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  • KaiMikkel
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

To pick up on what Arno pointed out, I recall that when a few years ago now I researched which kind of ecological toilet I would buy or fabricate I was immediately turned-off to what is generally in the US at least thought of as a "composting toilet". The image that I presume most often comes to the average US resident's mind in conjunction with this term (no doubt resulting from the combination of a preponderance of states that permit only NSF-certified models and NSF certified models typically being these antiquated styles) is an all-in-one white molded-plastic version typified best by most of the "self-contained" models that are retailed under the SunMar, Biolet and Envirolet brands.

I myself was initially drawn to this type of toilet based on the desire for a waterless toilet and the need for a standalone version (this need resulting from the limitations of the structure in which I wanted to install the toilet) but I was quickly dissuaded from this toilet-type by the abundance of user reviews that complained to no end about the smell and the fetid mess and the logistical nightmare that this combination produced.

Looking back , I suspect that at least in most cases, three major factors were to blame. One, the basic lack of regulatory oversight compounded by poor testing standards. Two, manufacturers who persisted (and still persist!) in selling technology that was never designed for full-time use (being instead more appropriate for only very modest use like at remote cabins visited only occasionally and/or seasonally) to people who it was obvious were planning to put it into full-time service. And, three, consumers buying into the marketing hype and failing to due their homework (something that, admittedly, prior to the internet was not an easy thing to accomplish, particularly when it came to such niche products). As I read reviews gleaned from forums, blogs-posts and consumer ratings I was shocked by the general volume of poor user reviews and by the particular prevalence of vehement characterizations of these kind of toilets by people who had purchased them in good faith but who had run headlong into individual companies and an entire industry that seemed unwilling to meet them even half way (and which it appears still operates largely in the dark and on the margins).

In marked contrast, and based on the fact that I couldn't locate even one poor review of a UDDT ('all-in-one'-style or otherwise), that's what I ultimately opted for. Its unfortunate, but I'm sure that I am not alone when I say that this sad history is something that I as a toilet-activist have had to confront in my advocacy work. Its a dark stain on the history of sustainable sanitation and one that I think deserves more widespread attention. After all it can be a hard sell to convince people that sustainable sanitation is feasible when the history is complicated by the terrible experiences of so many real world users. And due to the fact that these kinds of toilets are still on the market (!) only further compounds the problem. To be honest, I'm of the opinion that manufactures have dodged a class-action-sized bullet when it comes to these kinds of toilets and that they (the offending toilets) should be immediately outlawed, both to protect the public but also our sector from further harm.

Kai Mikkel Førlie

Founding Member of Water-Wise Vermont (formerly Vermonters Against Toxic Sludge)
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  • joeturner
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

I think we need to look more closely at the test composting toilets used in these studies.

Hill et al. were looking at composting toilets in remote sites in North America where faeces fell into a chamber below, and was emptied on a semi-annual basis. They concluded that overall these did not compost.

Tsang Pui Ki's doctoral thesis looked at two models - one a Naturum urine-diversion toilet, where separated urine and faeces fall into chambers below. The other allows mixed materials to fall into a 'dual layer' container. Both were found to be partly or largely anerobic.

Anand and Apul reviewed a range of composting toilet designs including the simple commode self-contained, centrally tanked and latrine style like the Clivus Multrum. Examples of instillation of Clivus Multrum are given - such as C.K. Choi Building for the Institute of Asian Research at University of British Columbia - but states that

However, currently, the leachate is drained to the sewer and the compost product is disposed of in a sanitary landfill because they do not meet the local regulatory environmental and health and safety standards.


There is no particular reason to suppose that the Clivus Multrum model of composting toilet is overall aerobic and therefore that it will be effective at destroying anaerobic pathogens. Even efforts shown in the doctorate thesis mentioned above, which included forms of aeration (mechanical and forced) still produced anaerobic conditions in the test composting toilets.

Composting toilets, in and of themselves - even if there are some models which are better than others - should not be considered to be an effective pathogen destruction system.
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  • cecile
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

Hi everyone,

There are many composting toilets in France in individual houses. They are basically non separation bucket toilets and a bulking agent containing cellulose is added after each use (most of the time wood chips). It is the balance between the 3 components urine- faeces -cellulose and the presence of air (hence wood chips rather than saw dust) which allows the non formation of odor by blocking the transormation of nitrogen into amonia (preventing urease). This phenomenon is explained on Eautarcie's website on the page dedicated to BLT (bio litter toilet) :
" we must first prevent urease – an enzyme in our excreta – from transforming precious organic nitrogen into ammonia, unusable for humus synthesis. This phenomenon was first understood thanks to laboratory observations [4] : that plant cellulose inhibits the enzymatic reactions that mineralize dejecta's organic matter. Now, these reactions constitute the origin of obnoxious smells. An idea became obvious : add plant cellulose to our dejecta in order to block enzymatic reactions, and in so doing, prevent odours. Another benefit of this gesture is to increase our dejecta's carbon / nitrogen ratio to a level that is ideal for exterior aerobic composting. [5]."

[4]
Réf.: NIMENYA H., et coll., Ann. Méd. Vét., vol. 143, pp. 409-414 (1999)
[5]
Our dejecta's C/N ratio is about 7, whereas that of plants is between 200 and 300. To start composting, the C/N ratio should be around 60. Combining animal-sourced nitrogen (dejecta) and plant carbon (the litter) creates the ideal conditions for humus formation, without unpleasant odours.

An important detail: the inhibition of enzymatic reactions can only take place in a moist environment, therefore in the presence of urine. This is the reason you must absolutely not separate urine from faeces. Another important detail : the introduction of plant cellulose in the BLT's process (i.e. the litter) must occur immediately after defecation or urination, to prevent the start-up of mineralization."

This system works very well and according to my experience even after a couple of days of use there is still no smell in the toilets. Users then empty the bucket into a normal garden composter and mix the content with kitchen and garden waste".

This works very well at an individual household scale and because users of such a system are willing to take care of their toilet system regularly and are carefull to maintain the balance that will prevent the odour formation.

One factor can disturb this balance, that is the presence of too much acidity that is why resinous wood (such as pine trees) are not advised for the wood chips as this will create smell.

Cecile

Cécile Laborderie
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  • arno
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

A little more on the Clivus multrum. Joe was mentioning that the process may not be entirely aerobic and not hot enough to kill pathogens. But the interesting thing is the Clivus was originally designed to mimic natural forest soil and this it does well, retaining aerobic conditions mainly due to the ability to drain properly and the fact that it contains worms and other soil organisms. Pathogens drop off in time since this is an alien environment; they can't compete in the soil environment. I would say the only risk is probably helminth eggs. But even these will have a hard time surviving a moist and moldy soil environment.



This from www.clivusmultrum.com/science-technology.php
which also describes the nitrogen cycle, and the fate of pathogens in this non-thermal soil ecosystem.

Composting Science.
Composting is the bio-chemical decomposition of organic matter by aerobic organisms, i.e., organisms which get oxygen from the atmosphere and give off carbon dioxide. Composting takes place in all soils which support plant and animal life. The compost toilet employs the same process in the controlled environment of the compost chamber.
This process is distinct from anaerobic decomposition, which takes place naturally in water-saturated environments such as swamps, and is typical of septic tanks. Anaerobic, or liquid-saturated, conditions produce methane and the offensive odors associated with septic systems.

Organisms found in the composter include bacteria, actinomycetes, fungi, arthropods, and earthworms and are added manually once the system is operating. Energy, carbon dioxide and water vapor are released by the organic matter in feces through the activity of the composting organisms. A less chemically complex, more chemically stable substance, rich in organic matter, is produced. Feces volume, which is mostly water, is reduced by over 90%.

Temperatures in the compost toilet remain in the middle, or mesophilic, range (65-113°F) and don’t exceed 100°. Potential pathogens in feces are, therefore, not destroyed by heat. Those pathogens that require an aqueous environment die quickly in the non-saturated condition of the compost chamber. Others die because of the intense competition for nutrients; still others are consumed by predators which populate the system. The biological content of the dry end-product is similar to that found in topsoil. As a measure of its stability, the dry end-product from the Clivus Multrum contains less than 200 MPN (Most Probable Number) of fecal coliform per 100 grams. This meets the level required under National Sanitation Foundation Standard 41 for Non-saturated Systems. The dry end-product contains a wide array of plant nutrients and is intended to be used as a fertilizer/soil conditioner. Its use may or may not be regulated by local authorities.

Urine is also transformed by the activity of microorganisms. As compared to feces, urine contains most of the nitrogen from food. The primary form of nitrogen in urine is urea. Left alone, urea will degrade into ammonia and carbon dioxide. Bacteria in the compost unit (specifically Nitrobacter and Nitrosomonas) prevent this degradation and, instead, convert urea into nitrite and nitrate. That these are forms of nitrogen required for plant growth indicates the value of the compost toilet for nutrient recycling. The liquid end-product from the Clivus Multrum contains less than 200 MPN of fecal coliform per 100 ml. This also meets the level required under National Sanitation Foundation Standard 41 for Non-saturated Systems. The nitrogen-rich liquid end-product is intended to be used as a fertilizer. Use of the liquid-end product as a fertilizer may or may not be regulated by local authority.


Arno Rosemarin PhD
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  • joeturner
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

Can you point me to studies and not just polemics by the manufacturers, Arno?

Drainage will certainly help, but I'm not really convinced the process is reliable enough to ensure all parts of the faecal compost are fully aerated and therefore pathogens are adequately destroyed.

The only way to do this is to turn outside, I believe. Any compost heap left unturned will have areas of anaerobic conditions where pathogens can survive.
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

Hi Joe
But of course. We spent some years on these questions within the EcoSanRes Programme.
Here first is an excellent summary by Dorothy Spuhler from Seecon in Switzerland.

www.sswm.info/content/dehydration-and-storage

and is in part based on the EAWAG Compendium by Tilley et al.:

www.sswm.info/sites/default/files/refere...evised%20Edition.pdf

and includes the following table from the EcoSanRes work by Schonning and Stenstrom. www.sswm.info/sites/default/files/refere...osan%20systems_0.pdf

This table summarizes work on pathogen die off under ambient temp storage, alkaline conditions, and thermal composting.



This led to the breakthrough work by Björn Vinnerås where pathogen (and Ascaris) inactivation was optimised by dessication, alkalinity (ash and oyster shell additions) and urea additions (creating toxic ammonia conditions) under lab conditions. aem.asm.org/content/79/7/2156.full

Conclusions.A combination of factors (pH, desiccation, and ammonia content) showed promising results for sanitizing feces. Maximization of individual effects of those factors in a combined process can make it possible to produce a safe material in a low-cost and low-maintenance technology suitable for application in urine-diverting dry toilets.


These are all components taken from natural processes that occur in soil systems.

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  • joeturner
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

Page 72 of Tilley et al 2014 on, I believe, the Clivus multrum

In practice, these optimal conditions are difficult to maintain. As a result, the output product is often not sufficiently stabilized and sanitized, and requires further treatment


This is exactly what I believe about this kind of composting toilet. Where there is no batch monitoring, the system cannot be said to be sufficiently reliable to produce stabilised and sanitised faecal compost suitable for reuse.

In my view it is misleading to imply that the breakdown of faecal compost is mimicing forest soils, in a situation where there is no actual soil and it is all organic matter. No soils, other than peat soils where acidity prevents full aerobic organic matter breakdown contain that much organic matter.
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  • hajo
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

christoph wrote: So I can see that it might be worthwhile to define better what exactly is a composting toilet. I referred my comments to the "Clivus Multrum Type" composting toilet which are the only ones I really know. Due to their large composting compartments I do prefer UDDT, but that is another story.

CP


Sorry, Christoph, for 'Nit Picking' but UDDTs (under their current designs and operations) are NOT composting toilets therefore you should not prefer UDDT due to their 'large composting compartment'. They are de-hydrating toilets as the name says which in itself is opposite to composting (which requires a specific moisture content).

Whenever people call UDDTs 'composting toilets' we have to object!

ciao, Hajo

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  • arno
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

Hi Joe
You may be right. I think this is the case for most short-term batch type composts where turning is not normally carried out. There will never be 100% die off of pathogens. A secondary step such as further drying and storage or even further composting or heat treatment should be carried for public toilets for these rapid conmposters.

For household-based systems where the compost remains in the household garden, the risk of disease from reuse is very low. And don't forget the aspect of how compost is to be used in gardens. It is the soil that is receiving the compost and that functions as an additional treatment. So sensible risk assessment is necessary, unfortunately little work has been done on this.

But the Clivus is different from anything else. It stores material for years prior to reuse. The original models went for decades prior to emptying.

The Fossa alterna produces sweet smelling soil and has similar levels of organics that the Clivus has.

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  • joeturner
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Re: What do we know about odorous gases from composting toilets (or from composting in general)?

OK, if material is stored for decades, that might be a different thing - but how many ecosan and composting toilet programmes plan for storage for that length of time?

It is true that soil application acts as another barrier, but the risk assessments (which I agree are inadequate) that we have suggest that it is the emptying and handling of potentially imperfectly composted faeces that may be high risk.

Microbial Exposure and Health Assessments in Sanitation Technologies and Systems. 2011 Stenström et al fig 8 page 51

I also think that the issues are different in North America, Europe etc than applications elsewhere for important reasons: the low level of endemic faecal pathogens in the population, the widespread availablility of healthcare, better overall hygiene awareness etc.

Hence I can accept that composting toilets in Elisabeth's garden, or those advocate by Kai in the USA etc are unlikely to be a major health hazard - whilst at the same time believing that it is an inappropriate technology in many other situations.
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