Mischwasserkanäle

Mischwasserkanäle, also known as combined sewers, are a type of sewer system that carries both sanitary sewage and stormwater runoff in a single pipe. Historically, many older cities were built with combined sewer systems. Sanitary sewage originates from homes and businesses, including wastewater from toilets, sinks, and showers. Stormwater runoff is precipitation that falls on streets, roofs, and other impervious surfaces, collecting pollutants like oil, grease, and debris as it flows.

When it rains, the volume of water in a combined sewer system can increase dramatically. This can overwhelm the capacity of the treatment plant, leading to a condition called a combined sewer overflow (CSO). During a CSO event, a mixture of untreated sewage and stormwater is discharged directly into nearby rivers, lakes, or oceans. This pollution can harm aquatic life, impact recreational water use, and pose risks to human health.

Managing and mitigating the effects of combined sewer systems is a significant challenge for many municipalities. Strategies include building larger pipes, constructing underground storage tanks to hold excess flow during storms, and implementing green infrastructure solutions like rain gardens and permeable pavements to reduce the amount of stormwater entering the system. Separating combined sewers into distinct sanitary and storm sewer systems is another long-term solution, though it is often a costly and complex undertaking.