Read this: Since the launch of the "Reinvent the Toilet Challenge", more than a dozen research teams, mainly at universities in the U.S., Europe, India, China and South Africa, have received grants to develop innovative on-site and off-site waste treatment solutions for the urban poor. The grants were in the order of 400,000 USD for their first phase, followed by typically 1-3 million USD for their second phase; many of them investigated resource recovery or processing technologies for excreta or fecal sludge.

What did the Reinvent the Toilet Challenge investigate?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable