[Stoves] Drinking straw that eliminates the need to cut any firewood at all

[Andrew C. Parker]

Andrew H.,

I am not a scientist, but I used them and was used by them, in my previous  
occupation.  I do not know what specific materials the membrane filters  
are made of these days, but it is my understanding that biofilms will grow  
on just about any surface, unless it is a biocide.  Once the pores of the  
membrane are clogged, they are almost impossible to use. Much cheaper  
(relatively) just to replace them.  That is why the RO system I was  
researching 15 years ago used pre-filters, pre-treatments and regular  
backflushing to extend the life of the membrane.

In water purification, it is very important to know what is in the water  
you are going to treat.  Knowing what is in the water can guide you in  
choosing the appropriate tool for the job.  A simple slow sand filter can  
remove turbidity and most pathogens.  A dose of chlorine will usually take  
care of anything that slips through.  I understand that there may be some  
hesitancy to use chlorine, but since it is required in the LifeStraw  
Family, why not go for inexpensive sand filtration and chlorine in the  
first place?

The thing that makes me most uncomfortable with relying on microfiltration  
is that it does not filter toxins.  Just removing the pathogen is not  
always enough.  The toxins produced by the pathogen must also be filtered  
or inactivated.  That leaves you with the choice of using chlorine or  
boiling.  Again, regular testing is the only way to know what treatment  
method is appropriate and to monitor its continued effectiveness.

Salinity and heavy metals are another topic entirely.

In researching clay pot filters, I ran across this reference,  
<http://www.relfe.com/clay_water_filter.html>, that gives a good  
description and critique.  I especially liked the comment in the critique  
that recommended concentrating on protecting water quality rather than  
water treatment.

If the target population does not currently boil, or in any other way  
treat, its water, I would think that education would, in the long term, be  
preferable to distributing free "magic tubes" in order to profit from  
carbon indulgences.  We have created a very bizarre world of late, have we  
not?


Andrew P.



On Wed, 28 Dec 2011 15:32:03 -0700, <ajheggie at gmail.com> wrote:

> Andrew, it's good to know that there are other things to consider in a
> micro filtering device. Are these problems like biofilms to do with the
> substrate offered by the filters? Are they plastic? The late Ron Rivera
> of potters for peace made water purifying jugs  with silver impregnated
> in the porous walls to act as a biocide, how would these compare?
>
> I accept that the water has to be free of dissolved mineral poisons but
> the chief problem must be pathogens??
>
> I speak from ignorance of the practicalities, though I did assist a  
> school
> trip though our local water treatment works and the final dose of a few
> ppm of chlorine was the "coup de grace" after the water was filtered then
> floculated and oxygenated. I'm spoilt because all the water from the our
> mains is potable, even though only a small percentage actually gets used
> in food , drinks or food preparation.
>
>
> On Sunday 25 December 2011 22:46:25 Andrew C. Parker wrote:
>> My
>> in-laws in Ecuador always boil their drinking and cooking water
>> (Ecuador subsidizes propane for cooking, so no wood or charcoal is
>> burned), and some people boil bath and laundry water as well (after
>> bath/shower disinfectants are a big seller).  It is nice to have clear
>> water from the tap, when it works, but by the time it reaches the
>> customer, it may still appear clear but has been contaminated with who
>> knows what.
>
> Interesting because elsewhere in this thread there is the claim that  
> water
> is not usually boiled in the target market for this lifestraw. Even then
> in your cited case there is an obvious carbon cost in boiling because
> fossil fuels are used but in the African case?
>
>
> The politics of this lifestraw presentation seem convoluted. An
> entrepreneurial company have developed the device but there is no mass
> commercial market for it, it's unaffordable in the target market. The
> people behind the distribution of the device can sell the sponsorship of
> it by issuing carbon credits, are they voluntary? It strikes me they will
> go far in the western world.
>
> AJH
>
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