How Effective are Backflushing and Storage Practices for Squeeze Filters

Great report Ryan. Can you share the method you used to backflush the BeFree? I have not been backflushing mine because I was under the impression it would damage the filter. Although it seems like with your testing and performing an integrity check it should be fine. I’d like to come up with a method to do so without requiring me to bring a syringe with me.

Great article.  These kinds of filters have a lot of value in that they are small, light and relatively cheap for their function.  IMO, they should be treated as disposable items and replaced frequently.  Use them in relative clean water, carry chemical treatment as a backup and replace often (1-2 seasons, YMMV).  Why trust a filter with 5 seasons of use?  My 2 cents.

My compliments of this article. REAL data rather than marketing spin (as you mentioned).

Cheers

Is there a reliable DIY test to check the integrity of such a filter to ensure the sub-micron performance? I know you aren’t supposed to let one freeze, but there are other modes of failure.

Super-reliable? Probably not.
But if you measure the flow rate under gravity 9oe no squeeze), you may be able to see if there has been a sudden increase, which could mean a leak.

Cheers

Katadyn and Platypus both cite how to integrity check their filters. Sawyer does not but I imagine a similar test would work for it. Check their manuals but the tests are essentially to fully wet the filters then try to force air thru the filter. If air is able to pass through it implies a ruptured filter element. I don’t know if the direction really matters but Katadyn tells you to blow from the clean side thru the dirty side and Platypus tells you to squeeze air from the dirty bag thru to the clean side. The test is able to be done in the field.

DIY test for filter integrity?  There is an old phrase : “Slim and None, and Slim left town”.  You are taking about a 0.1 micron filter.

here is a blurb from Sawyer- The MINI filter removes 7 log (99.99999%) of all bacteria (like salmonella) as well as other harmful bacteria which causes cholera and E. coli and 6 log (99.9999%) of all protozoa such as giardia and cryptosporidium. These removal rates equal or exceed other filter options. EPA guidelines allow ten times more protozoa left in the water than Sawyer MINI filters allow. The MINI also filters out 100% of microplastics.

I think Zack is right if you are looking for a ‘large’ rupture.
I think Jon is right about the chances of pushing air thru an intact filter.

Cheers

Sawyer recommends using a mild chlorine bleach solution to sanitize for storage; you recommend Aqua Mira. Sawyer suggest vinegar to help remove calcification; you suggest citric acid. I’m curious how and why you came to the conclusion that your methods are better. Thanks.

I have some tests that reveal damage to the filter membranes in the presence of bleach that didn’t occur with Aquamira. Nothing major, but it’s noticeable on micrographs and I imagine it’s going to decrease filter life.

I used to use vinegar in my Sawyer, but then started seeing some weird gunk come out of my filter, so I tore it apart and it looked like the vinegar might have been dissolving the glues in there? So I switched to citric acid. YMMV, and that didn’t happen again. I didn’t spend much time investigating that, so don’t know exactly what happened or why it happened w/vinegar and not citric acid.

Also, in principle: chlorine dioxide can penetrate a biofilm polysaccharide matrix and dissolve that matrix more effectively than chlorine bleach. Bleach tends to oxidize some of the matrix compounds on the outer layers of the biofilm, and bacteria down at the surface remain protected. This is a well-known mechanism of biofilm protection in the presence of bleach.

Terrific article,  and for me at least, one of the most useful in recent memory.  I also see the error in my ways of not performing proper post trip maintenance on my filters.  Thank you.

good article, thanks

one thing mentioned previously is that if you have hard water, and add chlorine, and leave that in your filter, it can form calcium deposits.  So, in an attempt to prevent biological growth, you can clog the filter from calcium deposits.  Maybe leave the bleach solution in the filter for a while, then rinse out with clear water.

and, people use CLR to clear calcium deposits.  Some acid mixture.

Ok, so I had to come back and report on my results. I have a BeFree that I’ve used minimally for three seasons.  If I’ve filtered 50 liters I’d be shocked. After wetting, the flow rate was very low and I worried about bursting the bag from the pressure I was exerting.  Not having any citric acid, I mixed a 50% solution of white vinegar and swirled for 5 minutes.  Then, I used spa chlorine, which is neither hypo nor chlorine dioxide but it’s what I had available.  Swish and swirl for 5 minutes.  Rinse with clean water and backflush with my Sawyer plunger prior to connecting the 0.9 liter bag that came with the BeFree.  Let’s just say I was astounded by the results! I effortlessly emptied the 0.9 liter bag in well under a minute. Obviously,  I went off label and your milage may vary, but this technique resurrected a filter that I was going to throw out.

FWIW, after a trip, I flush my BeFree with a weak bleach solution and let it dry before storing. Before the next trip, the filter is usually clogged and I routinely soak it in vinegar and then give it a vinegar flush, which restores it to like-new functionality, as far as I can tell.

Can you give us an example of the citric acid that you used? I’m assuming you don’t mean running orange juice through the filter. Do you mean something like a lemon juice used in cooking?

Sawyer suggest vinegar to help remove calcification

Yeah happened to me after storing.  The water simply wouldn’t move.  Luckily there was a large convenience store at the start of my hike selling white vinegar.    Swished the filter and vinegar in a plastic bag, let set, and repeated with “fresh” vinegar until it water flowed again.

Excellent data and advice Ryan.
After flushing the filter with citric acid (or vinegar) and then chlorine dioxide, would it be best to flush it with deionized (DI) water before drying it for storage? I live in the mountain west and the tap water here is very hard (a lot of minerals). I’m just wondering if you have any idea how much calcification could occur from the one final flush being tap water and drying, compared to repeated use and drying in the field – is using DI water as the final rinse worth it?

Also, here’s another tip for readers: I’ve noticed that after storage, I really need to soak my filter and push clean water through it, to wet out the fibers, before it has much of any flow rate. I put a piece of tape over the inlet of my filter to remind me to do this at home where it’s much easier to get a container of clean water than in the field (especially if my dry filter is barely working to make clean water!)

Great article! I enjoyed the thought and work put into it. I’ll echo the questions of others above:

• What is the “5% citric acid solution” you used? Are you making it from a citric acid powder or sour salt?
• How do you backflush a Be Free filter? When I tried backflushing mine, the head flew off!

nm

I use a fine-grained, pure, anhydrous citric acid powder. We used it in our water softener. Can’t recall the brand, but it was cheap, and I think I bought it from some big online retailer.

Yes, I see that I forgot to describe the DI flush after the disinfection step. We have hard water where we live as well, and storing it after a DI flush is part of my process.

Backflushing a Befree: same process as the Quickdraw, just use a platypus softbottle and squeeze water back through the filter from the clean to the dirty end. I carry a flat foam donut gasket with me (hardware store) to help seal the platypus bottle neck to the filter around the spout, which gives me a good enough seal to exert a little more pressure.

This article is incredibly informative and helpful. Thank you for putting in the hard work to write this.

On the PCT I used these small 1 micron socks that slipped over the BeFree filter housing and did a great job of protecting silt clogging of the tubes. You could also slip them off and rinse in a stream or whatever clean water source

Purchased on Amazon for 6 bucks

http://DualPacks 1.0 Micron Sediment Pre-Filter Compatible with Katadyn BeFree, Made https://www.amazon.com/dp/B08HBQ7TW9/ref=cm_sw_r_cp_api_glt_fabc_F7ZE2E3AJ8Y5YQ68WZNA

Very good article, thank you for the good research. Look forward to trying it next season.
I do have a question, why double strength Aquamira? Aquamira is designed to kill pathogens in 2-4 hours at regular dilution and if it can damage fibers why increase concentration? With some chemicals increasing concentration doesn’t always increase effectiveness. I also assume Katadyn Micropur could be used instead of Aquamira.