"Why is it waste?" asked Zhen (Jason) He, a professor at Washington University in St. Louis. "It's organic materials," he said, and those can provide energy in a number of ways.

Then there's the other valuable resource in wastewater.

Water.

His lab has developed one system that recovers both, filtering wastewater while creating electricity. Results from bench-scale trials were published in May and featured as a front cover article in the journal Environmental Science: Water Research & Technology.

The waste materials in wastewater are full of organic materials which, to bacteria, are food.

"Bacteria love them and can convert them into things we can use," He said. "Biogas is the primary source of energy we can recover from wastewater; the other is bioelectricity."