Introduction

Just like with our lenticular modules, cartridge filters should be stored wet between uses. Some prefilter cartridges can be backflushed. Some membranes cannot. You can still perform a forward flow regeneration to try and dissolve the soluble compounds in the matrix if you have a non-backflushable cartridge. Please check with Scott Labs, or refer to the product technical data sheet whether your cartridge is backflushable or not.

Regeneration

A forward flow regeneration is done by rinsing with water about twice the speed you were filtering at. Keep this high flow for 5 – 10 minutes and then bring the water temperature up to no higher than 140 ⁰F. At temperatures warmer than 140⁰F, proteins lodged deeper in the matrix start to denature where they will stay and contribute to pressure buildup.

After 5 minutes of warm temperature high flow, switch the pump off and close the valves so that your cartridge sits in this warm environment for 10-20 minutes. Then bring the temperature back down incrementally by rinsing with cold water. Drain and store or drain and reuse. Alternatively you can continue with a hot water or steam sanitization.

Some cartridge manufacturers also recommend soaking the cartridges in caustic solution (sodium or potassium hydroxide) followed by an acid to neutralize the high alkalinity. Take care to remove O-rings before soaking in extreme pH environments.

Storage

It is a good idea not to let your cartridges dry out when storing them so that the materials remain pliable. Otherwise they may become brittle and cause internal turbulence and premature damage during subsequent use. Typical storage solutions include:

Inexpensive ethanol (vodka)

(neutral, not denatured-, isopropyl alcohol or methylated spirits) Make sure you that the strength is at least 40 proof. This storage solution is good for months to years, as long as the concentration doesn’t drop below 40 proof/20% alcohol.

Acid Sanitizers

This solution is typically recommended where there is a very short time lapse (less than 3 days weekend) between filtrations. After this time, some acid sanitizers tend to break down (it becomes milky with a foul smell) and you won’t have protection from microorganisms. Acid based sanitizer solutionsor oxidising sanitizers are not recommended for long term storage.

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.

During storage in ethanol and acids, be sure to remove the O-rings between uses. Silicone tends to stretch and break up into little pieces when stored in these solutions long term. You can make your own storage containers to store the submerged cartridges in. Simply use plumbing water piping and cap one end to make it leak-proof. The storage solution filled tube can be capped or covered with plastic wrap. Stand the cartridges upright in these tubes and use a bungee cord to secure them to a barrel rack, wall or table. Make sure your cartridges are fully submerged in the storage solution. Alternatively, you can leave your cartridge/s in the housing with your chosen storage solution. For 10” cartridges you can store them in a zipped plastic bag in the storage solution of your choice.

Regardless, if you plan to store cartridges for longer periods in a storage solution, remember to remove the O-rings first.

CARTRIDGE FITER STORAGE SOLUTION OPTIONS

Storage Solution
Contact Time
Notes
Inexpensive ethanol (vodka)
Months
  • Keep strength above 20%/40proof.
  • Do not use denatured spirits.
  • 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 membrane 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 structure
Ozone water/gas
Not recommended by manufacturer
Instant destruction of media
Iodophor Sor other Iodine based sanitizers
Not recommended by manufacturer
Permanent staining of media