You are at The Krib ->Chemistry [E-mail]

Activated Carbon

Contents:

  1. Activated Charcoal
    by Elizabeth Worobel <eworobe-at-cc.UManitoba.CA> (Tue, 7 May 1996)
  2. Brita type filter, hardness and alkalinity
    by Shane <shane-at-sure.net> (Thu, 14 Nov 1996)
  3. Carbon&Iron
    by "Justin P. Healy" <jphealy-at-sysconn.com> (Fri, 7 Mar 1997)
  4. Take the Carbon Challenge
    by Jeff & Denise Dietsch <dietsch/voicenet.com> (Thu, 26 Mar 1998)
  5. Jeff's Carbon Challenge
    by "Roger S. Miller" <rgrmill/rt66.com> (Fri, 27 Mar 1998)
  6. Activated Carbon
    by eworobe/cc.UManitoba.CA (Fri, 27 Mar 1998)
  7. Carbon properties
    by Luca Specchio <luckyluca/mclink.it> (Wed, 05 Aug 1998)
  8. Activated Carbon and Planted Tanks
    by "John Godbey" <godbey/wizard.net> (Thu, 6 Apr 2000)

Activated Charcoal

by Elizabeth Worobel <eworobe-at-cc.UManitoba.CA>
Date: Tue, 7 May 1996

Several people have asked about the chemistry of activated charcoal. 
Activated charcoal is made by burning wood or bone. It is therefore a 
complex mixture of many different types of organic compounds and 
minerals. It is likely that polycyclic aromatic hydrocarbons make up a 
significant portion of the charcoal (benzene is an aromatic hydrocarbon 
.... if you combine lots of them together they become polycyclic). The 
chacoal is 'activated' by being heated to a very high temperature in 
order to drive off the water molecules. This complex substance will bind 
anything that is hydrated in its natural state. This includes iron, 
chelated iron, other cations and organic compounds. The binding occurs 
through ionic interactions, hydrogen bonding, and also through Van der 
Waals forces (though Im told covalent bonding is unlikely). Substances 
which are bound by these forces are in equilibrium and can return to the 
'free' state so that a saturated carbon filter should still selectively 
remove substances which bind more tightly to the charcoal matrix.
In practical terms what this means is that carbon filters should not be 
used in a plant tank which receives regular additions of micronutrients 
(if you want to maximize the effectiveness of your micronutrients). 
I have recently removed my carbon filter and have noticed an increase in 
plant growth, though this anecdotal evidence is hardly conclusive. One 
concern is that the load of organic compounds (such as urea etc) in the tank 
could increase to toxic levels, though with lots of plants and few fish 
in the typical plant tank this may not be a problem ... something to 
think about.

Dr. dave.


Brita type filter, hardness and alkalinity

by Shane <shane-at-sure.net>
Date: Thu, 14 Nov 1996
Newsgroup: rec.aquaria.freshwater.misc,alt.aquaria

Sparrow wrote:
> 
> I have one of these jug-type filters to filter drinking water. The
> water that comes out has much less alkalinity and a lower pH. Is it a
> good or bad idea to filter water through this for my tanks? (My tap
> water is very hard and has high alkalinity siro 450ppm hardness 300ppm
> alkalinity). I also boil some of the water for my changes, but the
> kettle is pretty furred up and when inverted over the bucket flakes of
> limescale get in. Are these harmful?
> Local hardware shops sell things to prevent this scaling in the
> kettle, they are tangles of a shiny metal, looking like swarf or a
> coarse wired brillo pad. Does anyone know what they are made of, how
> they work ie by puuting something into the water to soften or taking
> something out. Again does anyone have any thoughts about ramifications
> in the aquarium?
> <<<<<<<<<<<<<<<<<<Spug (Sparrow) London, UK.>>>>>>>>>>>>>>>>>>>>


WAST OF MONEY!

The britta filter is just charcoal and cotton, break one open and check
it out for your self, then figure out how muchthe filter costs and how
many gollons it cleans, then make your own. If you have an old tank
around and an old filter, you got it made. throw in a heater and you've
got a temperature match too.  Personally I use a hose in my tank with a
few squirts of novaqua, but then again I have 180gal freshwater and my
smallest fish is a 9" oscar. (probably not the best way since I live in
Los Angeles county CA, polution capitol of the universe, but I find that
pampered fish are more fragile) I had my light fixture catch on fire and
melt the top of my tank into the water (and trash my house) it melted my
cords to power head and melted all my filter tubes and blew up my heater
and I only lost one fish in the whole incident, and it took him 4 days
to die.  It's the only freshwater fish I've lost in about 4 years!

Shane  http://www.sure.net/~shane/


Carbon&Iron

by "Justin P. Healy" <jphealy-at-sysconn.com>
Date: Fri, 7 Mar 1997

I was told again and again that carbon would not absorb iron. My
father-in-law, a water-purification engineer told me carbon could not
absorb iron. This conflicted with the reality I had experienced so I did a
simple experiment.

Into a ten gallon tank of freshly carbon-filtered water I poured chelated
iron until I got a reading in excess of 3 ppm. Were talking purple. I
filtered the water through a freshly cleaned and loaded 350 gph carbon
filter. In no time at all the iron fell to unmeasurable levels. Since then
I have used gravel and peat in my filters.

The suggestion that it is the chelating element that makes carbon able to
adsorb iron would make both my father-in-law right and me right. 

Thanks for the information.
Justin in Savannah, where a waist is a terrible thing to mind.

Take the Carbon Challenge

by Jeff & Denise Dietsch <dietsch/voicenet.com>
Date: Thu, 26 Mar 1998

Hello all,
  Here is another one of the challenges to the conventional net wisdom of
"Do not use carbon in the plant tanks."

  OK  For the last 2 years I have not run carbon in my tank, abiding by the
generally accepted idea that Activated Carbon will remove trace elements or
should I say "things that plants need".  Now I have been hearing more and
more people challenging this idea.  So I did a little surfing.  Well
needless to say I can not come up with the right string to search for and
99.9% of the millions of related sites are commercial pages selling their
carbon filters.  Needless to say I do not trust the "Facts" on these sites.
 The few sites I did find that were somewhat trustworthy had some
interesting information.  
(http://hammock.ifas.ufl.edu/txt/fairs/1682)
"It will not remove dissolved metals such as iron, lead, manganese, and
copper or chlorides, nitrates, and fluorides. Small activated carbon units
can remove only small portions of hydrogen sulfide. "
Yet a little further down that page I read this:)
"Carbon filtration can remove more than 90% of cadmium, chromium, manganese,
mercury, silver, and tin."

(http://www.agric.gov.ab.ca/agdex/700/16d42.html)
"These filters do not remove hardness, ferrous (dissolved) iron, fluoride,
sodium, asbestos fibres or other inorganic minerals from the water."

  So needless to say I am still not sure.  So maybe someone else can shed
some light.  Does AC filter out trace elements or not.  Does it actually
effect the ETDA or something else causing instability in our fertilizers?
Does it's absorption of VOCs and DOCs remove something else that plants
use?  From what I am hearing carbon will not absorb the type of ions that
are most important to plant.  But maybe the assertion is actually based on
something other then trace elements.  
   Then there is the choice of "well it doesn't really do much good, but
maybe some bad, and to be safe I'll leave it out, and my fish are fine
anyway."  I mean I have never had fish as healthy as I do now with planted
banks, but.  Well since we tweak our tanks to the nth degree maybe the VOC
and DOC absorption that has always warranted AC use is still a valid idea=2E
Along with all the other nasties it removes like pesticides, HERBICIDES,
and a plethora of others it clarifies the water, and that is good for
lighting.  I know I would love to remove some of the tannins I have in my
tank:)  

So does anyone have any ideas here or sights I can go to to read more?  As
usual one reference says it removes copper and the other says no:)

Thanks,
Jeff
AGA

Jeff's Carbon Challenge

by "Roger S. Miller" <rgrmill/rt66.com>
Date: Fri, 27 Mar 1998
To: Aquatic-Plants/actwin.com

> Hello all,
>   Here is another one of the challenges to the conventional net wisdom of
> "Do not use carbon in the plant tanks."
>
>   OK  For the last 2 years I have not run carbon in my tank, abiding by the
> generally accepted idea that Activated Carbon will remove trace elements or
> should I say "things that plants need".

Several years ago I did some work on the remarkable waste reuse plant at
El Paso, Texas, where they treat municipal waste from part of the city to
drinking water standards and inject the treated waste into the ground for
storage and later (years later) use.

That plant uses a multi-step system where, in a two-stage sequence,
powdered activated carbon (PAC) was used in dense suspensions with
clarified waste water.  It also uses a granular activated carbon (GAC)
filter as the last stage of processing.  The PAC acts primarily as a
foundation to support a very high bacterial population and probably also
serves to attach organic compounds and accelerate their breakdown by the
bacteria.  The PAC supply is continuously cycled from the reactor to a
regeneration facility that processes it at 400 degrees F and 800 psi -
really, not very much like filling a canister with chunks of carbon and
running water through it for weeks or months without replacement.

In that design, the PAC was intended as the primary treatment for color,
taste, odor, organic nitrogen (through nitrification and denitrification)
and three inorganics:  hexavalent chromium, metalic mercury and selenium.

The plant's operations are monitored so that we can tell how each stage of
the process effects different important pollutants.  I have some of the
early monitoring data.  The PAC process is very effective at removing
chloroform, carbon disulfide, mercury, and phenols.  It also lowers the
concentrations of copper, lead, zinc and strontium, but in each of these
cases, the PAC provided only a secondary effect.  The PAC had no effect on
xylene, toluene (which was pulled out before it reached the PAC) or
vanadium.  The primary effect on dissolved phosphorus and metals was from
lime treatment following the PAC stages.

The GAC filter (more-or-less like the activated carbon filters we're
more familiar with) was at the end of the process and only had a
measurable effect on zinc, and I think that might have been a fluke.

I don't know if EDTA chelates would be effected by activated carbon or
not.  My experience using chelated iron in tanks with activated carbon
suggests that it isn't adsorbed by the carbon.

>From this info and my past experience I think that very clean, fresh
activated carbon might attach some important plant nutrients, and that
characteristic might even last for a few days after its initial use.  But
under most common conditions it probably will not have a significant
effect.  It does attach organic molecules that cause color and odor and it
does serve as a very good base for biological filtration.  The bacteria,
in fact, can feed off the attached organic molecules and keep the carbon
in a partially active state for extended periods of time.

>
> So does anyone have any ideas here or sights I can go to to read more?  As
> usual one reference says it removes copper and the other says no:)
>

Activated carbon is commonly used for water treatment at both ends of
municipal and industrial water systems.  Environmental engineering
journals at your local library probably would be your best source of
information.


Roger Miller

   

Activated Carbon

by eworobe/cc.UManitoba.CA
Date: Fri, 27 Mar 1998
To: Aquatic-Plants/actwin.com

I talked to a chemist at the local university and he explained that
activated carbon binds ORGANIC carbon. Since the chelator EDTA is an
organic carbon molecule, it will be absorbed by the carbon filter. This
may also remove chelated metals from solution.

dave.

Carbon properties

by Luca Specchio <luckyluca/mclink.it>
Date: Wed, 05 Aug 1998

Dear Steve Pushak,

Upon contact with water containing soluble organic materials, granular
activated carbon selectively removes these materials by
adsorption. Adsorption is the phenomenon whereby molecules adhere to a
surface with which they come into contact, due to
forces of attraction at the surface. The use of surface energy to attract
and hold molecules is physical adsorption.

Adsorption is said to occur in three basic steps. These are film diffusion,
pore diffusion, and adhesion to the solute molecules to the
carbon surfaces. Film diffusion is the penetration of the solute molecule,
the adsorbate, through the carbon particle's "surface film".
Pore diffusion involves the migration of solute molecules through the
carbon pores to an adsorption site. Adhesion occurs when the
solute molecule adheres to the carbon pore surface.

The fact that activated carbon has an extremely large surface area per unit
weight makes it an extremely efficient adsorptive
material. The activation of carbon and its manufacture produces many pores
within the particles, and it is the vast areas of the walls
within these pores that accounts for most of the total surface area of the
carbon. In water, activated carbon has a preference for
large organic molecules and for substances which are nonpolar in nature.
The forces of attraction between the carbon and the
adsorbed molecules are greater the closer the molecules are in size to the
pores. The best adsorption takes place when the pores
are just large enough to admit the molecules.

Activated carbon, when contacted with water containing organic material,
will remove these compounds selectively by
a combination of adsorption of the less polar molecules, filtration of the
larger particles, and partial deposition of
colloidal material on the exterior surface of the activated carbon. The
extent of removal of soluble organics by
adsorption depends on the diffusion of the particle to the external surface
of the carbon and diffusion within the porous
adsorbent. For colloidal particles, internal diffusion is relatively
unimportant because of particle size. Organic
substances that pass through the column consist strongly of hydrophilic
organic molecules such as carbohydrates and
other highly oxygenated organic compounds.

Adsorption is partially the result of forces of attraction at the surface
of a particle that cause soluble organic materials
to adhere to the particle, and partially attributable to the limited water
solubility of many organic substances.
Activated carbon has a large and highly active surface area that results
from the activation process. This produces
numerous pores within the carbon particle and creates active sites on the
surface of the pores. 

Most of the commercial fertilizers contain chelated metals which are
ORGANIC compounds. These chelated metals will be binded to the carbon
pores, and as result their concentration into the water column will get
lower. As chelated compounds in aquariums slowly decade and free their
metals, the concentration of metals ions in the water will decrease
progressively too. In this way all the trace elements will be slowly but
constantly removed from thr water (if you don't add any!).

Sincerely,
Luca Specchio


Activated Carbon and Planted Tanks

by "John Godbey" <godbey/wizard.net>
Date: Thu, 6 Apr 2000

Peter Bradley wrote:
- -----snip-------
" What are other peoples experiences with carbon as a filter medium"

I had not used carbon since I first began growing plants in my tanks.  After
I read Diana Walstad's book I decided to give it a try.  My thought was
(after reading her comments) that I fed my plants every day, so even if the
carbon removed things the plants needed, they would be added back within a
day.

I can say with certainty after two months that the carbon has not harmed the
plants.  They look as good as ever; and they grow as fast as ever.  And
algae on the glass has gone from being an irritant that had to be cleaned
every week, to a minor problem that I work on every two weeks or so.
However, at the same time I began using carbon I also rduced my lighting
from 12 hours to 11 hours a day; so I am not certain how much of the change
is due to lights, and how much if any is due to carbon.

John Godbey
Springfield, VA


Up to Chemistry <- The Krib
This page was last updated 30 July 2000