Sometimes, an answer to a technological conundrum is there, quite literally, under our noses. Take toilet flushes for example. For those involved in water conservation, toilets are a headache. Even specialised ‘low-flow’ flush hardware can use 1.6 gpf (gallons per flush) – that’s approaching 6.1 litres. [Reference leglislation see : 42 U.S.C. § 6295 : US Code - Section 6295: Energy Conservation Standards] But a research team from the Institut für Abwasserwirtschaft und Gewässerschutz, at the Technical University Hamburg-Harburg, Germany, may have found a solution – following the realization that nearly all toilets have access to a readily accessible source of ‘free’ water which might be used for flushing. They are investigating the possibilities offered by so-called ‘yellow water’ (a.k.a. urine). Unfortunately, ‘yellow water’ has two appreciable drawbacks,  it’s yellow, and , it smells awful.
“… the utilization of yellow water as toilet flush liquid seems to be advantageous. To be accepted for this purpose, urine has to be decolorized (and also deodorized).”
Thus Dr. Holger Gulyas and colleagues at the institute set about evaluating possible decolorizing and deodorizing methods – specifically investigating whether combinations of ozone, UV light and H2O2 might do the job. Results of the tests, which could be described as promising, were published in Water Science and Technology : a Journal of the International Association on Water Pollution Research [2004, 49(4):241-246] see: ‘Screening of chemical oxidation processes and other methods for decolorization of urine for its re-use as toilet-flush liquid in ecological sanitation systems.’
Further reading – authored by Dr. Sunita Narain. who is Director General of the Centre for Science and Environment, New Delhi, India. ‘The flush toilet is ecologically mindless’ [from which the charming illustration above is taken].
Also See – ‘Urine Blindness’ (Waste Manag. Res., June 2013, vol. 31, no. 6, pp. 648-654)