Introduction

Some of the things we love about the Seitz Supradisc II® lenticular filters by Pall are that they are back flushable, hot water- and steam-sanitizable, and storable between uses. This mean you can use them over and over again without the media warping, until they are full of solids or when a regeneration procedure doesn’t bring the differential pressure back down.

In this excerpt we will discuss the solutions for storing your modules correctly between uses to ensure longer lifespan and higher total throughput. They are easily stored in a liquid solution and shouldn’t be allowed to dry out as this will cause turbulence during a filtration and premature fouling or bypass.

Storage Under Pressure

One option is to store your modules under pressure inside the housing. Pall recommends steaming or hot water sanitizing them after a regeneration (backflush followed by forward flush procedure), and then placing the module in the drained housing under at least 1 bar (14.5psi) and up to 1.5 bars of pressure with a food grade gas like nitrogen. You can also use CO2, but take into account that CO2 is a soluble gas and it will take longer to build up the proper pressure. As long as the pressure does not drop below 1 bar, the media can be stored like this for months. This only works if your seals are sound so that pressure cannot escape over time. Keep in mind that many housings are not pressure rated for gas pressure, only liquid pressure, so for safety’s sake don’t pressurize a housing without that certification in hand.

Storage in Solution

The most common storage method is to store the modules in a storage solution in the housing, or in a suitable container with a lid where they can be weighed down to keep them fully submerged. For storage in a solution for longer than two days we recommend removing the silicone gaskets or O-rings on the modules, otherwise they will stretch, become brittle and break up into little pieces. A brew fermentation bucket that is not tapered is suitable for the 12” modules whereas food grade plastic trash cans or Rubbermaid totes with lids are suitable for the 16” modules.

Please note: When storing media in a liquid solution, make sure the media is either purged with nitrogen (see lenticular operating instructions) or recirculate the solution through the media before removing it and storing in the same or fresh solution. The 16” media, in particular, has a large amount of surface area (5m2) and placing a wet, unpurged module in a storage solution can dilute the storage solution to the point where it won’t sufficiently protect the media over time.

Here are a few solutions to store your modules in:

Inexpensive ethanol (vodka)

(neutral, not denatured-, isopropyl alcohol or methylated spirits) Make sure you that the strength is at least 40 proof but not higher than 135 proof at which point you can start to prematurely age and crack the module cage or storage container over time. This storage solution is good for weeks to months.

When choosing this method be aware that your module should be purged with gas before storage to ensure that little to no dilution of the alcohol takes place. Remember to bring the backpressure up to 3 - 5 psi when purging to force the gas into all the pores to get the most of the liquid out.

If the alcohol % of the vodka is under 20%, you will likely see spoilage organisms start to grow inside the module. Therefore, we only recommend this method for 12” modules. 16” modules have a lot of internal surface area and requires impractical quantities of alcohol. We also see poor distribution of the alcohol within the depth of a 16” module which inevitably leads to spoilage.

Acid Sanitizers like nitric or phosphoric acid blends

The manufacturers of cellulose filter media advise against using phosphoric acid or nitric acid solutions or long term contact with oxidizing sanitizers like peracetic acid. These acids tend to break down the resin that binds the cellulose media together and that can lead to a premature breakdown of the cellulose structure which in turn can lead to the filter media landing up in your filtered product as well as inconsistent filtrate quality. Running these chemicals through the media just before filtration is acceptable but contact time longer than recommended, is detrimental to the media. Some of them can also break down over time, change colorand cause off flavors in the media at which point bacteria can easily start to grow again.

Storage under pressure

You can store your cartridges inside the housing between uses. After a hot water or wet steam sanitization, drain the housing, close it up and place under nitrogen or CO2 pressure. Don’t let the media dry out before placing under pressure. Maintain a pressure of between 1-1.5 bar. This is also a good way to tell whether all your gaskets are sound. We prefer an insoluble food grade gas like nitrogen. You can also use CO2 but maintaining pressure will take longer since it’s soluble and much of it will dissolve in the water left in the cartridge before pressure starts building up. Please take proper safety precautions as most cartridge housings are only pressure rated for liquid pressure, not gas pressure. Removing the O-rings aren’t necessary for this method. Cartridges can successfully be stored this way for months as long as the pressure doesn’t drop below 1 bar. If it does, re-wet the media, sanitize, drain and store.

Other Acids

Acceptable acids to store media in include citric and tartaric acid but for the long term it has to be used in combination with potassiummetabisulfite (KMBS) to keep spoilage organisms from metabolizing these bio-essential acids over time. This method is commonly used in the wine industry and modules are stored this way in the long term. Periodic additions of SO2 has to be maintained to keep the modules from spoiling.

Sulfuric Acid:

A 2% sulfuric acid solution is acceptable for a 6+ week time storage solution with no detrimental effect to the structure of the cellulose media over time according to the manufacturer.

Solutions to avoid:

Definitely not recommended, not even at your own risk is Ozone which will destroy the media within minutes, as well as Iodophor, which will permanently stain the media. Caustic soda is also not recommended for contact of more than 6 cumulative hours, as it is difficult to remove/neutralize and will also start to break down the cellulose structure after this time.

Whatever storage solution you choose, make sure that you regularly inspect the solution to make sure that your modules are properly submerged, that the gaskets have been removed, and that your solution is still sanitary.

LENTICULAR MODULE STORAGE SOLUTION OPTIONS

Storage Solution
Contact Time
Notes
Inexpensive ethanol (vodka)
Months
  • Keep strength above 20%/40proof but under 67.5%/135 proof.
  • Do not use denatured spirits.
  • Not recommended for 16" modules, only 12"
  • Purge out water very well before submerging to avoid lowering proof < 40 degrees.
Nitric and Phosphoric acid/blends
Max 6 hours cumulative
Use at own risk. These acids damage the cellulose structure at longer contact times.
Peracetic acid at 0.05%
≤ 3days
After this time the peroxide in the formulation will have broken down, offering little protection against spoilage. Storage at a higher concentration can lead to premature breakdown/damage of the media.
Citric acid 1-2% solution
≤ 3days
After this time bacteria will target this solution. Commonly used in wineries with 50-200ppm of added SO2 for long term storage. Periodically add more SO2 by dropping in an Inodose effervescent tablet. Care should be taken if bacteria is already present in the cartridge, then bacterial spoilage will begin within hours without added SO2.
Caustic soda (NaOH or KOH 1-2%)
≤ 6 hours
Difficult to neutralize, longer contact time weakens cellulose structure
Ozone water/gas
Not recommended by manufacturer
Instant destruction of media
Iodophor or other Iodine based sanitizers
Not recommended by manufacturer
Permanent staining of media