With growing populations and ever-increasing global water consumption, the challenges of treating wastewater are also growing. Many environmental problems are associated with the disposal of sewerage. According to the United Nations World Water Development Report 2017, the vast majority of global effluents is released directly into rivers and oceans without adequate treatment. Pollution, the disruption of aquatic ecosystems through eutrophication, and the contamination of freshwater supplies are just a few of the numerous negative consequences. However, wastewater has a high content of energy, as well as nutrients that can be extracted; the sludge from treatment units can be subjected to anaerobic digestion, together with other organic wastes, and wastewater can also be treated with organisms like bacteria and algae in order to enhance carbon utilization, the production of biomass and removal of nutrients. Secondary effluents from treatment plants can even be used for biofuel production through algae. The amount of energy that can be recovered this way can exceed the required treatment energy by up to tenfold. Therefore, wastewater can also be viewed as a resource rather than a problem
Sources: United Nations Environment Programme: The United Nations World Water Development Report 2017. Wastewater: The Untapped Resource, 2017.
Gude, Veera Gnanenswar: Energy positive wastewater treatment and sludge management, in: Edorium Journal of Waste Management, vol. 1, (2015).