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Indicator Specification
In order to restore receiving waters to their former state, both point and diffuse pollution sources need to be further reduced. Reducing pollutant discharges from municipal and industrial WWTPs remains a central element in decoupling pressures on the aquatic environment from human activity (urban development). This is particularly true for nitrogen and phosphorus, which cause the eutrophication of freshwater and marine ecosystems. Results from large inland and marine catchments show that municipal wastewater constitutes about 75% of the point source discharges of both nitrogen and phosphorus. as a result of implementation of the Urban Waste Water Treatment Directive (UWWTD), the majority of wastewater plants in northern and central Europe now apply tertiary treatment. Elsewhere in the EU, particularly in the south-east, the proportion of primary and secondary treatment is higher. While considerable progress has been made in implementing the UWWTD, full compliance is yet to be achieved, especially in the new Member States.
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.
This indicator is used to illustrate the emission intensity of the domestic sector (household plus services), expressed as the amount of discharged pollutant from wastewater treatment/or discharged without treatment per inhabitant per year. Furthermore, the indicator shows a decoupling of the emission of nutrients (nitrogen and phosphorus) and population growth across Europe.
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.
Emission intensity is expressed in kilogrammes of pollutant per inhabitant per year. Changes in pollutant emissions from households between 1990 and 2009 are expressed in percent, where the values recorded in 1990 represent 100%. Changes in population between 1990 and 2009 are expressed in percent, where the values recorded in 1990 represent 100%.
In March 2010, the European Commission issued ‘Europe 2020 strategy’ - the European Strategy for smart, sustainable and inclusive growth. It highlights – among other things - the need for a more resource efficient economy. The “Flagship initiative” under the Europe 2020 strategy, called “A resource efficient Europe”, establishes resource efficiency as the guiding principle for EU policies on energy, transport, climate change, industry, commodities, agriculture, fisheries, biodiversity and regional development. The Roadmap to a Resource Efficient Europe defines medium- and long-term objectives to achieve efficient resource use in the region. Decoupling, in the sense of breaking the link between economic growth and resource use, is a central concept of the strategy for making Europe resource efficient. The 2050 vision and the objectives for 2020 are to be addressed in the sector initiatives that shall contribute to the resource-efficient Europe Flagship Initiative (i.e. the 7th EU Environmental Action Programme or the revision of the Common Agriculture Policy, Water Framework Directive and Groundwater Directive).
The Urban Waste Water Treatment Directive (UWWTD; 91/271/EEC) aims to protect the environment from the adverse effects of urban wastewater discharges. It prescribes the level of treatment required before discharge and has to be fully implemented in the EU-15 countries by 2005 and in the ten new Member States by 2008 - 2015. The directive requires Member States to provide all agglomerations of more than 2 000 population equivalent with collecting systems, and all wastewaters collected to be provided with appropriate treatment by 2005. Secondary treatment (i.e. biological treatment) must be provided for all agglomerations of more than 2 000 population equivalent that discharge into fresh waters, while more advanced treatment (tertiary treatment) is required for discharges into sensitive areas.
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.
For overall emission load the following formula was used:
Ntotdischarged= Ntot(coll.system)+Ntot(without treatment)+ Ntot(IAS)+Ntot (primary)+ Ntot(secondary)+ Ntot(tertiary)
Where Ntotdischarged is a total annual nitrogen load discharged from collecting systems or wastewater treatment plants [kg/y]
Ntot(coll.system) is a total annual nitrogen load discharged from collecting systems without treatment [kg/y]
Ntot (primary) is a total annual nitrogen load discharged from wastewater treatment plants with primary treatment [kg/y]
Ntot(secondary) is a total annual nitrogen load discharged from wastewater treatment plants with secondary treatment [kg/y]
Ntot(tertiary) is a total annual nitrogen load discharged from wastewater treatment plants with tertiary treatment (N, P removal) [kg/y]
For calculation of the Ntot(coll.system) and Ntot(without treatment) the population equivalent for nitrogen and phosphorus was used. For calculation of the Ntot(IAS), removal efficiencies, corresponding to the primary treatment were applied.
Two approaches were used to calculate nutrient discharged loads (Ntotdischarged and Ptotdischarged) of the domestic sector:
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
For these eight countries, the total discharged load was calculated according to the following formula:
Ntotdischarged= Ntot(WWTPs) + Ntot(coll.system)+Ntot(without treatment)+ Ntot(IAS)
Where Ntot(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 Ntot(coll.system), Ntot(without treatment) and Ntot(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 Ntot and Ptot (primary), Ntot and Ptot (secondary), Ntot and Ptot (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.
Ntot(primary)= 0,004*L
Ntot(secondary)=0,0012*L+1,213
Ntot(tertiary)=0,0014*L, for tertiary treatment with N removal
Ntot(tertiary)=0,0009*L+9,43318, for tertiary treatment with P removal
Ntot(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.
Ptot (primary)= 0,00009*L
Ptot(secondary)=0,0002*L+0,1373
Ptot(tertiary)= 0,0001*L+1,1658, for tertiary treatment with N removal
Ptot(tertiary)=0,0001*L, for tertiary treatment with P removal
Ptot(tertiary)=0,00005*L+0,4182, for tertiary treatment with N and P removal
See the alternative approach (above) based on formulae derived from available emission load data in the UWWTD Waterbase .
No methodology references available.
No uncertainty has been specified
Work specified here requires to be completed within 1 year from now.
No resource needs have been specified
No resource needs have been specified
Work specified here will require more than 1 year (from now) to be completed.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/emission-intensity-of-domestic-sector or scan the QR code.
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