Sekaviemäriä

Sekaviemäriä, also known as a combined sewer, is a type of sewage system that carries both sanitary sewage and stormwater runoff in a single pipe. This design was common in many older urban areas, where separate systems for wastewater and rainwater were not initially implemented. The purpose of a combined sewer is to transport all water from a given area to a wastewater treatment plant.

During dry weather, the combined sewer primarily carries sanitary sewage from homes and businesses, along with some infiltration from groundwater. However, during rainfall events, the volume of water in the system increases dramatically as it collects stormwater from streets, roofs, and other impervious surfaces. This influx of water can overwhelm the capacity of the wastewater treatment plant, leading to what are known as combined sewer overflows (CSOs).

When a CSO occurs, a mixture of untreated sanitary sewage and stormwater is discharged directly into nearby rivers, lakes, or oceans. These overflows can cause significant environmental pollution, impacting water quality, harming aquatic ecosystems, and posing risks to public health. Addressing the challenges posed by combined sewers often involves strategies like separating the systems, implementing green infrastructure to manage stormwater closer to its source, and upgrading wastewater treatment facilities to handle higher volumes.