According to this article in the Guardian, scientists are looking at extracting valuable metals from human waste.

Sewage sludge contains traces of gold, silver and platinum at levels that would be seen as commercially viable by traditional prospectors. “The gold we found was at the level of a minimal mineral deposit,” said Kathleen Smith, of the US Geological Survey.
Smith and her colleagues argue that extracting metals from waste could also help limit the release of harmful metals, such as lead, into the environment in fertilisers and reduce the amount of toxic sewage that has to be buried or burnt.

Bad jokes aside, this is actually an interesting concept. It also reinforces the concept that as the price for a commodity rises, human ingenuity will come up with new ways to access those commodities. 

In this case, the commode. (Sorry, couldn’t help myself).