Figure 8: Source and sink CC for SK1+SK3 in contaminant cascade ’A’ (a) Before shifting source CC for SK3 (b) After shifting source CC for SK3
The step is repeated again for the sinks that are in contaminant cascade ’B’. The source ranking order based on contaminant ’B’ is SR4->SR3->SR2->SR1. The design first starts with SK2. If the sources are allocated based solely on prioritisation of SR4, the Pinch occurs at contaminant ’A’ (see Figure 9a). This is not optimal as SR3 can still be allocated due to the limit for contaminant ’B’ is not reached. The flowrate of SR4 is then reduced, and SR3 is used until both contaminants have Pinches (see Figure 9b). The identical scenario is observed for SK4 (Figures 11c and d). Notice that in Figure 9d, a triangle is formed around the source and sink CC for contaminant ’A’. This is feasible as the final load of contaminant ’A’ for SK4 is still satisfied.
The Composite Curves show exactly the sources to be allocated for each sink. This is because the freshwater target and the Pinch are determined sequentially for each sink. By doing this, the simultaneous target and source allocation for each sink can be obtained. The allocation of sources is directly connected to the network design as well. The detailed illustration of the source allocation to the sinks is shown in Figure 10.