ABSTRACT
Energy consumption is constantly increasing all over the world. According to International Energy Agency (IEA), from 1990 to 2008 the average energy use per person increased 10% while world population increased 27%. It is expected that by the year 2035, energy consumption will be doubled [18]. On the other hand, potable water and wastewater treatment plants are also the largest energy consumers. According to the US Environmental Protection Agency (EPA), wastewater and drinking water treatment account for 4% of the energy use and emit over 45 million tons of greenhouse gases annually in the United States alone. Aerobic wastewater treatment is an energy-intensive process and emits nitrogen into the atmosphere. Nitrogen is generally used in the production of fertilizer and it takes enormous amounts of energy to recapture the nitrogen from the atmosphere [18]. Moreover, considering the increased fuel cost, global warming issues, and environmental pollutions, biosolids and biogas are great energy sources that can be derived from wastewater resources. Innovative technology is progressing in the direction of energy recovery, bio-solid management, odor reduction, and pathogen reduction in bio-solids. Anaerobic digestion for biogas generation is already used for industrial or domestic purposes such as producing fuel and waste management. Biogas produced from animal and human waste is a reliable source of energy and its use is growing in China, India, Nepal, and some western countries [2,19]. Similarly, bio-solids are rich in organic matter and nutrients, which are predominantly used as fertilizer. Dried sludge also can be used as a direct source of fuel in the industries. Furthermore, one of the important properties of the water is that it retains the temperature; water can transfer hot or cold temperature eciently when it is in contact with other objects. By taking advantage of this characteristic of water, Japan
is saving 20%–30% of energy in the municipal government of Osaka. e temperature of the sewage treatment facility is relatively warmer in the winter and colder in the summer than the ambient temperature. Japan has developed a heating and cooling system with wastewater as an alternative source of energy [19].
