Deactivation mechanisms in UDDT's? (question from Uganda example)

  • birteraes
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Deactivation mechanisms in UDDT's

Dear all,

I am performing a short qualitative study on the reuse of dried fecal material of UDDT's in Uganda. For this study I investigated some samples on their bacteriological and chemical properties. This study was only preliminary and too small to be of any scientific value. However, it raised some question marks which I would like to address.

I noticed there is a very fast inactivation of for example E. Coli and Salmonella. I followed the posts on this forum on UDDT's but they mainly talk about temperatures needed for inactivation. The temperature in the sampled toilets was not extremely high (25°C - 35°C). In my opinion the very fast inactivation is due to the high pH (9-10) and the low moisture content (mostly <20%). I did not found much literature on the effect of these parameters on the breakdown of several pathogens. The most relevant documents I found up to now are the work of Faechem (1983) and the Guidelines from WHO on the reuse of excreta (2006), but these documents as well contain only little information regarding moisture and pH.

I would like to hear some opinions of people with more experience in this field on the possibility of pH and moisture content as deactivation mechanisms. Moreover it would be nice to find some more literature about it, mainly on the influence of these parameters on the deactivation of helminth eggs (Ascaris).

Thank you!
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  • muench
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Re: Deactivation mechanisms in UDDTs? (question from Uganda example)

Hi Birte,

Welcome to this forum! One parameter that you didn't mention which I think is important for deactivation of pathogens (including helminth eggs) is time. I would say in UDDTs in practice the two most important parameters are time and low moisture content. It's good if the pH is high but this would rely on the user adding something. Did the users add something (lime or ash) to increase pH in your study in Uganda?

As to more literature, I don't have anything in particular at my finger tips but I would suggest that you read through some of the previous threads in these two sub-categories of the forum:
Pathogen removal in UDDTs or in secondary treatment steps after UDDTs
forum.susana.org/pathogen-removal-in-udd...nt-steps-after-uddts

and
Pathogen removal during faecal sludge treatment
forum.susana.org/pathogen-removal-during...cal-sludge-treatment

You'll see you are in good company with your research questions. :-)

Regards,
Elisabeth

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  • birteraes
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Re: Deactivation mechanisms in UDDTs? (question from Uganda example)

Dear Elisabeth,

Thank you for your reply! You are definitely right that time will probably be the most important factor. However I think that this is not the only factor. I have some results to support that:
*In toilets that were currently in use (so the material is only stored for 2 weeks between sampling and testing) we found no E.Coli but a lot of Enterococci/Streptococci.
*In a mixed toilet (so no UDDT) we found many Enterococci/Streptococci and helminth eggs, although it was already stored for 1 year. In contrary, in the most UDDT's no Enterococci/Streptococci and helminth eggs were found after 6 months of storage (note that the prevalence of helminth eggs was not known).

According to Faechem, the amount of virusses and protozoa decreases after defecation. However, the amount of bacteria can increase if an environment is created in which they can thrive, which is the case in the mixed toilet I think.

This makes me think that the combination of low moisture and high pH also does part of the deal. I just don't know which of the two is more important and to which extent.

The pH in our UDDT's in Uganda is indeed high because ash is used as a filling material (1 to 4 cups after every defecation, depending on the habits of the users). Due to the high pH, a substantial part of the N-nutrient is lost through evaporation of NH3 during the storage process. Switching to another filling material, such as sawdust, might reduce the N-loss and therefore be favorable when it comes to fertilizing potential.
However, I am not sure if this rise in pH has a great deal in reducing the pathogens. I am glad to hear that you think out of your experience that the low moisture content is very important.

I think further research is required on this.
I will certainly follow the posts in these categories as they might contain information!

Kind regards,
Birte
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  • Tore
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Re: Deactivation mechanisms in UDDT's

What you say is correct. Faechem is the only time/temperature chart that I am aware of. As you noted there are many more factors relevant to killing all pathogens, raising and lowering temperatures in the chamber, how long to maintain temperatures, moisture content in the feces, and time are all factors. I am sure there are additional factors that could pertinent in sanitizing feces. Some eggs are extremely hardy and difficult to kill. I wish some university would take on the challenge to provide a more thorough chart on killing pathogens in feces.
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