The mass of contaminants present in domestic and industrial wastewaters, in leachates, groundwaters, and in soils naturally varies with either time or space. These natural and sometimes severe variations are coupled with the uncertainties associated with direct exposure to the environment. In the face of such an unsteadystate behavior, facilities used for the removal of contaminants are often designed with the potentially unrealistic expectation that they can be operated as steady-state systems.
IRVINE, R.L. ; WILDERER, P.A. ; FLEMMING, H.C. (1997): Controlled Unsteady State Processes and Technologies. An Overview. In: Water Science and Technology: Volume 35 , 1-10. URL [Accessed: 23.03.2015]