Discharges from municipal
treatment plants
Nutrient discharges in Sweden increased sharply up to the 1960s
owing to the extension of municipal sewer networks. The late
1960s and ’70s therefore saw the construction of a system of
modern treatment plants for removal of phosphorus and organic
substances. A major fall in such discharges then ensued. Since the
mid-1980s, the plants have been supplemented with new removal
methods involving nitrogen reduction as well. These maps show
discharges of the substances from MWTPs, per sea basin, in 2006.
The largest quantities of nitrogen and organic substances are
discharged in the Baltic Proper basin, while phosphorus discharges
are roughly equal in the Kattegat and the Baltic Proper. Quantities
entering the Skagerrak, being small, hardly show on the figure.
The removal rate for phosphorus and the biological oxygen
demand (BOD) load has been around 95% for the past decade. For
nitrogen, the removal rate is considerably lower but has improved
during this period for the larger treatment plants with recipients
vulnerable to nitrogen. On average, for the whole of Sweden, this
rate was just under 60% in 2006.