Sustainable Wastewater Treatment

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Hydrology, the science of water systems, has always been a central part of environmental engineering. Ancient societies used flowing water as a means of travel, a conveyance for moving timber and other goods downstream, and a waste disposal system. During the growth of civilization, people learned that bodies of water held a significant amount of force. Villages constructed mills next to fast flowing rivers to let the force of the water supply power for the milling operations. The next generation built enormous dams to control the force of water that powered turbines and produced electricity. Water systems will become part of new energy-generating systems in sustainable communities in the near future, mainly because water avoids the use of nonrenewable and pollution-causing fossil fuels.

Wastewater treatment follows a standard process that turns raw sewage into disinfected water safe for return to the environment. Almost all modern wastewater treatment plants conduct the following steps to treat wastewater: (1) wastewater passes through screens that remove large solids; (2) wastewater enters a grit chamber where heavy wastes settle out of the water by gravity; (3) water enters a larger settling tank where light, small particles slowly settle out of the water; (4) the water enters an aeration tank containing aerobic (oxygen-requiring) bacteria that digest organic substances, aided by a constant bubbling of air through the contents; (5) the water enters another settling step and then passes through a filtration tank, which removes very fine particles; (6) disinfectant kills the bacteria in the water; and (7) the treated water discharges into the environment.


Pipes carry much of the heavy organic sludge that collects in the settling tanks to another tank called an anaerobic digester. This digester contains anaerobic (requiring the absence of oxygen) bacteria that slowly degrade the heavy sludge and produce methane and small amounts of other gases. The wastewater treatment industry calls the methane biogas, and both biogas and solid biomass serve as energy sources produced by wastewater treatment.