| The following questions and
answers are not intended to make you an expert, but rather
to give you some insight of what activated carbon is, what
it will do and what it will not do.
Q: What is activated carbon?
A: Simply stated, activated carbon is carbon which
has been either steam cleaned or chemically cleaned to open
up the pores which has been exist within the
structure. It can be produced from a wide variety of
materials, such as peat, coal, wood or even coconut
shells. The base material affects the performance
characteristics of the final activated carbon product.
Q: How does it work?
A: Activated carbon "removes"
contaminants through two (2) different processes, adsorption
and chemisorption. Although these processes differ
slightly in the way they work, the basic idea is that the
contaminants being removed stick to the surface of the
carbon. Obviously then, the greater the surface area
available, the more things can be removed. Due to the
large amount of pores existing in activated carbon, the
available surface area can be as much as 150 acres per
pound.
Q: Can activated carbon remove
chlorine?
A: YES and NO. Chlorine taste removal is one of
the most popular applications for activated carbon.
Activated carbon does not actually remove the chlorine, but
causes it to change into a form that does not impart an
objectionable taste and odor to water. Therefore, the
carbon removes the chlorine taste and odor, but does not
remove the chlorine as chlorine.
Q: How about organic contaminants?
A: Along with chlorine "removal", organic
is also a popular application. There are several
organic chemicals which can be removed with activated
carbon, as well as several factors which affect it's
performance in removing them. Tri-halomethanes (THM's)
are probably the most widely discussed removal application
in the drinking water industry, when organics are the
topic. The reason for this is that THM's can be formed
in chlorinated drinking water supplies and are known to be carcinogens.
NO activated carbon system should be sold on a non-potable
(unsafe) water supply without the proper per-sale testing
and performance safeguard procedures.
Q: Is bacteria a problem?
A: It can be. Activated carbon can provide an
ideal growing environment for some types of bacteria.
For this reason, activated carbon filters should not be used
where the water is microbiologically unsafe or with water of
unknown quality. Obviously, municipal supplies and
approved community and private wells are required by law to
be safe and thus in those applications installing an
activated carbon filter is usually a safe boat.
There have been attempts to make carbon
less susceptible to bacteria growth by impregnating it with
silver. The EPA reports the silver to be a marginal
bacteriostatic agent. It's life span is limited due to
leaching silver into the water, usually to levels below the
50 parts per billion limit.
Q: Can activated carbon remove
everything?
A: NO! As in all water treatment devices, there
are limitations. Just to name a few, the following are
taste and odor situations:
- Activated carbon will not remove salty
tastes due to chlorides.
- It has very limited capabilities in the removal of
hydrogen sulfide gas (rotten egg smell).
- Certain organics, such as methanes, are very poorly
removed.
- Activated carbon can remove some sediment, but since this
can plug the pores which are vital to it's performance, it
is not recommended for this
purpose.
Q: What is carbon capacity?
A: There is no definitive answer
to this question, since there are several different factors
which can affect it's capacity. Carbon's capacity will
vary depending not only on the material being removed, but
also upon the other contaminants in the water as well.
It's capacity is also dependent upon the pH and temperature
of the water. Turbidity in the water, which plugs the
pores in the carbon, will even fluctuate on a given
application, thus there is no way to give an absolute answer
to this question. You must replace the carbon when it
no longer removes what was installed to remove.
Water treatment
using activated carbon can be a vast and sometimes
complicated proposition. Obviously, this brief
question and answer bulletin cannot provide you with
information about all it's applications and
limitations. The intent is to simply give additional
knowledge to make you feel more confident in selling
activated carbon systems. |
