9 Things You Should Know About Your Compost Carbon Filters

This article is going to be so much fun!  Please be patient with me while I nerd out a little on this subject.  I know you are probably here because you have questions about your carbon filter but bear with me.  The more you know, the more you’ll appreciate this innocuous little filter. 

I’m going to start by saying I’m specifically discussing matt fiber carbon filters, the little disks we stuff into the lids of our composters or trash cans.  Carbon filters are commonly found in air purifiers, water purifiers, industrial applications, etc.  I’m going to narrow down scope to this tiny corner of the carbon filter world and focus on answering some questions and some of the answers might surprise you. 

What are activated charcoal/carbon filters?

Lets tackle what your carbon filter is and what it is meant to do.  Firstly, your activated carbon filter is not a particulate filter.  This means, it is not meant to filter dust, dander, mold spores or any other physical particles.  The carbon filter is special because it can trap gases, aka odors.  It does this by means of adsorption.  I’m not going to go full nerd here but I’ll break down the basics because once you understand the gist of how they work, it should answer some of your questions.

How does the carbon filter work?

Adsorption? Don’t you mean absorption?

Adsorption is where gas molecules stick to the surface of a solid.  The molecules aren’t being absorbed into the material, they are staying on the surface.  This is basically how activated carbon works.  Gas molecules (specifically VOCs and gases that cause common household odors) stick to the surface of the carbon particles.  So, the stinky gas molecules stick to surface of the carbon, they aren’t being converted into clean air or changing state.  They’re just trapped there. 

What is the difference between carbon and activated carbon?

Surface area.  The difference is that activated carbon has gone through physical or chemical processes to increase the surface area of the carbon particles.  Think about it this way:

If you were to take one particle of activated carbon and zoom in

And zoom in

And zoom in

The surface wouldn’t be smooth.  The surface would be riddled with tiny crevices, like a microscopic grand canyon of crevices.  This gives that one small particle of carbon a lot more surface area to park gas molecules.  This is what we refer to as activated carbon.  We’ve increased the available surface area to trap the gas molecules. 

So as more and more molecules stick to the surface of the carbon particles, all the parking spaces fill up and eventually odors start passing through the filter.  There’s just not anymore parking spots for the gas molecules.  When this happens, you’ve reached the end of your filter’s life. 

Are carbon filters washable?

So I just wash the filter then right?

Well…yes and no.

Some carbon filter disks are marketed as washable.  This means you can wash the filters per the manufacturer’s recommendations and it will remove any trapped particles, dirt, or mold without damaging the filter and removing the carbon.  However, washing the carbon filter wont remove the trapped gas.  So if you want to wash your carbon filter every once in a while to keep the mold from growing in your filter or food particles out of it, then yes.  It’s totally fine.  However, washing your filter won’t prolong the life of your filter or refurbish your filter.

Can I refurbish and reuse my filter?

Nope.  In theory, you would have to heat up the carbon particles with enough energy to release the gas particles.  You would have to bake the gases out of the filter and you would be releasing these gases back into your house.  On top of that, you’d damage the fibers that the carbon is impregnated into.  So short answer is a definitive and strong no.  Please don’t try to bake your filter clean. 

Can I compost my filter?

This was not an easy thing to figure out. 

When I was researching the filter material, it was beyond frustrating to try and track down the actual manufacturing process.  In a formal life, I was a materials engineer, so I knew enough to know that the ingredients list of just “activated carbon” was very unlikely.  You typically see that the carbon in activated carbon filters is either impregnated or somehow retained mechanically into a filter.  There are a lot of different iterations of carbon filters.  They all basically work the same way, however, the manufacturing process of how they are made is where you see some of the more noticeable differences. 

So what are those carbon filter disks that you stuff into your trash cans and composter bins?  Well they are most likely a polyester or nylon fiber that is impregnated with activated carbon.  The carbon really needs something to help keep it together and the fiber mats do a very good job of keeping the carbon in place and allowing for maximum surface area exposure.

So what does this mean?  Well it means that these filters are made of carbon (which is compostable) and a polyester or nylon (not compostable).  Polyesters and nylons are petroleum products and you don’t want them in your compost pile.  I’ve yet to see clear packaging for any of the brands I’ve reviewed that state they are compost safe.  I do believe that they are potentially recyclable, but you’ll need to check with you’re recycling center.  So DO NOT put your carbon filters in the compost pile. 

Honestly, it was surprisingly difficult to get a clear answer on this issue, but now that I know the filters aren’t compostable, it’s also a bit disappointing.  So, I’m composting kitchen scraps and being more environmentally conscientious but now I’m buying something that is disposable that has to go in the trash?  This led me to my next question:

Do I even need a filter?

Well…there isn’t a wrong answer here.  It really depends on whether you want to use a filter. 

If you want to go composter commando, you go for it!

You only need a filter if you’re fighting unfortunate smells.  If you empty your container daily into your backyard composter, then maybe you don’t feel like you need one.  If you wait several days or you participate in an urban composting program, I could see where having a stinky compost container in your apartment would be…unattractive. 

Keep in mind that the filter is not compostable and at absolute best it is a recyclable product, at worst it’s going to the landfill.  I hate giving bad news but it’s better that everyone knows the actual reality so we can make good choices for ourselves and our environment.

How long should a carbon filter last?

The life of your specific filter is dependent on a couple of things:  the quality of the filter and how much you utilize it.  If you have a good quality filter, this means it has more activated carbon than other filters.  Most manufacturers will give general lifecycle guidelines for their filters.  I’ve seen 4-6 months at the high end but 1-3 months at the low end.  This large span in expected lifecycle probably has to do with the quality of carbon and how much is impregnated into the filter.  Secondly, the more you use your composter, the longer you wait between cleaning out the composter, then the more gas that is produced and will be trapped in the filter, ultimately reducing it’s life.

How do I know when I need to change my filter?

Does your kitchen stink?  No, then your filter is probably fine.

What if I have mold in my filter?

Mold in your composter is normal and expected, however mold in your filter is not good.  As previously mentioned, your filter is not designed to contain mold spores and you don’t want mold spores being released all over your kitchen.  If you’re battling mold problems, then I encourage you to jump over and ready my article about mold in the kitchen composter. 

In conclusion, your run of the mill carbon filter disk is NOT just carbon and therefore NOT compostable.  It does have a lifecycle and when your composter starts to let the smells out, the filter is full and ready to be changed.  It goes into the recycling bin or trash, it cannot be refurbished and reused.  You can wash your filter to remove dirt, dust, mold spores and other particulates but washing will not remove the trapped gas.  If you decide you’re going to stick with using carbon filters, be sure to read the manufacturer’s information on whether the filters are recyclable and/or washable.  IF I find a filter that is home compost safe, I will absolutely shout it from the rooftop… or at least update this article. 

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