Star Tribune: There were chuckles a few years ago when University of Minnesota researcher Roger Ruan set up a tiny still in his biofuels lab to experiment with oily strains of algae. This week, ExxonMobil and a partner, Synthetic Genomics, announced they would invest $600 million to develop bio-based diesel fuel from algae, which can be fertilized with carbon dioxide from power plants. Ruan has a similar experiment going at a pilot plant next to a Metropolitan Council sewage treatment plant …