1. Council Directive 91/271/EEC of 21 May 1991 Concerning Urban Waste Water Treatment, The Council of the European Communities.
2. Commission Directive 98/15/EEC of 27 February 1998 Amending Council Directive 91/271/EEC with Respect to Certain Requirements Established in Annex I, The Commission of the European Communities.
3. Workshop on Problems Around Sludge. Proceedings;Magoarou,2000
4. L. Bontoux, M. Vega, D. Papameletiou, Urban wastewater treatment in Europe: what about the sludge? IPTS Report, April 1998, p. 5.
5. Danish Ministerial Order. No. 823, Application of waste products for agricultural purposes, September 16, 1996.