(By Erika Herz, Associate Director of Sustainability Programs at the University of Virginia Darden School of Business, and Andrea Larson, a professor of entrepreneurship at Darden; adapted from an original Darden case by Larson and Mark Meier) The big idea: Entrepreneur Brent Constantz, a coral reef scientist, was well aware of the destructive effects of carbon dioxide (CO2). In 2007, he founded Calera Corp. to make cement, the main binder for concrete, by mimicking nature’s low-energy process. The company soon discovered a host of other waste reuse, waste reduction and revenue-generatin...