Urban household sewer water, processed to remove solid waste and some of the organic matter, is being used in Brazil as a fertilizer that boost sugarcane yields 50 percent. The technique, under development since 2005 by agronomist Rafael Leal at the University of São Paulo, has also proved effective for maize, coffee and sunflower crops.

The wastewater is rich in nitrogen and phosphorous, which is why it triggers algae blooms and fish die-offs in rivers. But, “when used in agriculture, this risk is avoided and we make the most of the nutrients,” Leal explained to Tierramérica. However, this type of irrigation cannot be used for products that are consumed raw, he warned.

This approach merits public subsidies, he said, because it benefits human health and the environment, as well as reducing the need for chemical fertilizers.