INTEGRATION AV VÅTMARK I ETT MODERNISERAT AVLOPPSRENINGSVERK, MÖJLIGHETER OCH BEGRÄNSNINGAR / Integration of a constructed wetland with an upgraded treatment plant, perspectives and limitations
Nynäshamn community has upgraded the main wastewater treatment plant by adding an activated sludge stage, in order to handle septic sludge emanating from the southern suburban area of Stockholm. The upgraded plant was taken into operation in 2003.
The plant was earlier based on a treatment chain containing pre-treatment, chemical precipitation and a constructed wetland. The treatment objectives, set as BOD7 < 15 ppm; total P < 0,5 ppm and total N < 15 ppm were maintained with the exception for the nitrogen removal.
By the Introduction of an activated sludge facility, based on a four unit SBR-system, some distinct improvements have been identified:
The discharge levels at the plant have been typically as follows: BOD7 < 5 ppm; COD < 35 ppm; SS < 5 ppm; total P < 0.1 ppm and total N < 7 ppm
Other noticeable changes in the operation of the plant have been as follows:
• A substantial reduction of the precipitation agent for P-removal;
• The earlier frequent odours from the wetland have vanished;
• The wetland is now operated even during winter, as compared with the regular stop of 2 to 4.5 months per year.