I'm attaching a old (probably, 1981) paper (in MSWord format) by my AIT friends on bacterial dia-off kinetics. Though, it is about waste stabilization ponds, it gives a good insight on the die-off kinetics.

Sectt: Please check, as always, for copyright issues.

F H Mughal

Hi

My manager, Jay Bhagwan from Water Research Commission (South Africa), asked me to add some information here - see the attached file. It is a bit of topic but as mentioned in earlier post, Chris Buckley and Dave Still's teams are currently doing research on the pour flush toilets. There are also improved designs being tested that use a low flushing cistern.

I have attached the report from initial trial - Elisabeth initially started a thread elsewhere(forum.susana.org/forum/categories/141-ot...dea-for-south-Africa).

The WRC is currently funding a 3year study tracking the characteristics of Pour Flush Sludges. We not there yet to release any data. Maybe in the next 6 months we will be able to provide some scientific data. The work is done by Chris Buckley’s team at UKZN

JN Bhagwan (Jay)
Executive Manager - Water Use and Waste Management
Water Research Commission
Private Bag X03, Gezina, 0031, South Africa
www.wrc.org.za

Dear all,

This is an interesting topic and as Elizabeth already mentioned it is very hard to get solid research data. Maters Thesis topic for anyone? .

Some random ideas and observations on the subject:

I have opened a few pits in Nepal and they are definitely not all well draining. Most of the ones I saw were in-use and contained a watery slurry. However I would expect them to dry out during the 3 years storage period. Further, the pits I saw were all over-sized so the storage time is more likely to be 4 to 5 years.

I think emptying these pits using hand-tools, gloves and gumboots (combined with good washing practices) would provide an acceptable level of risk, considering that the main pathogens surviving would be helminth eggs.

As long as there is no good data on pathogen die-off in these kinds of pits I think we should recommend that the soil from these pits should be used only for planting trees. (Oversize the hole you dig for the tree and fill it half with the produced "compost".)

Regards

Marijn

JKMakowka wrote: Composting is really only more efficient if high temperatures are reached, and the risk remains that material not properly mixed never reaches those temperatures.

I totally agree that co-composting needs to be done properly to be effective.

Thus IMHO long term storage for natural die-off is probably the safer bet.

I'm not sure there is the research that backs this up. Whilst there is die-off, I'm not sure it is proven that this is effective enough of the time to be a general rule. And, presumably, the same qualifications about co-composting can be made about storage - namely that suboptimal storage conditions will not kill off pathogens as expected.

I still believe that meso scale composting operations are always going to be more manageable and reliable than dispersed and unmonitored individual systems.

The findings of the above study are actually very interesting and I think somewhat correlate to what I started to discuss here: forum.susana.org/forum/categories/51-ann...-toilet-map-of-india
(e.g. that there is a strong "cultural" -for the lack of a better word- component for the slow uptake of latrines in India especially).

In don't know how to interpret this report, but it appears to contradict some of what we were hearing from Pawan above - namely that the systems were left unused because open defecation was 'prefered' rather than that the systems were full.

Composting is really only more efficient if high temperatures (~60 degree celsius) are reached, and the risk remains that a part of the material that is not properly mixed never reaches those temperatures.
Thus IMHO long term storage for natural die-off is probably the safer bet.

The findings of the above study are actually very interesting and I think somewhat correlate to what I started to discuss here: forum.susana.org/forum/categories/51-ann...-toilet-map-of-india
(e.g. that there is a strong "cultural" -for the lack of a better word- component for the slow uptake of latrines in India especially).

Hello Pawan, thanks for this.

I have just been reading this 2013 Plos One paper looking at the impact of TSC in Orissa. It would be interesting to hear your comments.

I thought these results were quite telling:

The most common reasons why latrines were not in use was that individuals within households preferred open defecation (29%), the latrine was not complete (28%) or using a latrine was deemed inconvenient (20%). Other reasons for non-use were that the latrines lacked privacy (23%), were used for storage (22%), were broken (17%) or blocked (9%). Only one household ascribed non-use to water being too distant, and only 4% of households reported that it was too difficult to empty the pit.

Given those contraints, I wonder how likely it is that sludge will safely be contained for three years in a village context.

There is no other better technology known having natural die-off of all pathogens from sludge.

I'm not sure about this statement. Aerobic co-composting is usually considered to be more effective than latrine storage.

Hi

Thanks to all who participated in the discussion and provided valuable inputs. Comment from Florian is very right- after three years,contents of the toilet pit should be termed as almost pathogen free rather than completly pathogen free- mainly due to helminthic eggs. It is, however, accepted that after three years such sludge is free from bacterial pathogens.

Elizabeth very rightly pointed out that contents of single pit toilet can't be handled as it contains active pathogens. In fact, it has been observed in India that Under the Total Sanitation Campaign (TSC),millions of single pit household toilets were implemented in rural areas. Most of them became non-funtional after 2-3 years, when the single pits were filled. Due to smell and pathogens such pits can't be emptied immediately.Under such condition, households restored open defecation.
Manually emptying of such pits would attract penal provision under Liberation of Manual Scavenging Act of the Government of India and mechanical device is rarely available in rural areas. Therefore single pit toilets need to be discouraged.
There is no other better technology known having natural die-off of all pathogens from sludge.

There is an advertisement from Department of Biotechnology, Govt. of India in collaboration with Bill and Melinda Gates Foundation seeking proposal for“Reinvent the Toilet Challenge - India”, a program directed at addressing the problems in sanitation and specifically targeted towards Indian innovation and creativity. I would like to submit proposal. Such advertisement was attached in my last posting (forum.susana.org/forum/categories/95-cal...nda-gates-foundation). It is an international experession of Interest. Any interested professional/ institutes may send his/ her idea to submit a joint collaborative proposal to the Ministry/Foundation
Pawan Jha

I agree with the others - that there is a lack of useful literature on the subject. But this is partly because few seem to fit the pieces together - what we really want to know is how many helminths are retained by a given system, and then some kind of risk analysis on the safety of the material, such as using a Monte Carlo risk assessment .

From what I've read, you'd need very specific circumstances to destroy all helminths. There seem to be different numbers offered for survival for different standing times, but it is probably fair to say that the major risk is to sanitation workers (and this is significantly reduced with 2 or 3 years of storage) in emptying the facilities, hence Florian's advice is good.

muench wrote: But a pit that has rested for 3 years, you are saying it does give full kill of helminth eggs? I have read this claim here and there but is there a good scientific study about it somewhere, do you know of one?

No, I don't say that 3 years in a pit will 100% kill all helminth egg (and I am not aware of any study saying so). Just as we don't state this for 3 years old material from UDDTs or other facilities.

The recomendations we commonly use for reuse of excreta say it is acceptable to use after 2 years because almost all pathogens are dead then, although some pathogens may still remain, and therefore other additional safety measures are recommended.

Of course real die off in the different facilites may be different, the conditions in a wet and anerobic pit may contribute more or less to helminth die off than the dry and aerated conditions in a UDDT vault or storage heap. I am not sure if there are any studies on this. But either way, this would be theoretical to a large extent, because in practice the factors that are different (humidity, temperature, oxygenation) cannot be well controled anyway. The only factor that can be well controlled is storage time, this is why we use time for practical recommendations on reuse. The time used (e.g. 2 years) corresponds mostly to the natural die off time of the pathogens, so I think this can be safely applied as well to sludge in pits.

Agree that "pathogen free" is a too strong statement, but "almost pathogen free" would be allright.

Best, Florian

Thanks for your reply, Florian. Even before I read it, I thought that I should change the title of the thread to twin-pit alternating (which I have done now).

So it's very important to be precise that a single pit pour flush toilet cannot lead to pathogen-free sludge (sludge being emptied when pit is full, i.e. directly after last use).

But a pit that has rested for 3 years, you are saying it does give full kill of helminth eggs? I have read this claim here and there but is there a good scientific study about it somewhere, do you know of one? (like those rigourous studies from South Africa for VIP sludges and UDDT faecal matter; keeping in mind that enumeration of viable eggs is not trivial, as we have discussed elsewhere on the forum, e.g. here: forum.susana.org/forum/categories/97-ena...dge-enumeration#2912 and here: forum.susana.org/forum/categories/17-fer...s-in-a-reuse-context).

I could probably start a long Google search on this, but if someone has such a study at their fingertips, I would be grateful (i.e. about helminth egg die off in sludges from twin pit pour flush toilets after 3 years of resting). Because otherwise, I remain unconvinced.
(but I fully agree that if the multiple-barrier concept is applied, like you pointed out, then it can be safe enough in the end; I just don't like the "sweeping claims" about safety).

Regards,
Elisabeth

Hi Elisabeth

The work done by David Hawksworth and Colleen Archer did indicate that Ascaris eggs can survive much longer in UD toilet vaults than was generally believed to be the case, but I don’t think they would have tested sludge as old as three years. I have also heard reference to viable Ascaris ova in the bottom layers of “old” pit latrine sludge, but as far as I know this sludge was sampled from toilets that were still in use so I don’t think it would have been possible to prevent cross-contamination from new layers to old layers, especially during the emptying/sampling process.

See also:
Buckley, C., Foxon, K., Hawksworth, D., Archer, C., Pillay, S., Appleton, C., Smith, M., Rodda, N. (2008). Research into UD/VIDP (Urine Diversion Ventilated Improved Double Pit) toilets, prevalence and die-off of ascaris ova in urine diversion waste. Report to the Water Research Commission by the Pollution Research Group, University of KwaZulu-Natal, South Africa.
susana.org/lang-en/library?view=ccbktypeitem&type=2&id=385

and:
Moodley, P., Archer, A., Hawksworth, D. (2008). Standard Methods for the Recovery and Enumeration of Helminth Ova in Wastewater, Sludge, Compost and Urine-Diversion Waste in South Africa. Report to the Water Research Commission (WRC), WRC Report No. TT322/08, South Africa.
susana.org/lang-en/library?view=ccbktypeitem&type=2&id=420


In my work we have looked at the fate of Ascaris and other helminths in sludge that has been buried in soil. Here we find that complete die off does take place within three years. I have not yet had the opportunity to record the fate of helminth ova in standing pour flush vaults.

See also:
Still, D., Louton, B. (2012). Piloting and testing the pour flush latrine technology for its applicability in South Africa. Report to the Water Research Commission, WRC Report No. 1887/1/12 ISBN 978-1-4312-0289-8, South Africa.
susana.org/lang-en/library/library?view=...eitem&type=2&id=1635


Regards

Dave


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Note by moderator (EvM):
We had a previous discussion about pour flush toilets in Africa here:
forum.susana.org/forum/categories/39-mis...dea-for-south-africa