1. Baek, N. H. and Clesceri, N. L.: 1986, Water Res. 20, 345.
2. British Standards Institution: 1983, British Standard Code of Practice BS 6297, B.S.I., London, U.K.
3. Bundesgesundheitsam: 1982, NTA in Waschmitteln, Bundesminister für Jugend, Familie and Gesundheit, Berlin, W. Germany.
4. Department of the Environment and National Water Council: 1977, Chemical Oxygen Demand (Dichromate Value) of Polluted and Waste Waters, H.M.S.O., London, U.K.
5. Department of the Environment and National Water Council: 1981, Report of the Sub-Committee on the Disposal of Sewage Sludge to Land, N.W.C., London, U.K.