We can hard delete record or list of records using emptyRecycleBin() function in apex. Pass the record or record list to emptyRecycleBin() to delete it from Recycle Bin.
Contact con = new Contact(Id = '09k110000O5abc'); Database.emptyRecycleBin(con);
Note: The DML operation datatbase.emptyRecycleBin() is limited to 1000 items.