Until 1985, one of the wastewater treatment plants in Odense, Denmark, was a traditional trickling filter plant designed for approx. 275,000 PE. To meet rigorous standards for N and P removal, the plant was extended in 1986-1988, and the extended plant was put into operation in April, 1989. Now, standards have been changed again and are : N < 8 mg/l and P < 0.5 mg/l. These standards must be complied, with before 1992.
The establishing of design criteria based on statistical methods is presented. On the basis thereof, one of various extension alternatives was chosen. This involved keeping the existing primary settling tanks and performing partial nitrification in the existing trickling filters succeeded by a new structure for N and P removal according to the BIO-DENIPHO method. The future extension for contact filtration is mentioned. Basic civil engineering data are described together with design and operating economy. Furthermore, mention is made of the commissioning procedure and the first results.