By: Sophia S.
Combined sewer overflow Photo from: Clean Water Action
Roadside sewer trenches, cesspools near markets, and human excrement being chucked out of windows: sewage used to be a prominent fixture in many urban settings. Introduced in the mid 1850s, though, the combined sewer system was hailed as an amazing improvement for moving waste underground.
Combined sewer systems have one pipe where domestic sewage, industrial wastewater, and stormwater runoff combine and are sent to a wastewater treatment facility before being discharged into local bodies of water. While the combined sewer is an incredible advancement, increasing populations have outgrown the original sewage infrastructure and rain can easily overflow pipes. In some cities, this only takes a quarter-inch of rain. To avoid flooding streets and homes, combined sewers dump excess raw sewage directly into local waters in events called combined sewer overflows (CSOs). According to the EPA, CSOs result in an estimated 850 billion gallons of untreated wastewater being dumped into US waterways each year.
Diagram of combined sewer system showing CSO Photo from: WGI
The most well-known component of wastewater is our excrement, which can be extremely harmful. With feces comes fecal coliform, bacteria like E. coli and V. cholerae. When people swim in or ingest wastewater, these bacteria can cause diseases including Cholera and Salmonella. While most animals aren’t affected by these diseases, humans will experience intense diarrhea and vomiting, and possibly death. The gut flora (intestinal bacteria) that feces contains can also cause coral bleaching disease. With so many marine organisms relying on corals for food and shelter, the destruction of corals can unfortunately lead to the destruction of a whole ecosystem. Drugs that pass through the body and into waste (or drugs that are directly flushed) can have many effects on fish, from hurting their development and reproduction to inducing hyperactivity and overeating. These drugs can also shift microbial diversity.
Along with feces, untreated wastewater also contains chemicals and litter that cause biomagnification. Heavy metals, chemicals, and toxin-leaching litter that are dumped can enter the food chain and poison aquatic life. Through biomagnification, these toxins move up the food chain, occur in higher and higher concentrations at each level, and eventually cause serious damage and death.
Raw sewage dumping can also contribute to creation of dead zones, areas with extremely low oxygen concentrations. When sewage is dumped, natural bacteria in the water break it down, using oxygen in the process. The more sewage there is, the more oxygen is sucked up. Nitrogen and phosphorus rich products like fertilizers can combine with wastewater in runoff and when dumped, have the potential to create dead zones by attracting algae that lead to the leaching of oxygen.
In an effort to eliminate CSOs, the separate sewer system was introduced. In this system, one pipe carries stormwater directly to local bodies while another carries sanitary sewage and industrial wastewater to a wastewater treatment facility. Though sewer separation stops raw sewage from being discharged into waterways, pollution from stormwater runoff increases because the water is never treated. However, though runoff discharge increases, there have still been visible pollution decreases in cities switched to separate sewer systems. In Massachusetts, for example, there was a 45% reduction in fecal coliform. Even more drastically, Minnesota had a 70% reduction in fecal coliform and fish diversity recovered from 3 species to over 25.
Diagram of a separate sewer system. Photo from: City of Alexandria
While the benefits of a separate sewer system are clear, updating infrastructure from a combined sewer system proves difficult. In 2004, the EPA estimated that it would take $88.8 billion to eliminate CSOs, meaning that high budgets are needed to make the switch. Government programs such as the Clean Water State Revolving Fund, which lets states get low interest loans for water infrastructure updates, are allowing the US to start improvements. Unfortunately, funding still remains lower than needed and combined with the inconvenience of mass construction, progress has been limited.
Many cities that haven’t been able to make the switch are still taking strides towards reducing sewer overflow. Cities like Chicago and Atlanta have built large storage tunnels to increase sewer capacity and limit overflow. Other cities, like Phillidelphia, are turning to green infrastructure. Installing rain gardens, green roofs, permeable pavements, and increasing overall vegetation helps mimic the natural water cycle. This limits the amount of rain flooding sewers by absorbing and filtering water that otherwise would have slid off concrete.
On the individual level, if you live in an area with a combined sewer system, you can help reduce sewage overflow by decreasing your water usage. This can be done by taking shorter showers, flushing less, turning off and fixing facets, or delaying laundry and dishwashing on days of heavy rainfall. If possible, you can also install rain barrels to downspouts and collect rain to prevent it from reaching sewers.
While progress may be slow, each day we get closer to eliminating combined sewer overflow and keeping our aquatic ecosystems clean and healthy.
Discussion Questions:
Do you live in an area with a combined or separate sewer system?
Is the government doing enough to fund water infrastructure projects?