Urban waste water treatment

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Over the last twenty years, marked changes have occurred in the proportion of the population connected to wastewater treatment as well as in the wastewater treatment technology involved. In northern countries most of the population are today connected to wastewater treatment plants with tertiary treatment, which efficiently removes nutrients (nitrogen or phosphorus or both) and organic matter from the wastewater. In the central Europe countries more than half of the wastewater is treated by tertiary treatment. Southern countries and the Accession countries only have around half of the population connected to wastewater treatment plants at the moment. 30 to 40 % of the population are connected to secondary or tertiary treatment. These changes have resulted in improvement of the state of water bodies with a decrease in concentration of orthophosphates, total ammonium and organic matter over the past ten years. For nitrate however no clear trend can be found at a national level though at the monitoring station level a decrease in concentration can be found at some stations. In the EU these decreases are linked with the implementation of European legislation. In the Accession Countries decreases are due to the general increase in the level and extent of waste water treatment and because of the recession associated with the transition to market-oriented economies (see WEU2). The increase in the proportion of the population connected to waste water treatment, as well as in the level of treatment, leads in turn to an increase in the quantities of sewage sludge produced. This sludge has to be disposed of, mainly through spreading on soils, to landfills or by incineration: these disposal routes can transfer pollution from water to soil or air.