I have a couple myself that I need to get rid of so I did some looking. Easiest way would be tossing in the trash but that seems like a waste. I'm going to dump the carbon in my garden and the rest goes in the recycle bin the city I live in provides.
http://www.phreshfilter.com/page/phresh-frequently-asked-questions/
How do I dispose of the filter when its life is up?
Use the carbon in your outdoor garden soil. Take the steel and aluminum to a recycling center or metal scrap yard.
https://www.livingnaturaltoday.com/2016/09/natural-uses-for-activated-charcoal/
As a Garden Booster
By using activated charcoal in your garden you’ll be able to improve soil drainage, reduce the risk of soil compaction, and also boost the nutrient level of the soil. There’s more though: activated charcoal can also improve soil’s water retention abilities, which is great for gardens that don’t get watered on a daily basis.
Aside from the soil boosting effect, activated charcoal helps improve germination and can also boost your plants’ ability to resist fungal disease and insect infestations.
If you’ve been looking for a natural fertilizer and eco-friendly insecticide, then you just found it. All you need to do to take advantage of what activated charcoal can do for your garden is to mix activated charcoal powder on a 2:3 ratio with organic compost. Treat your garden with the mixture on a monthly basis and you’ll be reaping the tranquil, green rewards in no time at all.
It should be noted, you don’t need to use food grade charcoal as it’d get very expensive.
As you can see, there’s more to activated charcoal than just its
teeth whitening and bloat-busting abilities. We’ve just shown you 3 natural and safe ways to use activated charcoal in and around the house; all you need to do now is to start implementing these great ideas!