Seite - 88 - in Clean Water Using Solar and Wind - Outside the Power Grid

88 Clean Water Using Solar and Wind: Outside the Power Grid suffocate and the process rate will be significantly reduced. In extreme cases the organisms will die. The opposite applies to denitrification: the higher the level of dissolved oxygen, the lower the rate. Aeration typically represents 50% to 60% of a sewage treatment works’ energy demand but energy consumption as high as 75% has been reported. This fact explains why aeration control is key to saving energy (Olsson, 2015). Since urine accounts for most of the nitrogen in used water, urine separation eliminates the need for nitrification and denitrification, as noted in the previous section. It also lowers the energy demand for the organic matter. Obviously, there are more energy-efficient methods to use in remote areas than the activated sludge process. Electric energy should be used for purposes other than oxidising organic matter. Instead, the inherent energy in organic carbon should be converted to useful energy via anaerobic digestion to produce biogas. 7.2.3 Anaerobic digestion Simple home- and farm-based anaerobic digestion systems offer the potential for cheap, low-cost energy for cooking and lighting by producing biogas. The organic material that provides the feedstock for the anaerobic digestion may consist of faeces and blackwater, manure from pigs and cows, food residues and agricultural residues. The production of biogas from anaerobic treatment is a key component in resource recovery. The biogas can be converted into energy, for example to provide heat for cooking. Anaerobic bacteria are some of the oldest forms of life on earth. The same types of anaerobic bacteria that produce natural gas in nature also produce methane in the technical processes. Anaerobic bacteria evolved before the photosynthesis of green plants released large quantities of oxygen into the atmosphere. Anaerobic bacteria break down or “digest” organic material in the absence of oxygen and produce biogas as a waste product. Anaerobic decomposition occurs naturally in swamps, waterlogged soils and rice fields, deep bodies of water and in the digestive systems of termites and large animals. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user