Today sewage system when we flush it will mix everything with potable water and then send them to treatment plants for energy-intensive and expensive treatment to break down organic wastes, separate out biosolids, kill pathogens, and release the water into rivers or aquifers. In this system we have missed out a great opportunity to collect the valuable urine before it is mixed with poop and flushed away.
According to Alex Wilson when most people think of creating fertilizer from animal or human waste, we think mostly about manure. But there are actually far more nutrients contains in urine than in the poop. In human waste, 88% of nitrogen and 66% of phosphorous contain in urine. Therefore, it makes more sense, less energy and cheaper of course, to collect the urine even before it mixes with the poop and flush water.
Urine is far more easier to deal with. Simply storing urine for a while in a sealed container is enough to kill bacteria, due to the high alkalinity and ammonia from the urine. So no expensive and energy-intensive treatment is ready needed to process urine.
Plants need phosphorus, and we are running out of the it. Some predicts that phosphorus production will peak by 2030 and then decline. Without recycling urine to recover the phosphorus soon we will run out of it and will create a tremendous negative impact to the ecosystem.