During space travel, what shall become of human waste?

Some fanciful process could convert excrement into a bio-sustaining compound like plant food, or something.

Lacking such a process, astro-mealtime-output would be jettisoned as a frozen cube into the deep black of space, destined to fall into some gravitational pull, perhaps illuminating a night sky like a falling star, to be wished upon by a small child.

IanM Idle Thoughts