Pond scum – algae – gained prominence a few years ago, emerging from research obscurity to hog the green limelight. With questions over growing food crops for biodiesel and concerns over fuel security and global warming, algae seemed to offer a renewable, carbon-neutral source of fuel. Algal cultivation could use a large amount of non-arable land without harming food production, said the sales pitch, and its demand for water could be met with non-potable supplies, even saline or wastewater. As algal biochemist Alison Smith of the University of Cambridge, UK, explains, ‘I was being phoned up every five minutes by...