Erillisviemärijärjestelmiä

Erillisviemärijärjestelmiä, known in English as separate sewer systems, are a type of municipal wastewater management infrastructure. Unlike combined sewer systems, which carry both sanitary sewage and stormwater runoff in a single pipe, separate sewer systems utilize distinct networks for each type of wastewater. One system, typically called the sanitary sewer, collects wastewater from households, businesses, and industries. This collected wastewater is then transported to a wastewater treatment plant for purification before being discharged. The second system, known as the storm sewer or drainage system, collects rainwater and surface runoff from streets, roofs, and other impervious surfaces. This stormwater is generally discharged directly into local waterways, such as rivers, lakes, or oceans, without undergoing treatment, as it is considered less contaminated than sanitary sewage.

The primary advantage of separate sewer systems is the prevention of combined sewer overflows (CSOs). In older combined systems, heavy rainfall can overwhelm the capacity of the pipes and treatment plant, leading to untreated sewage and stormwater being discharged directly into the environment. Separate systems mitigate this problem because the sanitary sewer is not burdened by stormwater, ensuring that sanitary sewage can be treated even during storms. This leads to improved water quality and reduced pollution of receiving waters. However, building and maintaining two separate systems can be more complex and costly than a single combined system. Furthermore, leaks in either system can still pose environmental risks; leaks in the storm sewer can carry pollutants into waterways, while leaks in the sanitary sewer can contaminate groundwater.