Hi. I am a chemist, and when we have to dispose of substances such as iodine (which believe it or not IS considered a hazardous waste in many jurisdictions), we have to dispose of it with our halogenated organic waste. Iodine is very reactive, and the heaviest (and only solid) halogen. Most areas have a day when they pick up hazadous materials, such as old batteries, etc. I would dispose of the iodine that way. Don’t just dump it, as I said, its very reactive. besides killing the bacteria by reacting with the polar ends of the cell membranes, it can also haloganate the septic tank.
Richard
chemist