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Re: Re: Carbon properties
>Date: Wed, 5 Aug 1998 09:34:42 -0700 (MST)
>From: "Roger S. Miller" <rgrmill at rt66_com>
>Subject: Re: carbon
>I can't resist responding, despite the fact that this was posted to
>someone else and in a different forum :)
I knew that!:) I noticed that you likes the same matters I like, and yoiu
are particularly interested in technical, scientific aspects of aquatic
gardening.
Anyway ANY contribution is very welcome as I'm particularly ignorant and I
wanna learn as much as I can, so don't worry and please feel free to write
all your comments! :-)
>In most aquarium equipment activated carbon is just packed into a media
>chamber and water is pumped through (or around) the media. Compared to
>industrial systems there is relatively little contact between the
>activated carbon and water (unless you load it into a fluidized bed
>filter). That limits the effect of the activated carbon.
TRUE! But I think you should also consider that normally the metals
presence are lower than in all the industrial water waste purification
processes.
>After a rather brief period in an aquarium (as little as a few hours)
only few hours? I think the time first of all depends of the species of
bacteria. Nitrobacter replicate every 24 hours on the average. Anyway as
carbon offers a HUGE surface to bacteria compared with other biological
filter media the colonization time should be longer.
>the
>activated carbon can be colonized by bacteria which typically produce a
>carbohydrate slime. The presence of the slime on the activated carbon
>slows the film diffusion step to a crawl and futher limits the activity of
>the activated carbon.
TRUE! But only partially. What really happens is that the adsorbtion
activity of carbon is time limited but as the colonization of bacteria
improves the biological filtering substitutes the adsorbative action.
Typically you will find only ONE film layer of bacteria onto the carbon
surface. That speed up the decomposition of the organic moleculas
aggregated to the carbon surface and set the link points of carbon free
again to adsorb new organic compounds. A colonized activated carbon is MUCH
MORE efficient than a sterile new activated carbon.
Furthermore what makes carbon different is the total surface that it offers
to the bacteria for colonizing. If you think that new filtering media such
as EHEIM EFHISUBSTRAT or SCOTT SIPORAX offer surface of from 300 to 450 m^2
per liter, and the DUPLA activated carbon (for example) offer 540.000 m^2
per liter !!!
>I think that in industrial systems the activated
>carbon is either used as a biological rather than chemical medium,
TRUE! Another BIG difference between industrial systems and aquarium tanks
is that industry has often very effective mechanical pre-filtering (they
often work at 10 nm !!!) that helps a lot to keep the carbon surface clean.
That means a far better adsorbe power. In aquarium tanks what makes
activated carbon uneffective after some time is just all the fine particles
that close and reduce the carbon surface.
>The most common (as near as I can tell) chelating agent used in aquarium
>fertilizers is EDTA.
TRUE! In aquariums bacteria that are cabable to break down EDTA and use it
as nutrients exist even if their reproduction and propagation is very very
slow. The big, enormous surface of carbon probably can speed up this
process and if you consider that all the chelated elements that plant don't
uptake can be considered food for bacteria.... with a filtering system that
rely on activated carbon a bigger consumption is likely to happen.
Alternatively withthe same dosage of trace elements you should expect a
reduction of chelated metals into the water column.
That's all I know by now. Sorry for my broken english! :-))
Sincerely,
Luca Specchio
References:
Dr. A. Oberbremer "Fine filtering with activated Carbon" AH, 1996
Dr. Gerd Kassebber "Auch Bakterien liben es: Eisen in Aquarium" AH 1988