DAF unit for municipal wastewater treatment plant


The city of Ajaccio at Corsica is operating with large fluctuations in the influent of their municipal wastewater treatment plant. During the holiday season the quantity of wastewater to the municipality is significantly higher than in the rest of the year. The design of the new biological treatment system at this municipality has to operate with these variable flows during all seasons in a year. A biological treatment system based on MBBR technology is selected. MBBR stands for Moving Bed Bio(film) Reactor

In an MBBR the bacteria are growing on plastic carriers that are kept in suspension by the aeration system of the biological treatment process. The MBBR system has some specific advantages:
  • Small footprint.
  • Adaptable to changing loads.
  • Stable for flow variations

The effluent quality after a typical well designed MBBR is in accordance with the European Regulations, except for the amount of suspended solids.

System design
In cooperation with the main contractor for the project, Vinci Environment from Paris, Nijhuis Water Technology designed two dissolved air flotation systems to remove the suspended solids from the MBBR effluent. The polished effluent quality is within the required discharge levels.

Nijhuis Water Technology supplied two units type NPF 600 HX. These high rate flotation units are equipped with a special designed discharge valve and can handle the large flow variations of 50 to 815 m3/hr for each unit. The two dissolved air flotation units are reducing the total suspended solids amount from 100 – 350 mg/l down to less than 20 mg/l.

Special features

The special designed high rate flotation units show a footprint of only 35 m3 each, which is unique. These units can handle large flows on a relatively small footprint and due to the effluent discharge system variations in the flow can be handled easily.