Once upon a time when I was a much younger man I used to want to build a giant robotic killer whale (or a fleet of them) that would eat the garbage of the ocean.
One idea was having an incinerator in the stomach and blow the smoke out of the blow hole, but that would also be pollution... Then I thought about trying to use the waste as fuel... If not, there was another back up idea for a filtering process //then once it's full it goes to a designated place to dump the garage... And some of it will just most likely make it's way back into the ocean.