One of the first principles of process engineering is segregation (or separation of waste streams). The effluent from one process can be the influent for another. In many developed societies, we aggregate our poo & our wee with vast quantities of water, transfer the slurry over vast distances, only to separate the components out again using energy intensive physical, chemical & biological processes.
Physiologically, are poo & our wee are separated. We need to design our user interfaces (toilets) with baffles or separate urinals to enable the collection of urine.
Urine can be a precursor or feedstock for many useful industrial chemicals including fertilizers, sodium hypochlorite (bleach).