Obviously something's wrong here. Unfortunately the appearance has a lot to do with the developing process, and once developed can't be fixed. With traditional hand developing of B&W film, there are a lot of ways grain can be affected but there can be tradeoffs with sharpness. The type of developer, temperature and agitation can affect grain.

Very odd that all of the films look similar. What were the films? Delta 100 should be very clean from what I've heard although I haven't used it myself.

If you're going to scan them, I've found that it's best to scan the negative as a color transparency (slide) and then do the inversion and convert to B&W (using one of a few different methods) in Photoshop. Grain looks a lot better this way instead of scanning as a B&W film.