I have excess cellulose / blown-in insulation. Can I compost that in my backyard, as it is essentially wood? I do not plan on using it for composting with plants that produce vegetables or fruit.
While I could repurpose it, I prefer working with rigid foam, fiberglass, on the expanding foam.
The cellulose is at least 15 years old. Would it have been common place for it to be treated with chemicals then render it unsafe for composting?
Maybe! Sorry it's not a more definite answer.
While you can compost it, it will be treated with a fire retardant of some sort. That might be borax, boric acid, and/or ammonium sulfate, all of which are relatively OK to have out in the environment.
What is more worrisome is the fact that it might be made from recycled newsprint or other printed materials. The inks used could have all sorts of chemicals in them such as heavy metals. Putting those out in the environment isn't the best idea.
As a result the best practical uses are reuse if it's still in good condition, or sanitary landfill if it is not.
Way more details are available at this NIH study if you happen to have insomnia.
Cellulose is treated for fire resistance (and possibly against mold). It'll break down for sure, but it'll leave chemicals behind. I'd put it on your local marketplace for cheap and recover some value.
The "acid test" is probably to try incinerating a small amount of it. If it burns easily, it should decompose under the right conditions.
If not, then you know it has been heavily treated, and should either go to landfill or to a high-temp incinerator if possible.
