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Re: Jeff's Carbon Challenge

> 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

Roger Miller