|
Arsenic
Removal
Arsenic
is found in just about all ground water and exists as
either a tri (+3) or penta (+5) valent anion specie. It
is largely a naturally occurring contaminant. When the
EPA recently decreased the MCL from 50 ppb (parts per
billion) to 10 ppb, many wells once considered safe now
had to be treated. One of the most common treatment methods
for municipally supplied water is to first oxidize the
tri-valent arsenic to penta-valent with ozone or chlorine
and then use a co-coagulent such as ferric chloride or
an aluminum salt to co-precipitate the arsenic and filter
it out. Activated
alumina is also an effective media for arsenic removal
for use in pressure filters.
Of
the more recent media developments used for arsenic removal
are the granular ferric hydroxide and ferric oxides commonly
known as GFH and GFO and the hybrid ion exchange resins
that are treated with an active ferric functionality to
bind with arsenic, allowing easy removal. One such resin
is the ArsenXnp
from Purolite Company.
Systems
using ArsenXnp
are usually designed as a lead/lag configuration with
a monitoring port in between the two units. Although ion
exchange at heart, the ArsenXnp
resin is actually an adsorbant and there are several factors
to be considered making up a proper design. Check out
my article on this web site for more detail.
Arsenic
removal systems should be lead/lag with complete redundancy.
Municipal systems are often designed at 2 to 3 gpm/cu
ft of media for economic residence times while residential
units are often run up to 5 gpm/cu ft (with a recution
of capacity). Throughput capacities can range from 50,000
to 500,000 gallons per cu ft depending on the variable
and feed water composition. Municipal and larger systems
can be regenerated using a proprietary technique generally
done off site by a licensee. Disposal of the spent media
is generally as ordinary landfill but because of the high
adsorptive capacity per cu ft, spent media can be considered
as a haz waste by some states.
Strong
base anion resin using salt regeneration can also
be used for arsenic removal in residential systems. If
there is a need to use strong base anion for the removal
of other contaminant (ie uranium or nitrate), the process
can often be accomplished with a single resin in a single
tank. Check with us.
Systematix
also produces a series of specialty cartridges
(See our site listings for Aqualine™
Cartridges) that can be used alone as under-counter
filters, R/O polishers or in-lines.
|
