In Nigeria, a country that depends heavily on revenues from its oil exports, entrepreneur Ifedolapo Runsewe has identified another type of black gold: used car tires. It has created Freetown Waste Management Factory, an industrial plant dedicated to converting old tires into paving stones, tiles and other products that are in high demand in Africa's most populous country.

The idea is to create something new from something that will remain somewhere in the form of waste was part of the motivation. Waste management in Nigeria is incomplete. In villages, towns and cities, it is common to see piles of waste, and residents often burn it at night because there is no safer way to dispose of it. Tires are routinely dumped and abandoned.