[Stoves] Water Disinfection - Mix Boiling Water and Unheated Water to Pasteurize

Tue Oct 15 15:37:00 CDT 2019

Dear Kevin

I think some caution should be applied to the darkness result. The claim was not that it disinfects water, it was that it is better than nothing. So it would be more appropriate to include in any report what was in the water, what was killed and what survived, and at what temperature.

I don't think it will help any proposed case to claim the darkness does nothing, nor that the proposed mixing does everything because experts will know neither claim is sustainable. Even boiling the whole volume for one minute won't disinfect it of everything found in water.

I have another observation for you which I invite Dale in particular to comment on. If you want any target temperature for the whole volume of water, and you heat a portion of it to a higher temperature then mix it, it will take more energy than to heat the total volume to the target temperature. The reason is the heat transfer efficiency drops as the pot temperature rises.

Given that the goal is to have all the water at some temperature lower than boiling, just heat the whole thing to destroy whatever is in the water at that locale. Context applies.

If stoves would like to work on something new I suggest water heating for domestic use has been overlooked as a specialized application. There is no fundamental reason for a wood-fired water to have an efficiency of less than 65% which is well above the ISO tier 5 requirement for cooking stoves.

If you observe how much fuel is used for water heating (not cooking) it is often a  large fraction, a majority. For Indonesians, 40% of the people use wood 100% for water heating and none for cooking.

Let's make water heating and pasteurization is a hot topic.

Regards
Crispin

PS Please take a moment to remember Paul Polak who passed away this week aged 86.  He founded International Development Enterprises among other things. He was very active in promoting healthy water access.
From: info at sun24.solar
Sent: October 15, 2019 11:31 PM
To: stoves at lists.bioenergylists.org; webmaster at solarcooking.org; dandreatta at sealimited.com
Reply to: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] Water Disinfection - Mix Boiling Water and Unheated Water to Pasteurize

cc:  Tom Sponheim and Dale Andreatta

A lab in Kenya tested 1:1 and 2:1 parts boiling water to unheated contaminated water, mixed, cooled for 30 minutes and mixed again.  Both tested negative for Total Coliform, Fecal Coliform and E Coli.  Here is the report<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F1PifTmJ6haJYV13zs0zzV61P0xFXyLSB2kS9fs6vDH6E%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7C014f05101b2d4728aa9f08d75184c64b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637067503016072788&sdata=pua4c597vvSJaslez4K49eP%2Fqfb1QRNTidkL0gOtgXc%3D&reserved=0>.  This is very encouraging.

The Kenyan lab recognizes the importance of these results and intends to perform more testing on its own with a goal of publishing in a trade journal.  I hope to have a lab in Uganda do similar testing soon.

The Kenyan lab also test disinfection by darkness.  Five days of complete darkness failed to disinfect the water.

Kevin

On Mon, Sep 23, 2019 at 5:59 PM Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
Volunteers in Technical Assistance.

The head was Don Feil for some time recently. I am not sure if he still is. His phone mailboxes are full.

US-based people volunteer their time to solve problems encountered by overseas people. It did a lot of positive things.  They produced the first (rather defective) WBT test, with them mediating three organisations, them, plus one in France and one in Germany.   They put out a number of publications including the VITA Technology Handbook and the microfiche library of everything the Village Technology Sourcebook. Back in the early ‘80’s that was the basis of any good appropriately technology centre library.

Cecil Cook and I co-founded the Transkei Appropriate Technology Unit in 1982 and there wasn’t all that much to go on, besides the ITDG publications.

So, there is some discussion of water storage here.
https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0006364<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fjournals.plos.org%2Fplosntds%2Farticle%3Fid%3D10.1371%2Fjournal.pntd.0006364&data=02%7C01%7C%7C014f05101b2d4728aa9f08d75184c64b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637067503016082799&sdata=SX9grEu3IIdSRn2uKwCCg0bciBN83KYhkGbNkmIkENo%3D&reserved=0>

Conclusions
“All five water treatment methods can remove or inactivate cercariae in water, and hence produce cercaria-free water. However, reliable design guidelines for treating water do not exist as there are insufficient data. Overall, the review found that cercariae are inactivated when storing water for 10–72 hours (depending on temperature), or with chlorination values of 3–30 mg-min/l. UV fluences between 3–60 mJ/cm2 may significantly damage or kill cercariae, and sand filters with 0.18–0.35 mm grain size have been shown to remove cercariae. This systematic review identified 67 studies about water treatment and schistosomiasis published in the past 106 years. It highlights the many factors that influence the results of water treatment experiments, which include different water quality conditions and methods for measuring key parameters. Variation in these factors limit comparability, and therefore currently available information is insufficient for providing complete water treatment design recommendations.”
I think that is information enough to start.
Regards
Crispin

From: Stoves <stoves-bounces at lists.bioenergylists.org<mailto:stoves-bounces at lists.bioenergylists.org>> On Behalf Of K McLean
Sent: Monday, September 23, 2019 5:39 PM
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org<mailto:stoves at lists.bioenergylists.org>>
Subject: Re: [Stoves] Water Disinfection - Mix Boiling Water and Unheated Water to Pasteurize

I searched for a couple hours and found nothing.  I'll keep trying.  What is VITA?

On Mon, Sep 23, 2019 at 5:13 PM Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
Dear Kevin

I support your support to support those who have nothing.  Better is something.

Is it possible that VITA has done work on this?

It is so essential that it seems unlikely there is no work on it.  It is not something I follow closely.

Perhaps a brief search will turn up someone who knows someone who knows.

Regards
Crispin

Your disinfection by darkness method should be easy to test in a lab.  If successful in the lab, I can think of many ways it might be easily implemented.

Despite decades of effort, 2.2 billion people (67%) in the 60 developing countries analyzed in this study<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC2813171%2F&data=02%7C01%7C%7C014f05101b2d4728aa9f08d75184c64b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637067503016092804&sdata=KWKqClDFH%2Bnoww%2Bont3VvSQNSe2IX4XMACL%2BRlDVazs%3D&reserved=0> do nothing to treat their water.  Of those that treat, 500 million use adequate methods.

If you think your disinfection by darkness method has potential, help find a lab and I'll pay for the testing.  It doesn't have to be the best solution, just a good method that can be quickly disseminated.  Let's not let the perfect be the enemy of the good.

Kevin

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