Liitosviemärit

Liitosviemärit, also known as combined sewers, are a type of sanitary sewer system that carries both stormwater runoff and sanitary sewage in a single pipe. This design was common in many older urban areas, particularly in Europe and North America, due to its initial cost-effectiveness and simplicity during development. In a combined sewer system, wastewater from homes and businesses, along with rainwater that falls on streets and other impervious surfaces, all flows into the same network of pipes and is transported to a wastewater treatment plant.

The primary challenge with combined sewers arises during periods of heavy rainfall. When the volume of stormwater entering the system exceeds the capacity of the pipes or the treatment plant, a condition known as a combined sewer overflow (CSO) occurs. During a CSO, untreated or partially treated sewage and stormwater are discharged directly into nearby bodies of water, such as rivers, lakes, or oceans. This discharge can lead to significant pollution, impacting water quality, harming aquatic ecosystems, and posing risks to public health.

Addressing the issues associated with combined sewers often involves complex and expensive infrastructure upgrades. Solutions include separating the combined system into distinct sanitary and storm sewer networks, constructing underground storage tanks or tunnels to hold excess flow during storms for later treatment, or implementing advanced treatment technologies at the wastewater treatment plant to handle higher volumes and pollutant loads. Many municipalities are actively working to mitigate the environmental impact of their combined sewer systems through various improvement projects.