Sewers

The term wastewater refers to water that has been altered by its use in households, craft, commercial and agricultural activities (domestic wastewater), as well as rainwater from impermeable surfaces. Wastewater must be discharged from inhabited areas and treated appropriately in a wastewater treatment plant. It is transported via the sewerage system, an underground network of pipes that discharges wastewater in a controlled manner from urban areas.

There are two basic types of sewer systems: combined sewer systems and separate sewer systems.

In a combined sewer system, domestic wastewater and rainwater are collected together in the same pipe and transported to the treatment plant. In order to relieve the network and the treatment plant during heavy rainfall, the system is equipped with overflow structures that allow excess, highly diluted water to be discharged into the receiving environment. When significant differences in level must be overcome on the way to the treatment plant, pumping stations are used.

In a separate system, however, domestic wastewater and rainwater are collected separately. Wastewater is conveyed to the treatment plant, while rainwater is conveyed to the watercourse via a separate system. Rainwater retention basins are used to temporarily store rainwater and regulate its flow during periods of heavy rainfall.

The sewer network thus ensures continuous and hygienic disposal of wastewater, while protecting against flooding and environmental damage caused by uncontrolled runoff.

In Luxembourg, the combined sewer system is still the most common type. However, in the cities of Luxembourg and Esch-sur-Alzette, a significant proportion of separate sewer systems are already in place. New agglomerations are, in principle, systematically equipped with a separate sewer system. Particular attention must therefore be paid to avoiding incorrect connections, as the erroneous introduction of domestic wastewater into the storm sewer system would place a significant burden on watercourses. Given that the existing network is mainly designed as a combined system, wastewater is often reintroduced into this network and then eventually reaches the treatment plant via the discharge structures.

Regular camera inspections are used to check the condition of the pipes in order to ensure they are working properly and to detect any leaks at an early stage. Damage can be caused by root penetration, among other things. Blockages due to the improper disposal of waste in the sewer system are also a frequent problem, which everyone can help to remedy by behaving responsibly.

When rehabilitation is necessary, different processes are used depending on the type of damage, such as lining, the use of robotic techniques or open trench work. The size of the pipes is determined based on the expected flow rates.