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 hazard.
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.
Indeed, the 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 material landfills.
In contrast, 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.
One new 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 substitute.
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.
Recycled 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.
Another claim 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 filtration.
One place 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 contaminants.
Manufacturers 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 stream).
Finally, I 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.
