Depending on the region and the type of structure, overflow discharge at a combined sewage screening system occurs several times a year. Usually, it is assumed that a storm screen is in operation for about 1000 hours in 10 years.
Combined Wastewater Screening
Screens for solids retention at sewer overflow structures for the protection of water bodies
Structures with overflow are used to relieve the sewer system during rainfall. They either discharge the excess water/sewage/combined water directly into the receiving watercourse or initially store it temporarily. In practice, different types of structures can be found:
Stormwater overflow: As soon as the water level in the sewer rises above a maximum permissible level, wastewater is discharged into the receiving water via an overflow channel.
Stormwater overflow tank: When the rain weather begins, the wastewater is stored in a tank. When the tank storage capacity is reached, the wastewater is discharged via an overflow into the nearest watercourse. At the end of the storm event, the contents of the tank are discharged back into the sewer system and further to the wastewater treatment plant.
Stormwater retention tank: These basins are only used for temporary storage of combined sewage or wastewater and do not have an overflow into a receiving water body.
Sewer with storage capacity and overflow: Such reservoir sewers are very large sewers that can store wastewater. If the storage sewer is equipped with an overflow, it functions like a stormwater overflow basin.
Combined Water Screening with HUBER Stormwater Screens
HUBER Storm Screen ROTAMAT® RoK1 TS with a cross conveyor for high solids loads
HUBER Storm Screen ROTAMAT® RoK2 for stormwater discharges
HUBER Screening Systems
HUBER offers proven screening systems for overflow structures for all tanks, basins and sewers that discharge wastewater into a body of water.
These systems reliably retain solids from combined sewage or wastewater, and only mechanically pretreated wastewater enters the watercourse. This minimises the discharge of contaminants into the environment. The retained screenings can either be fed to the sewage treatment plant via the sewer system or discharged on site.
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FAQ
Frequently Asked Questions
In a combined sewer system, direct overflow discharge to a water body can occur several times a year. Many municipalities therefore use a storm screen to prevent coarser solids from entering the watercourse in the event of overflow discharge.
Precise knowledge of the discharged overflow volume is obtained when discharge volume measurement is used. The knowledge of the actual discharged water volumes is important information for the optimisation of the entire sewer network management.
For this purpose, volume measuring devices should be provided at overflow sills to record the combined water overflow discharged as accurately as possible. HUBER Storm Screen ROTAMAT® RoK2 used on the overflow structure can be equipped with discharge volume measurement.
If the water level exceeds a maximum permissible level, water is discharged into a nearby body of water. The discharge frequency is the number of days on which water is discharged.
The discharge duration is the time (e.g. in hours) during which wastewater is discharged over the overflow sill into the receiving water.
The better the wastewater has been treated before discharge, the less problematic a frequent and/or long-lasting discharge event is.
