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Sewage and Sewer Systems

Sewage (also called wastewater) refers to the liquid and solid waste, usually containing human excrement, that is refused from a home, business or industry. Sewer systems are designed to dispose of human, household, and industrial waste in a manner that reduces human contact with harmful pathogens and toxins, decreases exposure to unpleasant sights and odors, and reduces the environmental impacts of dumping sewage directly into the physical environment. Modern sewer systems consist of various sizes of underground pipes that lead to a sewage treatment plant so treated sewage effluent can be safely returned to rivers and other waterways. Sewer systems may also require the use of lift or pump stations to move sewage from lower to higher elevations, while manholes provide access to sewer systems for maintenance and construction purposes.

Sewage contains a variety of dissolved and suspended materials, including organic compounds and nutrients, viruses, bacteria, other pathogens, paper, feminine hygiene products, food, and grease. The term sanitary sewage is used to refer to wastewater leaving a home or business that contains human waste and general refuse water from toilets, sinks, and drains. Sanitary sewage may be combined with wastewater from storm sewers, which may contain other components such as leaves, cigarettes, small animals, and toxins from streets and parking lots.

Residences or businesses that are not located near a sewer system or sewage treatment plant may use septic systems that store and treat sewage (usually through biological processes) or alternative sewage treatment methods (such as the application of sewage that has received primary or secondary treatment on agricultural fields or golf courses). Most urbanized areas and industrialized countries have specific regulations and policies regarding the disposal and treatment of sewage and other wastewaters, though proper disposal of sewage and wastewater remains one of the most costly and challenging environmental and health concerns worldwide. Water previously containing sewage is often discharged back into surface waters after sewage treatment, making sewage treatment particularly important for general water quality and drinking water supplies as well.

Early and Modern Sewer Systems

Early forms of sewer systems date as far back as 4000 to 3000 b.c.e. in the Indus Valley, Mesopotamia, Scotland, and Crete. The earliest sewer systems usually consisted of holes or latrines that held human waste, which were sometimes connected to a system of sewer lines to remove the waste from homes and other buildings. Rome developed an extensive sewage system of latrines and sewer lines from approximately 800 b.c.e. to 300 c.e. Despite some of these extensive developments in sewer systems in early civilizations, discharging untreated sewage directly into surface waters was the primary method of wastewater disposal for many communities through the 19th century, where the contaminants and odors present in sewage could be diluted in large waterways. Other cities allowed sewage to be discharged in or near public spaces and streets through the 17th century.

Sewage sanitation and treatment methods were not widely employed until after the Middle Ages, when diseases and epidemics were traced to poor hygiene and exposure to human wastes. During the 16th and 17th centuries, cities such as Paris, London, and Hamburg began to develop sewage disposal systems to reduce public contact with human waste. In the United States, sewer systems began to be built by private individuals and public services in the mid 1700s in cities such as Boston.

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