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3. European Union, Council Directive concerning urban wastewater treatment, 91/271/EEC, Official Journal of the EC No L135/40, 30/5/1991.
4. European Commission, DG Environment, Working Document on Sludge, 3rd Draft, Brussels, 2000, Available from: http://ec.europa.eu/environment/waste/sludge/pdf/sludge _en .pdf.
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