You may be surprised to learn that the first recognition of the need for wastewater treatment occurred in 1854, with the link between improper waste treatment and a cholera epidemic was recognized. The 1972 Clean Water Act was the first official federal regulation that set specific standards for the treatment of water waste in the United States (see References 1, page 2). Wastewater facilities are under scrutiny, as governments seek to use the treated wastewater for irrigation and the treatment process to generate energy and heat.
Screen the wastewater as it enters the wastewater treatment plant to remove large items from the sewage. The goal of this step is to remove debris that could damage the treatment facility's equipment.
Remove grit from the wastewater by forcing the sewage through a grit chamber. Forcing the wastewater quickly through the chamber prevents organic waste from settling and aerates the mix. Small wastewater treatment plants may skip grit removal (see References 2).
Pump the screened wastewater into sedimentation tanks to help further separate the components of the sewage. Remove and condense the organic matter, called sludge, which settles to the bottom of the tank.
Skim the surface of the wastewater to remove oil, soap scum and grease. Rakes from the top of tanks remove these components of wastewater, known collectively as scum.
Collect the scum and sludge into a single sludge-processing unit for further treatment. Anaerobic digestion processes the solid waste, and some facilities use the resulting methane gas as a source of energy (see References 2).
Filter the wastewater through sand to remove excess iron and calcium, some bacteria and the remaining solid particles in the water. Filtering the wastewater should also reduce the color and make the water more transparent (see References 2).
Treat the wastewater with chlorine to kill remaining bacteria. Add chlorine carefully to avoid overcontamination; most of the chlorine will break down as it kills the bacteria. If necessary, treat the chlorinated wastewater with chemicals to neutralize any remaining chlorine.
Use or dispose of the cleansed wastewater, called effluent. Although treatment plants pump most effluent into rivers or oceans, some is used for irrigation purposes. As of 2008, at least 44 countries used reclaimed wastewater for agricultural irrigation (see References 3, page 29).
- National Environmental Services Center; Pipeline; "Basic Wastewater Characteristics"; National Small Flows Clearinghouse; Fall 1997
- Food and Agriculture Organization of the United Nations: Wastewater Treatment
- Food and Agriculture Organization of the United Nations; The Wealth of Waste; James Winpenny, et al.; 2010
Amy A. Whittle is a freelance writer who specializes in home improvement, green living and pet care issues. Her work has been published by Woman's Day.com, the Huffington Post and other online and print publications.