Controlled unsteady state processes and technologies - An overview

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 unsteady-state 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. Variations in the mass flow rate of individual contaminants may be captured as the forcing function in models used to define them. In controlled unsteady-state systems the impact of the forcing function is intensified rather than minimized and integrated into the design by manipulating the rate functions that determine how when, and where the constituents, including the contaminants, are created and destroyed in the system. Since system layout and operation have a strong impact on the rate functions, a question that arises regarding controlled unsteady-state systems in general and the periodic operation of such systems in particular is: Can a forcing function defined by the mass now rate of natural but irregular variations in individual contaminants be modified in periodically operated, controlled unsteady-state systems in such a way that improved performance will result? Alternatively, can any system be operated in such a manner that the uncertainties associated with waste load variations are made unimportant? In this paper, descriptions are provided that show how periodically operated controlled unsteady state systems such as the Sequencing Batch Reactor (SBR) impose a diverse array of operating conditions and selective pressures and thus become versatile tools for the enrichment of specific consortia anti induction of desired metabolic pathways. Copyright (C) 1996 IAWQ.