Reuse it until the orange colour turns green - then it has been oxidized to a less toxic form. Combining it with a sulfite clearing bath when doing traditional bleach and redevelop processes will speed this along.

Allowing it to dehydrate to a slurry will minimize the amount of hazardous waste you turn in. Mist wet any areas that have dreid entirely before you scrape/spatula the sludge into a small bottle - label it and turn it in to a HHW depot.