Eupraxsophy

It may not be the most glamorous pursuit, but ensuring proper sanitation for the 40% of global population that lacks it is one of the most important issues of our time

On August 14th his charitable institution, the Bill & Melinda Gates Foundation, announced the gold-, silver- and bronze-medal winners in its Reinvent The Toilet Challenge, which aims to bring safe, affordable and “sustainable” loos to the 40% of the world’s population who lack access to basic sanitation, thus preventing many of the 1.5m childhood deaths from diarrhoea that now occur each year.

The Challenge is nothing if not ambitious. It seeks a toilet that costs less than five cents per user per day to operate, that requires neither a supply of clean water nor sewerage infrastructure to take the waste away, and that will generate energy and recover salts, water and other nutrients. Remarkably, despite the challenge being little more than a year old, the award winners claim to be on track to achieve all of these goals.

In third place is a toilet designed by researchers at the University of Toronto. This treats urine and faeces separately, using a material freely available in many of the world’s poorest regions: sand. Urine is filtered through sand, and the resulting liquor is exposed to ultraviolet light to sterilise it. Faeces are dried slowly within the toilet before being fed into a smouldering sand-filled reactor. The system can sanitise the waste of ten people in two hours, leaving only sand and fresh(ish) water behind.

The runner-up, from Loughborough University in Britain, brings chemical-engineering principles to bear. A tank feeds mixed urine and faeces through a rig that heats it to 200°C under high pressure, killing pathogens. Returning the superheated mixture suddenly to atmospheric pressure causes it to separate into its liquid and gaseous components. The gas is used to heat the feed tank. The liquid is fed into a digester that produces enough methane to power the entire system—and some to spare.

The winning toilet, however, is smarter still. It has been developed by Michael Hoffman of the California Institute of Technology, and has earned him the $100,000 first prize. Dr Hoffman’s toilet uses solar panels to power an electrochemical system that produces two things. One is hydrogen. The other is a compound which oxidises the salts in urine to generate chlorine. This creates a mildly disinfecting solution that can be used to flush the toilet. The hydrogen is suitable for cooking or for powering a fuel cell to produce electricity. The solid residue from the process can be employed as fertiliser.

The Gates Foundation will now pay for prototypes to be tested in the field, probably of all three winners and possibly of some other ideas, and Mr Gates hopes that the foundation’s reinvented toilets will start being deployed for real in as little as two years. They will thus be able to contribute to achieving what is the most off-track of the United Nations’ Millennium Development Goals, to halve by 2015 the proportion of people without sustainable access to basic sanitation. As the chairman of the UN Secretary-General’s Advisory Board on Water and Sanitation, the Prince of Orange, observes, “politicians and leaders worldwide don’t like to be associated with toilets, even state-of-the-art toilets. This sanitation stigma distorts international and national development agendas.”

Even something as “gross” to most people as toilets are easily taken for granted in their importance.