Never heard of this before. Sounds like electrons from microorganism poop?
Project called the MudWatt.
https://www.kickstarter.com/projects/1073149387/mudwatt-build-your-own-battery-that-runs-on-mud?ref=nav_search (https://www.kickstarter.com/projects/1073149387/mudwatt-build-your-own-battery-that-runs-on-mud?ref=nav_search)