Multiple storage vessel

Wastewater Minimisation Using Multiple Storage Vessels... 

The model is derived to take into consideration the possibility of multiple storage vessels which are dedicated to the storage of certain wastewater. The formulation shares some of the characteristics of the multiple contaminant model presented in the previous chapter. This is due to the fact that both formulations have roots in the scheduling methodology derived by Majozi and Zhu (2001). Furthermore, the uneven discretization of the time horizon is used as the time representation. 

Fig. 7.1 Superstructure for multiple storage vessel formulation (Gouws and Majozi, 2008)...

As with the multiple contaminant wastewater minimisation model, the mathematical model for multiple storage vessels comprises of two modules, namely, a mass balance module and a scheduling module. The constraints that comprise the mass balance module are described first. 

The constraints described above complete the mathematical formulation for wastewater minimisation using multiple storage vessels. The application of the formulation to various illustrative examples is described below. 

Illustrative Examples for the Multiple Storage Vessel Model... 

Three illustrative examples are presented to demonstrate the application and effectiveness of the proposed multiple storage vessel methodology. Each example deals with a different case of multiple contaminant problem, which will become apparent in the description of each. 

Fig. 7.2 Resulting schedule for the first example using multiple storage vessels (Gouws and...

Table 7.4 Cost data for the second multiple storage vessel example...

The binary variable dimension is further increased in the above formulations due to the fact that the binary variables describing direct and indirect reuse all carry state information, i.e., information on the state present in the water. For example, in the previous methodologies, the multiple contaminant and multiple storage vessels, there are j x j x p binary variables for direct recycle/reuse. However, in the zero effluent methodology there are, sm x j x j x p binary variables for direct recycle/ reuse. 

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