Modeling Tools for Environmental Engineers and Scientists

Now, the equations are coupled ODEs with arbitrary inputs, and again, anumerical method has to be adapted for their solution. The computer implementationof this problem using ithink ® is shown in Figure 8.10. Even thoughthis diagram can be compacted to be visually more pleasing, it is presentedwith all the details to illustrate its development.Sample plots from the trial-and-error process in the search for the optimalsplit of the volume are shown in Figure 8.11 for a fraction of the total volumein the first tank of 0.40, 0.60, and 0.80. As can be seen from these plots, whenthe first tank has a volume of 40% of the total volume, the toxicant concentrationin that tank exceeds the limit of 30 mg/L, thus resulting in inhibitionof the bioprocess and increase in effluent BOD.The final plots of toxicant and BOD concentrations in the two tanks with55% of the total volume in the first tank, when all the criteria are adequatelymet, are shown in Figure 8.12.In the ithink ® package, the modeler can build a GUI so that users can runthe model under various conditions without having to interact directly at themodeling layer. One such interface is shown in Figure 8.13 with a slider inputdevice, where users can set a volume fraction (within a range preset by themodeler) and click on the Run Model button to plot the effluent profiles fromeach tank. A useful feature of the slider is that it lets users change the valueat any time during the run, interactively, and update all calculations thereafter(however, in this example, that feature is of no practical use). Users can alsoclick on the two icons depicting the arbitrary toxicant and BOD input profilesand modify them to simulate other scenarios.Figure 8.10 Pretreatment system—ithink ® model of modified system.© 2002 by CRC Press LLC