Two new filter media are available that show promise in reducing costs and environmental impact.
The first is
called cellulose. Chew on a piece of wood and it will break down
into a mass of fibrous material. This jumble of fibers is
cellulose, a carbohydrate made from glucose, which is a form of
sugar. Paper is made from cellulose. Filters made from cellulose
paper have been in use hundreds of years. Now there’s a
cellulose media that can be used in an aquatic application as a
replacement for diatomaceous earth, which can be an environmental
You see, DE
is composed of tiny exoskeletons left by sea creatures called
diatoms. The collection of skeletons contains a microscopic
labyrinth that results in excellent particle filtration. However,
those same properties can be dangerous to humans.
Environmental Protection Agency considers DE a carcinogen and
recommends wearing breathing protection when handling it. Also,
California now requires that DE be disposed of at hazardous
cellulose is nontoxic and biodegradable when backflushed. That
means it can be thrown out with the garbage or disposed of through
the sewage treatment plant.
product has even gained National Sanitation Foundation approval,
thanks to a test that put the cellulose media in head-to-head
testing against various DE media. The results of these tests
(NSF Job PSF J-00014263) show that the cellulose media
performed as good or better than DE in terms of filtration and
pressure drop performance. If the tests prove true, cellulose is
capable of higher dirt loading, which means longer periods between
required filter reconditioning, less expense for new media and less
time to recharge.
Just keep in
mind that each cellulose brand is different when it comes to fiber
size and treatment. To prove they are capable of meeting NSF
requirements, all brands should submit to the same qualifying
tests. In time, I am sure that there will be other brands of
cellulose with the NSF label. The good news is that the “jury
is in” and cellulose is a bona fide DE
But the jury
is still out on another type of potentially
environmentally-friendly filter media: recycled glass, which can be
used as an alternative to sand.
glass from bottles or plate glass is crushed, classified and resold
as filter media by numerous companies. These products do not
currently bear an NSF certification, though.
is that the recycled glass possesses a weak surface charge that
helps to hold fine particles. But these weak electrostatic charges
are not a unique property of recycled glass. Electrostatic charges,
a phenomenon known as adsorption, play a role in all sand
recycled glass may have an advantage over sand is in its size.
Because glass has more interstitial spacing than sand, water goes
through it more slowly and thus can deposit more solid
also claim that recycled glass gives up its dirt easier than
conventional sand and thus backwash flow water volume is reduced.
If this is true, then money is saved in the form of less
wastewater. I would like to see a controlled set of data to verify
this because backwashing is sensitive to the type of dirt collected
and can be very subjective (that is, it depends on the clarity one
feels comfortable with in the backwash water
have heard the claim that the smooth surface of recycled glass
keeps it almost free from bacteria, while sand can become loaded
with bacteria. However, I have been in a lot of pressure filters
during various stages of their lives, and I have yet to see a
problem with bio film. Proper disinfection kills bacteria
throughout the pool system, including inside the filter.
Disinfectants such as chlorine act not only to kill bacteria and
destroy bio film, but also to oxidize residue.
As you can
surmise, more study is needed to determine whether recycled glass
filtration media lives up to its claims.
Wolfram Hartwig contributed technical information to this column.