Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Making sure the pathogens in human waste are dead before anything is handled or spread, and that the nitrogen and phosphorus in it do not run into a watercourse. Time and temperature are what kill pathogens, so this need is mostly about waiting long enough in the right conditions.