The composting toilet separates liquid waste from solids. The solids are then composted (allegedly without odor). The compost needs to be removed after a while and can be used as ... compost. The liquids need to be dumped frequently - but apparently that is not a huge problem.
I have not had one or used one, but I have heard good things about them from people who do.
All of these concepts have their pros and cons. The black tank did not work well for us. We had to stop by the local dump station at the end of every trip, for one. But the good thing is that everyone gets to pick the solution they like best.