Flushing Energy?

In the United States water and wastewater treatment plants are net users of energy. According to the Environmental Protection Agency, in 2008 water and wastewater utilities consumed about 75 billion kWh of electricity (2 percent of the total electricity generated that year), costing over $4 billion to pump, treat, deliver, collect, and clean water.  However, some studies indicate that wastewater contains about 10 times the energy needed to treat it.  Indeed, elsewhere in the world raw sewage is used to produce electricity (Figure 2), using as a resource something we are currently treating as waste. Most treatment plants in the United States are currently using 1970s technologies, and are in need of repair.   According to Bruce Logan, a Penn State University environmental engineer, “If animal, food industry and domestic wastewaters were combined together, they could provide roughly 500 trillion British Thermal Units (BTUs) of energy,” which is about one half of one percent of our current annual energy use.  Thus, not only can water waste treatment plants in the United States become energy self-sufficient if the proper technology is employed, but they can also generate excess power that can be sent back into the grid. Today, the two most widespread technologies for exploiting sewage as an energy resource are:  (a) Sludge Incineration, which often finds strong opposition due to fears about impacts on human health; and (b) Anaerobic Digestion, were bacteria degrade sludge in the absence of oxygen to produce biogas, a mixture of methane (65 percent), carbon dioxide (about 30 perfect), and other gases like hydrogen sulfide and water. Among other applications, biogas can be employed for heating, to generate electricity, or as a vehicle fuel. Also, the capture of these gases also prevents potent greenhouse gases from being released into the atmosphere larger proportion of sewage as an energy generation source. According to The Economist, Germans already process about 60 percent of their sewage for such purposes, with the Czechs, Britons and Dutch close behind.  By the end of 2010, Britain expects to process about 75 percent of their wastewaters (enough to power 350,000 homes),  and in Spain, waste could soon supply about 7 percent of electricity demand. Even in the developing world (especially in India, Mexico and South America) villagers and farmers increased their use of simple technologies to convert animal and human wastes to biogas for cooking, heating and farming. Several groups are testing ways of making the process of biogas generation much more efficient, many motivated by a desire to find renewable energy alternatives. In Europe, Germany and Great Britain are far ahead in the development of new technologies.  GENeco, a subsidiary of a British utility company, uses a two-tank system were different strains of bacteria decompose the wastes, producing about 30 percent more methane than conventional methods. The Fraunhofer Institute in Stuttgart employs a pumped system which mixes the sludge, reducing the amount of time it takes to digest sewage from two weeks to one.  This system, already deployed in 20 water treatment plants in Brazil, Germany and Portugal, operates for few hours a day, thus not requiring for its use a large amount of energy. In the United States, two Stanford University scientists are working on an energy-neutral/emissions-free sewage treatment process, bridging two very different fields — space propulsion and environmental biotechnology. The process consists of creating a low-oxygen environment in the treatment plant, and favoring the growth of nitrous oxide-producing bacteria while aerobic species die off.  This will increase the production of methane and nitrous oxide to power the sewage treatment plant and small rocket thrusters, respectively. Also, Oregon State University engineers are using nanotechnology to develop electrochemical cells for sewage treatment.  By coating graphite anodes with gold nanoparticles, they have been able to extract 20 times more electricity than in previous similar laboratory experiments. Furthermore, according to the researchers the technology could also generate hydrogen gas. A recent joint publication by Duke University and the University of Texas at Austin estimates that exposing wastewater to anaerobic digestion could save 628 to 4,940 million kWh annually in the United States.  And the potential gains seem even larger for the developing countries, where sewage often goes untreated and electricity generation capacities are frequently limited. http://energypolicyinfo.com/2010/08/flushing-energy/