Hi-tech toilets save lives - and mean big business
In a world where 2.5 billion people still do not have access to basic sanitation facilities, and 1.5 million children die each year from preventable diseases as a result, there is a pressing need to find sustainable solutions to this most ancient of human problems.
But this isn't just a humanitarian issue - it is also about hard-headed economics.
"The United Nations estimates that achieving the Millennium Development Goal for sanitation could save us $66bn [£41bn] in time, productivity, averted illness and death," says Sanjay Bhatnagar, chief executive of WaterHealth International, a provider of water purification centres to developing economies.
"Every dollar spent on improving sanitation generates nine times the amount in economic benefit."
In short, an ill workforce is an unproductive workforce. Improve health, improve productivity.
Flushing loos in one form or another have actually been around since the third millennium BC, as archaeological evidence from the Indus Valley Civilisation reveals.
But modern flush toilets, which use 10 times the average daily drinking water requirement, are hopelessly unsuited to countries with poor access to water or sewerage networks.
So the world's finest scientists and inventors have been applying their technological know-how to the unglamorous but important issue, and coming up with some ingenious solutions.
In 2011, the Bill & Melinda Gates Foundation launched the Reinvent the Toilet Challenge, awarding $3.2m in grants to promising entrants.
The conditions were tough. Designs had to be hygienic, sustainable, cheap to operate, and capable of working "off-grid" - without connections to water, electricity, or sewerage networks.
Ideally, they should also be capable of reclaiming reusable materials from human waste.
In August this year, Bill Gates awarded the $100,000 first prize to Dr Michael Hoffmann, professor of environment science and engineering at the California Institute of Technology, for his team's solar-powered loo.
It uses an electrochemical reactor to break down human waste into fertiliser and hydrogen gas, which can then be stored in electric fuel cells. The treated water can be reused to flush the loo or irrigate crops.
A panel of photovoltaic cells captures light and converts it into electricity stored in rechargeable batteries. One day's light can produce enough power to run the entire electrochemical sanitation system night and day.
Human waste is channelled into a septic tank and undergoes an initial step of sedimentation and anaerobic digestion.
The "supernatant" liquid above the sediment is siphoned off into an electrochemical reactor and oxidised and the hydrogen extracted from the water.
Chloride from table salt is oxidised to form chlorine, which disinfects the water. This decontaminated water is then passed through a microfiltration system and stored.
The second prize of $60,000 went to the UK's Loughborough University for a loo that produces biological charcoal, minerals and clean water from human waste, using a process they call "continuous hydrothermal carbonisation".
This is a kind of high-pressure cooking followed by a drying and combustion process that ends up producing carbonised pellets. The dried material can be used as soil conditioner or as fuel for cooking or powering the sanitation system.
While these sustainable technological solutions are undoubtedly clever, they are relatively complex. Will they ever be affordable and simple enough for use in poor areas of developing economies?
"It's great that someone is investing in blue-sky thinking and innovation, and something good may well come out of it, but we're still left with the problem of how to provide such a service at a viable cost to poorer households," says Erik Harvey, head of programme support unit for the charity WaterAid.
But M Sohail Khan, professor of sustainable infrastructure at Loughborough University, told the BBC: "Prototypes are always expensive because they're in the experimental stages. The cost will come down in time."
He argues that moving away from centralised sewerage collection and treatment systems, with all their attendant infrastructure expenditure, to self-contained, sustainable units like his team's prototype, will also help reduce overall costs.
"Hi-tech doesn't have to mean high cost," he says.
Prof Khan also believes there will be business opportunities for firms installing and maintaining the systems, and selling on the useful minerals and by-products.
Mr Harvey agrees.
"The business opportunities are huge for entrepreneurs and communities to sell on the fertiliser and fuel by-products of these sustainable sanitation systems. This is where our focus should be, rather than on the design of the toilet itself."
Better sanitation will also confer significant commercial benefits to businesses employing healthier and more productive workforces.
Out in the open
But there is a long way to go. The UN's Millennium Development Goals (MDG) report 2012 states: "Nearly half of the population in developing regions - 2.5 billion - still lacks access to improved sanitation facilities.
"By 2015, the world will have reached only 67% coverage, well short of the 75% needed to achieve the MDG target."
Although the number of people who do not use any facility and resort to "open defecation" has decreased by 271 million since 1990, 1.1 billion people, or 15% of the global population, still have no sanitation facilities at all.
Shockingly, about 650 million people in India still practise open defecation - 60% of all who do so - despite the country's status as a rapidly growing emerging economy.
Parents are understandably reluctant to send their children - particularly girls - to schools that have no sanitation facilities.
This means young people are chronically under-educated and then join a low-skilled workforce of less commercial value to businesses, in a competitive global economy where higher skills are required.
This is why India's highest court this month ordered local authorities to build up to 100,000 "bio-degrading" toilets for pupils in all government schools within six months, using powers granted under the country's 2010 Right to Education Act.
Bill Gates writes in his blog: "In addition to building new toilets that are affordable and sustainable, we have to develop solutions to empty these new latrines and treat the human waste.
"We also have to work closely with governments, businesses, and communities to stimulate demand for better sanitation, encourage investment, and create supportive public policies that will allow these innovative solutions to succeed.
"Inventing new toilets is one of the most important things we can do to reduce child deaths and disease and improve people's lives."
Sanitation and economic development are inextricably linked. Better loos will mean big business.