The No-Mix Vacuum Toilet, conceived by the Nanyang Technological University in Singapore separates the brown from the yellow on-site to conserve water and make use of energy-rich resources.
More than one gallon of water is used to flush waste down the bowl when only 0.05 is needed for urine and 0.26 for feces. This means that the system in place now is extremely inefficient. By flushing according to the waste laid, water is used sparingly while the nutrients in urine can be more easily accessed to add to fertilizers and feces can be used to power electricity. Otherwise, treating mixed waste is extremely difficult.
The design has been adopted by a few countries in Europe, but it will be a long while before any toilet of the sort becomes mainstream.