Nitrogen removal is now required by the Swedish parliament. The new requirements will be valid before 1995 and in some cases before 1992. A comprehensive development program, mostly in full scale at about 35 municipal sewage treatment plants, has been started to meet the new demands. In order to co-ordinate all activities, a National Nitrogen Project with representatives from authorities and municipalities has been formed.
The general ambition is to meet the demand by process development, using existing volumes rather than to invest in civil works. A Swedish concept has appeared, which in most cases has served as a guideline for the development program. The basic principles are to decrease the load on the biological process by pre-precipitation, to utilize the remaining organic content in the wastewater in a pre-denitrification system, to increase the active biomass in the biological system and to use a two-sludge system with post-denitrification.
In this paper, some experiences from the activities in Sweden are discussed and exemplified with results mainly from Falkenberg, Malmö and Norrköping. The treatment plant in Falkenberg was the first to introduce biological nitrogen removal in Sweden. A pre-denitrification system has been in operation since May 1983 with good results. Comprehensive full-scale and pilot tests are in operation at the Sjölunda and Klagshamn sewage treatment plants in Malmö. Special interests have been paid to studies on different applications of fixed film technology. The plant in Norrköping is operated with pre-precipitation followed by combined pre- and post-denitrification.
A new hybrid sewage treatment system combining a rolled pipe system and membrane bioreactor to improve the biological nitrogen removal efficiency: A pilot study