If your printer is a Marco printer, the used toner needs to be returned to Marco. Here is a link with instructions: https://help.marconet.com/recycle-your-toner
If the printer is not a Marco printer, the toner cartridge can be taken to the Rolla Recycling Center on Old St. James Road during regular office hours. There is not a bin outside for these, you will need to go to the office and they will show you where to place the used cartridges.