be biodegradable either under substantially the same conditions as are used for biodegrading the edds or such that they will biodegrade at a reasonable rate when the effluent from the process reaches the river or other final environment preferably the surf actant biodegrades at least 80 and preferably 100 or close to 100 under the conditions that result in substantially complete biodegradation of the edds during the process of the invention the surfactant or surf actant mixture may be selected from materials that will sorb on to the substrate only to a very low extent suitable anionic surfactants for use in the invention include alkyl usually c 10 14 sulphates and ethoxylated alkyl sulphates both of which are generally readily biodegradable anaerobically or aerobically and linear alkyl benzene sulphonate when the biodegradation is aerobic and secondary alkane sulphonates the use of ethoxylated alkyl sulphates especially c 10 14 alkyl with 1 to 4 ethoxy groups is particularly preferred alone or in combination with other surfactants suitable non ionic surfactants which can be used in the invention are ethoxylated fatty alcohols especially c 10 14 alkyl with 7 15 ethoxy groups glucamides and alkyl polyglycosides other suitable surfactants which can be.