FWIW, I took a pair of biowheels out of the attic where they had been dry for 9 months and put them on a new tank to fishless cycle. The tank was used but had been dry for a loong time and I had cleaned with bleach. I filled it with freshly dechlorinated water, added a new heater, the old dry Penguin 330 with no cartridges, just the biowheel and a used thermometer and Seachem ammonia alert tag.
The wheels had been used for a few months and put up after just being swished off, not sterilized or anything, so they were sort of brownish and used looking. They had been in the attic for 9 months.
I added 4 tablespoons of ammonia to a 55 gallon tank, enough to put the Seachem ammonia tag well into the danger catagory (I think that got me to something like 6ppm based on later calculations when I had a new ammonia test). In something like 5 days the ammonia was nearly gone, I had to bring the tank inside and so I couldn't wait to see how long the whole cycle took.
So, I'll admit it wasn't a really well supervised test, I was actually mostly testing the new heater and figured I try to jump start cycling the tank with ammonia to get the biowheels going again and to see if they were at all useful after being dry so long. But, the results were pretty amazing to me. It would be interesting to have someone do this test more carefully, with better testing along the way.
But the result I saw makes me say that the bacteria can be revived even after long periods. Now, I have captured some mulm from the pond filter and dried it out, maybe someone would like to try to use it to seed a new tank? It might be interesting to see if it could help.
