Who says pollution clean-up has to pay for itself?

In a world searching for more sustainable ways to manage waste, the promise of turning "trash into treasure" is hard to ignore. Take nitrate pollution, for example. Every year, nitrogen fertilizers help feed billions of people. But not all of that nitrogen stays where it is needed. Some is washed from farms into rivers, streams and groundwater, where it can contribute to environmental problems, including harmful algal blooms.