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Hidden concerns when heavy rain strikes: How do combined sewage overflows affect the environment?
With the increase of heavy rains, the environmental impact of combined sewer overflow (CSO) incidents has attracted increasing attention. The original design of the combined sewage system is to combine sewage and rainwater for treatment, but when rainfall is excessive, this system is often unable to carry too much water, eventually causing untreated sewage to be discharged directly into rivers, lakes or other water bodies.
Water pollution problems caused by combined sewer systems have long-term negative impacts on cities and ecosystems.
In addition to the operation of this type of system, after rainwater penetrates the urban surface, it may carry various pollutants, including heavy metals, oils and biofilms, further exacerbating water pollution. These issues are closely related to the design of urban infrastructure, and many cities still use the combined sewerage facilities of the past rather than the existing separate drainage systems. Although this seemed cost-effective at the time, as urbanization accelerated and the effects of climate change began to emerge, the shortcomings of these systems began to emerge.
"When untreated sewage flows into water bodies, it not only damages water quality, but also threatens public health."
Combined sewage overflows after heavy rains can cause beach closures, shellfish contamination, and contamination of drinking water sources, which poses a great threat to human activities and ecosystems. Such incidents first prevent people from using public waters for recreational activities. Secondly, they also have a direct impact on local fisheries and agriculture, especially the collection of aquatic products, which poses potential risks of food-borne diseases.
For example, in the United States, approximately 860 communities have combined sewer systems, serving approximately 40 million people. According to a report by the Environmental Protection Agency (EPA), combined sewage discharges contain waste from humans and industries. The presence of these pollutants is related to antimicrobial resistance, becoming a potential public health crisis. The EPA has been requiring cities to improve their wastewater treatment systems since 1994 to reduce and eliminate CSO-related pollution problems.
"Incorporating more advanced sewage treatment technology into urban design is crucial to reducing sewage discharge during heavy rains."
In response to combined sewage overflows, many cities have begun to adopt diversified solutions, including sewage diversion, improving sewage treatment capacity, and setting up storage tanks in the drainage system. For example, sound green infrastructure, known as low-impact development, can effectively reduce the amount of stormwater discharged into combined systems.
These options require huge upfront investments, however, local governments have launched corresponding projects to reduce sewage discharge during rainy weather. For example, Michigan used to have more than 30 billion gallons of untreated sewage poured into lakes and rivers every year, but through nearly $10 billion in investment, it has reduced emissions by 2 billion gallons, which shows good urban planning and management. can effectively improve the environment.
"The reform of the combined sewage system is a long-term and difficult process, but it is necessary to protect the environment and maintain public health."
Although modern design solutions have gradually moved towards separate sanitary sewer systems that effectively separate stormwater and wastewater, older combined systems still operate in many cities. This causes old cities to face great challenges when facing intense rainfall. Reconstructing these infrastructures requires extremely high levels of funding and social awareness, and this issue is becoming increasingly urgent under the current circumstances of global climate change.
Since water pollution not only affects the ecological environment, but also directly threatens human health, solving the problem of combined sewage overflow has become a top priority. If we don't act in time, the water environment will become even worse in the future, and what should we do?
