An operating tale from næstved sewage treatment plant
Conversion from a two-stage to a one -stage plant
Næstved Central Sewage Treatment Plant was built as a Bio DeNiPho plant to treat 89,000 PE and the load is about 45,000 PE.
The results of analyses of the micro pollutants indicated already in 1998 that we would face problems with export to the agriculture segment after 1 July 2000. At the same time the industry started saying that the micro pollutants could not be reduced in a digester whereas a reduction could be expected in an aerobe process. Næstved Municipal Authority decided to convert the plant into a one-stage plant. The objective was:
- To achieve the lowest possible content of micro pollutants in the sludge
- To reduce the total amount of sludge exported to agriculture.
As will be seen from the graphs below the conversion has met expectations with regard to reducing the content of micro pollutants.
Unfortunately we did not have the same degree of success with regard to a reduction in sludge volumes. The reason proved to be poor dewatering properties caused by the bacteria Microthrix Parcvicella. This problem was solved in association with Kemira Miljø A/S.