| Summary: | An underappreciated source of renewable energy is wastewater, both municipal and industrial, with global production exceeding 900 km<sup>3</sup> a year. Wastewater is currently perceived as a waste that needs to be treated via energy-consuming processes. However, in the current environmental nexus, traditional wastewater treatment uses 1700–5100 TWh of energy on a global scale. The application of modern and innovative treatment techniques, such as microbial fuel cells (MFC), would allow the conversion of wastewater’s chemical energy into electricity without external energy input. It has been demonstrated that the chemically bound energy in globally produced wastewater exceeds 2.5 × 10<sup>4</sup> TWh, which is sufficient to meet Europe’s annual energy demand. The aim of this paper is to answer the following questions. How much energy is bound in municipal and industrial wastewaters? How much of that energy can be extracted? What benefits will result from alternative techniques of waste treatment? The main finding of this report is that currently achieved energy recovery efficiencies with the use of microbial fuel cells technology can save about 20% of the chemical energy bound in wastewater, which is 5000 TWh on a global scale. The recovery of energy from wastewater via MFC technology can reach as much as 15% of global energy demands.
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