I know that when police in my area need to destroy evidence that’s no longer needed (and can’t just be disposed of in normal waste streams, or sold or what have you) they normally take it to a local garbage incineration plant.

There was also a steel mill in the area at one point and their furnace was occasionally been put to use for similar purposes (tangential - there was at least one instance I’ve heard of where the US mint used that furnace to dispose of a batch of coins they were testing a new alloy or process or something on)