In 1993 the Norwegian Pollution Control Authorities instructed Nordre Follo WWTP to reduce their effluent discharge of nitrogen, BOD and phosphorus.
The new effluent requirements were as follows:
Phosphorus: 90% removal (annual average)
Maximum - 0.6 mg/L
Average - 0.3 mg/L
Nitrogen: 70% removal (annual average)
BOD: 90% removal (annual average)
In addition to the challenges above, it had to be a covered plant. In part because it is a tradition in Norway to provide a good working environment for the operators i.e. eliminating annoying odours, noise and aerosols.
In January 1996 AnoxKaldnes was contracted to build a wastewater treatment system for the municipality with a load equating to a population of 40,000 inhabitants.
The site’s original system consisted of primary treatment followed by coagulation, flocculation and flotation. A pilot plant was conducted by AnoxKaldnes in the early 1990’s. Results from this pilot study were used to confirm the overall design for the biological treatment system.
To fulfill the effluent requirements at Nordre Follo the Kaldnes MBBR process was designed to combine both pre- and post-denitrification. The biological treatment is followed by chemical precipitation for phosphorous removal.