[Digestion] Use of centrifugal pump for transferring feedstock into digester

[David]

Doe, David, Dr. Karve,


On 11/16/2013 6:22 PM, Joe Crescenzi wrote:
> Centrifugal pump works fine for us here on a 1000 M³ digester. 
> Maintain the pump below the level of the holding tank to minimize 
> air entry. We do incorporate about 35% liquid digestate from the 
> digester into the new incoming slurry - before the pump.
>
> ----------------------------------------------------------------------
> From: adkarve at gmail.com
>
> Dear Dr. Fulford,
> thanks a lot for the explanation and the solution.
> Yours
> A.D.Karve
>
> On Sun, Nov 17, 2013 at 12:45 AM, David <davidf at kingdombio.com 
> <mailto:davidf at kingdombio.com>> wrote:
>
>     Dr Karve and listers, Hello,
>     Tests I tried in a laboratory which involved pumping material
>     into a digester suggested that flow velocity is important.
>


I have a hard time imagining that the type of pump used would have any 
impact on the situation. Logic would tend to make me skeptical. 
Consider that some (not all) studies of agitation have shown that 
violent or continuous agitation is not beneficial, but for any 
microbes passing through a pump, that is a momentary and probably 
minor discomfort at worst. Indeed, even if a pump or some other 
process is completely /sterilizing/ the incoming slurry-- killing 
everything, as is occasionally done with garbage or another biohazard 
substrate-- then regardless, if what is being fed is digestible, it 
will all be colonized and mostly digested during the period of any 
sensible HRT. Further, surely if centrifugal pumps, which have been 
used for years on digesters, had some negative effect on digestion, 
then this would have been noticed and exampled in the literature. I 
don't know of any such references, whereas if the effect were as 
dramatic as these reports suggest, I would think this would be a 
widely known caveat.

Thus whatever the situation is with the three digesters mentioned by 
Dr. Karve, I tend to doubt that it has anything to do with the pump, 
regardless that this is a shared characteristic. They may, after all, 
each have entirely different causes for their problems.

Of course, at best that's merely exclusionary, ruling out one 
candidate for cause, and it does not solve Dr. Karve's mystery, nor 
does it address the experience of Dr. Fulford.


d.
-- 
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

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