There's a reason that the industry standard for proper disposal of storage media, including HDDs, is nothing short of physical destruction.
It doesn't matter if the data is encrypted or not, the point of the matter is the data is still there when presumably that data should not exist outside <X> premises. Encryption serves as a mitigation against theft or accidental leakage of data, its purpose is not to facilitate data disposal.
Put another way, you have to answer Yes to this question for liability purposes: "Is the data gone?" The only way to say Yes with reasonable certainty is physically destroying the storage medium the data resides on.
Well, if you write 1 to every bit of the drive, and then write 0 to every bit of the drive, the data is gone… but to be fair, I think the concern is proving that actually occurred before disposal. It’s easy to see the data destroyed when the drive is ground up before your eyes.
It doesn't matter if the data is encrypted or not, the point of the matter is the data is still there when presumably that data should not exist outside <X> premises. Encryption serves as a mitigation against theft or accidental leakage of data, its purpose is not to facilitate data disposal.
Put another way, you have to answer Yes to this question for liability purposes: "Is the data gone?" The only way to say Yes with reasonable certainty is physically destroying the storage medium the data resides on.