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?
Urine and faeces, before any separation or treatment. A dry toilet takes them in, and composting turns them into a soil improver and plant feed instead of sewage.
It comes from the household itself: the people living in the house, and what they do there.