You could re-scan the document, and save it as a .tif file. Then open it up in a photo editing program, like Photoshop. Convert the picture to 8-bit grayscale. Then use the brightness and contrast tools, to make the grey background white, without making the text washed out, or lose detail. You want to brighten just the upper range (light grey to white), without making the black text any brighter.
You may also have to use the gamma tool, which blackens the mid to low grey tones. A little experimentation is in order. After you've gotten the right look, you should save it as a .jpg file, then print that.