Toronto Star: A mixture of hot gas rises out of a flue stack at the St. Marys Cement plant about 50 kilometres west of Waterloo. But not all the CO2-rich exhaust is vented to the open air. Some is redirected through a 15-centimetre thick pipe connected to the side of the stack. The pipe carries the gas into a high-tech facility where a species of algae from the neighbouring Thames River uses photosynthesis to absorb the carbon dioxide and release oxygen in return. "It’s a small model of what …