At a sprawling sewage treatment plant in north San Jose, engineers are slowly perfecting the ideal temperature for a smelly mixture of bacteria and human waste as the stew churns inside four massive air-tight cauldrons. The plant, the largest wastewater treatment facility west of the Mississippi to produce water clean enough to be discharged into a sensitive ecosystem like San Francisco Bay, is experimenting with new heat-loving bacteria that excel at turning poop into compost and energy — harnessing the power of dangerous greenhouse gases