Got to be a better way!

Warning -- this is a rant!

I have been shredding old financial records. I do this every summer when I am the only person in the office. It is a nasty job, uses lots of time, and the shredded material takes up way more space than the documents did in their original form. Yes, I understand that for security reasons, old financial records need to be destroyed, but there has to be a better way. A small pile of mostly biodegradable paper is shredded and placed into trash bags which not only take up way more space than the unshredded documents, but it goes to the landfill preserved in plastic trash bags which last an infinitely long time. Isn't there some other secure way to destroy sensitive documents?