There isn't a single thing in the Bible that indicates that the world is flat. The Bible is NOT a science text, and was not written with such a purpose in mind, therefore there's no point using it for such a purpose.

All mariners knew the world was round long before Columbus ever sailed. You can see the curvature of the Earth at sea on a relatively calm day, and you can see the masts of a distant ship before you see its hull loom above the horizon, which again indicates the curvature of the Earth. Greeks, Romans, and Egyptians knew the Earth was round. So did sailors and moderately educated people in medieval times, but I don't doubt that some poorly educated landbound people may have thought the Earth was flat...if they ever thought about it at all. They probably did not.