yhdysviemärillä

Yhdysviemäri refers to a combined sewer system. In such a system, both sanitary sewage from households and businesses, and stormwater runoff from streets, roofs, and other impervious surfaces are collected and transported in the same pipe. This contrasts with separate sewer systems, where sanitary sewage and stormwater are carried in distinct pipelines.

Combined sewer systems were common in many older cities, particularly in Europe and North America, due to their historical development. The logic behind them was to simplify the infrastructure by using a single set of pipes for all wastewater. However, this design presents significant challenges, especially during periods of heavy rainfall.

When the volume of combined sewage and stormwater exceeds the capacity of the treatment plant or the sewer pipes themselves, an overflow occurs. This combined sewer overflow (CSO) typically discharges untreated or partially treated sewage and stormwater directly into nearby bodies of water, such as rivers, lakes, and oceans. CSOs can introduce pollutants like bacteria, viruses, nutrients, heavy metals, and debris into aquatic environments, impacting water quality, harming aquatic life, and posing risks to public health.

Managing CSOs is a major environmental concern for municipalities with combined sewer systems. Solutions often involve upgrading wastewater treatment plants, constructing large storage tunnels or tanks to hold excess flow during storms, or implementing green infrastructure practices to reduce stormwater runoff entering the combined system. These measures aim to mitigate the environmental impact and improve the reliability of wastewater management.