Sewage and Sewer Systems Essay

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Se wage (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.

Today, three primary types of municipal sewer systems are used in the United States, including combined sewers, separate sanitary sewers, and separate storm sewers. Combined sewer systems (CSS) are designed to carry sanitary sewage (domestic, industrial, and commercial wastewater) and storm water runoff through a single sewer pipe to a wastewater treatment plant. Municipal separate sanitary sewer systems (SSS) convey only domestic, industrial, and commercial wastewater (sanitary sewage) to a wastewater treatment plant, and are not designed to carry large amounts of storm water runoff. Instead, separate storm sewer systems are used to carry storm water runoff directly into nearby waterways.

Cities in the United States may have both combined sewer systems and separate sewer systems, or they may have only separate sanitary and storm water sewer systems. Cities with separate storm and sanitary sewers may offer little or no treatment of storm water before discharging it into local waterways, meaning that high levels of toxic pollutants from streets and parking lots can be released into surface waters. Separate sanitary sewer systems are the most predominant type of wastewater collection system in the United States today, although combined sewer systems are often found in older communities in the United States. Estimates from the U.S. Environmental Protection Agency (EPA) value all of the county’s sewer systems at more than $1 trillion.

Sewers and Sewage Treatment

Sewage treatment may contain several steps, ranging from preliminary treatment to remove large objects such as sticks, rocks, food, and paper debris, to tertiary treatment involving the use of chemical processes. Primary sewage treatment refers to the removal of suspended solids through the use of screens and settling tanks. The solid materials that settle out of raw wastewater are referred to as sludge (or biosolids), which can be treated using biological processes and disposed of in landfills, incinerated, or in some cases applied to land as fertilizer. Once thought of as an acceptable disposal method, the application of treated biosolids containing human waste has fallen out of favor in the United States during the past decade amid concerns about pathogens and other toxins.

After wastewater has received treatment through screening and settling, it may also receive secondary sewage treatment where microorganisms are added to the wastewater to consume dissolved organic compounds. Pathogens and other harmful materials can be removed through tertiary treatment and disinfection methods, such as the addition of chlorine to wastewater or exposing the effluent to ultraviolet light. Wastewater containing high nutrient loads may require the removal of nitrogen and phosphorus to avoid excessive biological growth in receiving waters.

Sewer Overflows

One of the biggest environmental concerns regarding sewer systems in the United States is the occurrence of sewer overflows, which can pollute local waterways and expose communities to potentially harmful viruses, bacteria, and other pollutants. The EPA recognizes two main types of sewer overflows: Combined sewer overflows (CSOs) and separate sanitary overflows (SSOs). A combined sewer overflow is the release of sanitary sewage and storm water from a combined sewer system prior to treatment at a wastewater treatment facility. Generally, a combined sewer system functions properly by transporting all sanitary wastewater and storm water through a single pipe to a treatment facility, where it is cleaned and released into nearby waterways. However, during episodes of heavy rainfall or snow melt, a combined sewer system may exceed its designed capacity, requiring the discharge of excess untreated sewage, wastewater, and storm water directly into local streams and rivers through designated release points. Combined sewer systems and CSOs are typically associated with older communities and wastewater infrastructure that was built prior to major federal water quality regulation, which did not appear in the United States until the late 1950s. Because CSOs are a point source of water pollution, they are legal discharges regulated by the Clean Water Act through National Pollution Discharge Elimination System (NPDES) permits. It has been estimated that individual CSOs release approximately 1.2 trillion gallons of raw sewage and wastewater in the United States every year.

A sanitary sewer overflow (SSO) is the unintentional and unauthorized discharge of untreated raw sewage from a separate sanitary sewage system due to sewer system malfunctions. SSOs generally occur at manholes, releasing untreated wastewater into roadways, waterways, and onto public and private property, but SSOs can also occur at sewer hookups located in the basements of private homes, directly exposing residents to untreated raw sewage. The EPA estimates that at least 40,000 SSOs and 400,000 basement SSOs occur in the United States every year, which can contaminate surface waters, cause private property damage, and pose significant public health risks. Importantly, sanitary sewer overflows are illegal under Section 301 of the Clean Water Act, which prohibits the discharge of pollutants into U.S. waterways without a permit. As such, the true number and volume of SSOs may not be the EPA.

Human health risks of CSOs and SSOs result primarily from exposure to overflow discharges, including contact with untreated sewage in streets, lawns, and parks, or through recreational activities such as swimming in water bodies that receive SSO discharges. Human exposure can also occur from contaminated drinking water sources or the consumption of shellfish that have been harvested from contaminated waters. Diseases that have been identified in SSOs include the stomach flu, cholera, dysentery, and hepatitis B. Water quality and ecosystem health are also affected by sanitary sewer overflows, including habitat degradation, harmful algae blooms, lowered dissolved oxygen levels, and fish kills. Sewer overflows have also been identified as one of the primary cause of swimming advisories and beach closures in the United States. Addressing sewer overflows through the replacement and upgrading of increasingly antiquated sewer systems remains one of the most persistent and challenging environmental and social problems in the United States.

Political Economy of Sewer Systems

Sewage treatment is primarily the responsibility of local and regional governments in the United States. The expenses associate with constructing and maintaining sewer systems require public consensus regarding the level and quality of sewage treatment a community wishes to provide for its wastewater. At the same time, sewage has become a significant economic activity with various companies and manufactures offering numerous treatment and management options. Sewage, despite its unpleasant nature, is both big business and major public policy.

In many ways, sewage and sewer systems sit at the very intersection of the physical environment and human society. For centuries, communities have had to negotiate the processes of urbanization and development-which concentrate and increase the amount of sewage in an area-with the impact of sewage on natural processes and living organisms, economic requirements for the construction and maintenance of sewer systems, policies to protect human health and ecosystem viability, as well as public perceptions regarding sewage. For something that rarely comes up in the conversations of everyday residents, sewage and sewer systems are particularly important and ubiquitous aspects of both the environment and society.


  1. Field, D. Sullivan, and A. Tafuri, Management of Combined Sewer Overflows (Lewis Publishers, 2004);
  2. Jon C. Schladwelder, “Tracking Down the Roots of Our Sanitary Sewers,”;
  3. Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations (CRC Press, 2003);
  4. S. Environmental Protection Agency (EPA), Sanitary Sewer Overflows: What are They and How Can We Reduce Them? (Office of Wastewater Management, 1996);
  5. S. EPA, Report to Congress: Implementation and Enforcement of the Combined Sewer Overflow Control Policy (Office of Water, 2001);
  6. S. EPA, Wastewater Management: Controlling and Abating Combined Sewer Overflows (Office of Inspector General, 2002).

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