Hi Joe,
Certainly we could debate what time period should be deemed safe, but what is not in question is that time does kill off pathogens.

There also needs to be some context around what is "safe". Safe to be handled and spread around? Safe to put around food crops that will be eaten raw? Safe to sell as a product? These are all different, I'd be happy to spread compost full of helminths around some trees, I'd just wear gloves and maybe a dust mask to be safe. What I'm most interested in is a product safe to spread around in crops, but even this safety level varies according to whether the crop is to be cooked or eaten raw.

Lets consider low temperature composting in the most primitive of "compost toilet" systems, the twin pit, where decomposition occurs and capacity is sufficient for an agreed (based on science) safe resting period. After which period, the compost is deemed safe to handle and spread around the carrot crop. The product coming from this system is in stark contrast to sludge from a single pit, where pathogens are not killed because decomposition doesn't take place, or faeces sitting in a pool of water or urine without decomposing. Or ecosan compost after 6 months rest (the helminths are still all there), or even dried faeces where pathogens are simply re-activated when moisture is reintroduced.

Risk is never completely removed, whether hot or low temperature composted...

get a parameter wrong and the result will not be acceptable

Both have parameters that if not met (e.g. human error) increase the safety risk. I'm more comfortable with time than temperature, even if I have to wait 5 years for assurance, because

you can't be sure that the (hot composting) process has been done correctly

cheers
Dean

What confuses me is why anyone would want to continue with a low temperature "composting" system that everyone here seems to be in agreement does not kill pathogens sufficiently.

What is so hard about designing systems that a) remove excess liquid b) ensure the material is mixed and aerated c) has sufficient carbon so that d) temperatures of over 55 degrees are reached for the (relative short) period to kill pathogens.

As I said above, it isn't really difficult to do in a windrow. One would think it isn't particularly difficult to design something with augers and stirrers and air pumps in more enclosed spaces - although I am not an engineer and couldn't do it. Personally I would always go for meso-scale outdoor composting sites.

So why persist with the fiction that one can add small/random amounts of carbon in a space with limited air and with much of the faeces sitting in a pool of water or urine - and produce compost that is safe to be handled and spread around?

It isn't that difficult to understand, is it? It is just a microbiological system like making cheese or beer - misunderstand the process or get a parameter wrong and the result will not be acceptable. And if you can't be sure that the process has been done correctly, then you can't assume that the product is safe.

Isn't that obvious? What am I missing?

Well let's see about this.

First the WHO standards are not "recent literature" given that it was published in 2006 and we are now in 2019 - with recent studies of the actual system you are describing rather than generalities based on very old studies.

Second of all, table 3.9 of the WHO standard, page 45 gives an absolute maximum of 7 years in soil. Apparently based on a study from 1983.

Table 3.5 does indeed give a duration for survival on page 38 based on a study from 1994. But the text immediately below that table suggests that the "storage conditions will affect die off rates" and that one study from Denmark showed unacceptable risk even after 12 months and another from El Salvador showed Ascaris survival of 600 days in a latrine with a pH of 9.

Is 90% die off of Ascaris loading in faeces (in places where it is common and endemic) safe? Have you conducted Quantitative Microbiological Risk Assessment to find out?

The only way to be sure that Ascaris - and other pathogens - have been destroyed is with a reliable way to get the totality of the faeces to a high temperature.

Hi Joe,
The WHO guidelines for the safe use of wastewater, excreta and greywater Vol 4 part 1 table 3 gives die-off of Ascaris (90% inactivation) as 125 days +- 30 days for faeces and 625 +-150 days for soil. I suggested 2-3 years which isn't far off what is published for soil.

Ascaris was the slowest to die off, followed by Cryptosporidium then Giardia. The point I am making is that pathogens die over time, and whether that time is two years or five years, this should be acknowledged.

cheers
Dean

Hi Geoff,
Commercially produced compost should clearly meet standards for pathogen levels to protect the consumer. This is irrelevant to compost from toilets, unless that compost were to be sold.

Pathogen destruction through time is highly dependent on site, moisture, pH, and temperature.

"highly dependent" is perhaps an exaggeration. Dependant yes, but decomposed human excreta (compost), held for a specified period of time within a reasonable range of moisture levels and temperatures is universally achievable. Perhaps Alaska would need longer than Florida, but my point is that I'm a lot more comfortable with compost that has rested for a conservative time period such as 5 years, than with a Jenkins batch-produced compost because I simply cannot be assured that the variables were adequately controlled for consistent heat right through for the required period of time.

We all know a continuous flow system can't rest and I'm not suggesting any period of rest is achieved with such a system. In contrast, twin batch systems just need to achieve whatever time period is required before switching over. Whether that time period is deemed to be two years or five years is just a design/capacity issue.

There have been a lot of studies published in the literature in the last 18 months looking at pathogen survival in composting toilet systems. Enough that I think we may need to conduct a widespread review of the Wikipedia page to take account of them - some including risk (using Monte Carlo systems) DALYs of handling and using the materials etc.

I can't find anything suggesting that Helminths are completely destroyed after even 2 years of post-treatment storage, even when that treatment is in a fully managed facility never mind a composting toilet system.

I will keep looking.

Ok Dean - show me a study where faeces "composted" at less than 50 degrees followed by two years of storage killed off all helminths.

2-3 years time is not a reliable mechanism in a working toilet at a refugee camp. Think real world applications. Doesn't get around the issues with short circuiting.

Fascinating that people are so strangely emotionally attached to the term "composting" toilet. Worthy of psych study.

Geoff Hill
Toilet Tech

Hi Joe, the scientific literature is very clear that pathogen levels reduce over time in decomposed human excreta.
Even the most robust of these, helminth ova, are all gone in two to three years. Pathogens are reliably destroyed with decomposition followed by storage.
cheers
Dean

I agree though that anyone is free to call their system a "composting toilet" if they want to ignore all the recent studies in the scientific literature and redefine terms.

I'd argue that if we know that these systems do not reliably destroy pathogens, they can't honestly be described as "sustainable sanitation".

The US Composting Council (USCC) recently updated the definition of Compost to include the thermophilic process. They did this to protect public health from various compost producers who were negligent in adhering to pathogen reduction processes yet still able to market their (questionable) material as compost. Thank you to Ron Alexander.

wasteadvantagemag.com/uscc-efforts-resul...by-regulators-group/

Pathogen destruction through time is highly dependent on site, moisture, pH, and temperature. Time to destroy ascaris ova can be multiple years. This is not a reliable method. Most composting toilets are operated as continuous flow. Material added to top seeps down to bottom (oldest material) with urine / drainage. So time is not really achieved even here.

If material is pulled out to batch treat by "time" the operator might as well do a "Jenkins" batch compost process by adding bulking agent. Heat destroys pathogens many orders of magnitude faster than "time" treatment.

Geoff Hill
Toilet Tech

High temperatures absolutely is required to kill some of the worst faecal pathogens in a faecal composting system.

Other effective systems exist. But "composting" at low temperatures with storage isn't one of them.