*7.4. Energy Production*

To sustain rising populations and expanding cities, the planet needs more resources. The use of waste for energy for many cities is an inexpensive, sustainable, and readily available source of energy. Because sewage treatment plants can use biogas generated from their own sludge to power their operations, they can be self-su fficient in energy. It means that the primary purpose of a sewage plant-eliminating toxins and disease-causing pathogens is not disrupted by power outages [9,15,31].
