Discharge of nitrogen and phosphorus from urban wastewater treatment plants

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Over the last 20 years, marked changes have occurred in the proportion of the population connected to waste water treatment as well as in the waste water treatment technology involved.

In the northern countries, most of the population are today connected to waste water treatment plants with tertiary treatment, which efficiently removes nutrients and organic matter from the waste water. In the central EEA countries, more than half of the waste water is treated by tertiary treatment, a quarter by only biological treatment which removes most of the organic matter and the ammonia. Southern countries and the accession countries for the moment only have around half of the population connected to waste water treatment plants. Some 30 to 40 % of the population are connected to secondary or tertiary treatment.

The improvement in waste water treatment was due to implementation of the urban waste water treatment directive (see the status of implementation at later indicator) and resulted in marked lower discharge of organic matter and nutrients to water.

In the countries included in Figure 3.17, the percentage of population connected to tertiary treatment increased from 40 to 80 % during the 1990s. Over the same period, the discharge of phosphorus and nitrogen from waste water treatment decreased by 60 and 30 % respectively. This difference reflects that nearly all the tertiary treatment plants have phosphorus removal while only some of the plants, in particular the large plants, have nitrogen removal.