The "Omniprocessor", a working prototype of which is shown in the video below, takes sewerage in one end, funnels it through a processor, boils it and then uses the dried out sewerage sludge as fuel to keep it boiling. The water vapour created from the sludge is used to power a turbine, which generates electricity, and then funneled through filters which produce clean drinking water.
The electricity can be used to power homes and entire regions surrounding the plant. The waste is collected as bacteria and pathogen free ash, which can, with proper knowledge, be used as fertilizer. It's as close to a waste free, efficient generator as you can get!
But what's truly genius about this is the way it's being sold.
Bill Gates understands that this invention can really combat the issues of sanitation, access to clean water and electrcitiy. But he understands that the impact this can have beyond just the people who use, and are supplied with energy and water from the plant, because this will, for the first time, convert sewerage and the issue of sanitation from being assocaited with a cost, to a profit.
And to get this out there, he intends to allow entrepreneurs to buy into this system and make it for profit.
This is the quickest way of getting it out there. Even if, say, the Bill and Melinda Gates were to invest $3 billion (a huge amount for the foundation - it's the total amount it gave away in grants in 2013) into this system, only 2,000 plants, or 200million people will get access to clean water. That's less than 5% of the 2.5billion urban poor who lack access to proper sewerage facilities.
Once working models get up and out there, and profit margins can be established from this (the next step after the development of the prototype in the video above), this model will take off quicker than any other! Indeed, a for-profit model has been shown to be more effective, and more likely to spread quicker than aid or government interventions, as you'll see in the video below. It also frees up more money for the Gates Foundation to spend on other projects.