Even in urban areas, where household and communal toilets are more prevalent, 2.1 billion people use toilets connected to septic tanks that are not safely emptied or use other systems that discharge raw sewage into open drains or surface waters.

Thus, the foundation extended its global "toilet revolution" campaign to China, kicking off a competition with grants of $5 million to encourage Chinese talent to reinvent the toilet.

"Imagine each person discharges 1.5L urine and 300g of feces per day, and if you multiply the number of people of Beijing, how much stuff has to be processed on a daily basis," Hoffmann said.

The processing is a huge project and demands large scale applications, instead, small facilities like his invention could do the job in each home, he said.

Hoffmann said he visited Houhai, a bar area in Beijing's hutongs, and saw how people use public toilets. "They can have one unit of their own outside their doors and it does not need water or electricity. People will be shitting in their house instead of going out. And one can even charge others for using it."

Hoffmann has been dealing with human waste for about 20 years. "If you want to study something, you have to invite it to your lab. Yes, all my students and even my brave wife have contributed to my research," he said.

Sometimes, the experiments went wrong.

"Yeah, people make mistakes and they forgot to do something. And it just ran out on the floor. They had to clean up the human waste with their hands," the professor said pulling a face.

Hoffmann said his invention is expensive as research has cost a lot. He has been seeking partners in China to manufacture the product in large numbers, which would reduce costs.

He introduced his invention to industry companies and toilet designers in Beijing, and named his presentation slides "shit show." He asked the audience to "put our shits together" for the new "p-power."

The Caltech team have been trying to work with an electric car company on battery applications.

"In future maybe you can power your car with your own poop. If you feel your production is not enough, you can invite some of your friends to watch television at your home," he suggested.