An overflow construction, placed at Kærbyholmrende, Middelfart, functions as a test and demo site for cleaning combined sewer overflow (CSO) with a HydroSeparator.

The project is a cooperation between Middelfart Wastewater and Bonnerup Consults, and is supported by the Ministry of Environment.

The HydroSeparator is developed by Bonnerup Consult primarily for treatment of rainwater, but the preliminary tests with combined sewer overflow has shown relatively good results.

With additional cleaning steps in form of chemical precipitation and further alignment with the overflow, the system can be a technically, economically and operationally attractive solution for treatment of CSO.

The HydroSeparator is based on the following cleaning steps

• Step 1: Just before the HydroSeparator the combined sewer overflow (CSO)  passes a self-cleaning screen to remove particles over 4 mm
• Step 2: Afterwards the first and most dirty part of the CSO is retained inside the HydroSeparator
• Step 3: The rest of the overflow passes through the lamellas for removal and settlement of big particles
• Step 4: Smaller particles are removed using a mesh filter
• Step 5: When the overflow situation is over, the tank, lamellas, and filters are automatically sprayed and flushed with filtered water to ensure that the system is clean and ready for the next rainfall
• Step 6: The retention tank is emptied, and the retained water is pumped back to the sewer system together with the water used for cleaning
• Step 7: During long rainfalls the combined sewer water is relatively diluted, and in these situations, an optional bypass function can be used