The values of change (increase/or decrease) in discharged load between 1990 and 2009 (expressed in percentages, where values in 1990 = 100%) are plotted against the values of change in population growth.

Absolute decoupling occurs when the environmentally relevant variable is stable or decreasing while the driving force is growing. Relative decoupling occurs when the growth rate of the emission is positive, but less than the population growth rate.

]]>**N _{tot}discharged= N_{tot}(coll.system)+N_{tot}(without treatment)+ N_{tot}(IAS)+N_{tot} (primary)+ N_{tot}(secondary)+ N_{tot}(tertiary)**

Where N_{tot}discharged is a total annual nitrogen load discharged from collecting systems or wastewater treatment plants [kg/y]

N_{tot}(coll.system) is a total annual nitrogen load discharged from collecting systems without treatment [kg/y]

N_{tot} (primary) is a total annual nitrogen load discharged from wastewater treatment plants with primary treatment [kg/y]

N_{tot}(secondary) is a total annual nitrogen load discharged from wastewater treatment plants with secondary treatment [kg/y]

N_{tot}(tertiary) is a total annual nitrogen load discharged from wastewater treatment plants with tertiary treatment (N, P removal) [kg/y]

For calculation of the N_{tot}(coll.system) and **N _{tot}(without treatment)** the population equivalent for nitrogen and phosphorus was used. For calculation of the

Two approaches were used to calculate nutrient discharged loads (**N _{tot}discharged and P_{tot}discharged)** of the domestic sector:

- The "default” approach is based on the percent values of the population connected to different types of waste water treatment (Based on Eurostat Water Statistics), and the default values of nutrient population equivalent and removal efficiency per type of treatment (primary, secondary, and tertiary).

p.e. for Nitrogen= 12 g/d

p.e. for Phosphorus=2,5 g/d

Removal efficiency :

Nitrogen (primary)=0,15

Nitrogen (secondary)=0,35

Nitrogen (tertiary)=0,70

Phosphorus (primary)=0,10

Phosphorus (secondary)=0,20

Phosphorus (tertiary)=0,80

- A second approach was used to illustrate the actual emissions from urban treatment plants based on data reported voluntarily by 13 Member States (BE, CY, CZ, DE, DK, EE, ES, IT, LT, LU, LV, NO, SI) under the UWWTD (2011 data request). Complete datasets on the emission load discharged from treatment plants (size ≥2000 p.e) were available for AT, NL, CZ, DE, DK, LT, LU and SI.

For these eight countries, the total discharged load was calculated according to the following formula:

**N _{tot}discharged= N_{tot}(WWTPs) + N_{tot}(coll.system)+N_{tot}(without treatment)+ N_{tot}(IAS)**

Where **N _{tot}(WWTPs)** corresponds to the sum of discharged loads reported under the UWWTD for individual treatment plants normalised by overall entering load in population equivalent (to make adjustment for industrial share in the load entering into urban waste water treatment plants) and finally multiplied by the total population connected to UWWTPs.

Calculation of **N _{tot}(coll.system), N_{tot}(without treatment) and N_{tot}(IAS) **is explained above.

For the remaining five Member States, the gap analysis was done. Where gaps (missing data on discharged load) did not exceed 30% of the total entering load (EE, NO), data gap filling was done, with emission load values calculated (for each type of treatment) from the formulae specified below. The formulae were derived from the 13 Member State emission load datasets (for UWWTPs > 2000 p.e.) .

The formulae used for calculation of the N_{tot} and P_{tot} (primary), N_{tot }and P_{tot} (secondary), N_{tot }and P_{tot} (tertiary) express the annual nutrient load discharged as a function of the reported entering load the treatment plant, (L) [p.e].

The units for the emission factors listed below are kg/y per population equivalent entering load and the emissions include the proportions from households, services as well as connected industry.

N_{tot}(primary)= 0,004*L

N_{tot(}secondary)=0,0012*L+1,213

N_{tot}(tertiary)=0,0014*L, for tertiary treatment with N removal

N_{tot}(tertiary)=0,0009*L+9,43318, for tertiary treatment with P removal

N_{tot}(tertiary)=0,0008*L , for tertiary treatment with N and P removal

A similar approach was applied to the calculation of the total phosphorus discharged load.

P_{tot} (primary)= 0,00009*L

P_{tot}(secondary)=0,0002*L+0,1373

P_{tot}(tertiary)= 0,0001*L+1,1658, for tertiary treatment with N removal

P_{tot}(tertiary)=0,0001*L, for tertiary treatment with P removal

P_{tot}(tertiary)=0,00005*L+0,4182, for tertiary treatment with N and P removal

]]>

The consequences of economic activities with regard to water quality and quantity have been analysed under the WFD in the River Basin Management Plans. Research on the link between water status (quality and quantity), relevant pressures and their economic driving forces provides an important basis for decision making and the prioritisation of measures with regard to achieving the objectives of the WFD. Moreover, it can help to indicate whether the particular driver is decoupled from its environmental impact. Easily understandable indicators will be necessary to provide signals and measure progress in improving resource efficiency.

The emission of nutrients from wastewater treatment plants provides an indication of potential water pollution. Human activity - the driver - is, in this indicator, represented by population size.

]]>]]>

The achievements through the UWWTD have to be seen as an integrated part of objectives under the Water Framework Directive (WFD), which aim at a good ecological and chemical status for all waters by 2015. That means that more stringent emission targets may be set in case it is needed for achieving the good status.

EU wide targets related to the nutrient emission intensity of domestic sectors, or the decoupling of nutrient emission from population growth have not been set.

]]>