Wastewater Minimisation Using Multiple Storage Vessels

In Chapter 6 the most generalised model for wastewater minimisation in batch plants was presented. The model is capable of simultaneously generating an optimum production schedule and a water recycle/reuse network that is concomitant with minimum wastewater generation in multipurpose batch plants. However, the mathematical formulation presented in Chapter 6 is only applicable in the presence of only 1 reusable water storage facility. The implication, therefore, is that there exist no incompatibility issues among the present contaminants. If there is interaction between or among the existing contaminants, a need for multiple storage units might prove necessary. The methodology presented in this chapter focuses on the wastewater minimisation problem where there are multiple contaminants present in a system with multiple storage options. These storage options arise from the nature of the wastewater present and the type of contaminants present in the wastewater. The first section of this chapter provides background to the methodology developed later in the chapter. In the second section the formal problem statement is given. The mathematical formulation is presented in the third section. The fourth section presents a number of illustrative examples to which the methodology was applied. The fifth section presents conclusions that can be drawn from the chapter. Worthy of mention is that the mathematical formulation as presented in this chapter is directly applicable to multiproduct rather than multipurpose batch plants.