Toilet that uses little or no water is expected to improve sanitation in the developing world.
US billionaire and philanthropist Bill Gates is investing in a solar-powered toilet for the developing world that will use little or no water.
The need for a new type of toilet is an important part of the Bill & Melinda Gates Foundation's push to improve health in the developing world, officials familiar with the project said.
Last year the foundation, named after the Microsoft co-founder and his wife, gave grants to eight universities around the world to help create a hygienic toilet that is safe and affordable and can transform waste into energy.
The project challenged inventors to come up with a toilet that operated without running water, electricity or a septic system.
It needed to operate at a cost of no more than five cents a day and would ideally capture energy or other resources.
Open defecation leads to sanitation problems that cause 1.5 million children under five to die each year.
The eight universities, led by Professor Michael Hoffman, designed a toilet that generated hydrogen gas and electricity. They won a $100,000 prize.
Waste to electricity
At the Reinvent the Toilet fair, hosted in Seattle this week, designs included a lavatory that used microwave energy to turn human waste into electricity.
Another turned excrement into charcoal, while a third used urine for flushing.
In total 28 designs were shown off at the fair and the winner was a team from the California Institute of Technology.
Gates said toilet technology had not fundamentally changed since the invention of the flush toilet in 1775.
"Imagine what's possible if we continue to collaborate, stimulate new investment in this sector, and apply our ingenuity in the years ahead," Gates said at his foundation's Seattle headquarters.
"Many of these innovations will not only revolutionise sanitation in the developing world, but also help transform our dependence on traditional flush toilets in wealthy nations."
Gates' foundation announced $3.4m in new funding on for toilet projects being worked on by various organisations, bringing total investment in its "Reinvent the Toilet Challenge" to about $6.5m.
About 2.6 billion people - or 40 per cent of world's population mostly in sub-Saharan Africa and south Asia - lack access to safe sanitation and are forced to defecate in the open, according to Gates.