The invention concerns a method characterised in that it consists in: determining online at least an ultraviolet spectrum portion of at least one of the compounds present in one or the other of the waste water feeding circuits (7, 13) or of the column (8) waste water output (16); qualitatively and quantitatively determining, by mathematical processing of the measured intensity levels, at least a contaminant present in the samples; on the basis of the results obtained and by comparing with pre-defined setpoint values, in restoring said data in the form of electric signals, which control the waste water supply and the stripping column water vapour flow rates.