Modeling Tools for Environmental Engineers and Scientists

in the Input column. In this example, a Guess value was input for the unknownL. On completion of the iteration process, TK Solver returns the correctanswer for L in the Output column.8.7 MODELING EXAMPLE: WASTE MANAGEMENTIn this example, a simple model is developed for multipurpose use in ametal plating facility. The objective of the model is to simulate the facilityunder various scenarios for use in process analysis, product selection, materialbalances, record keeping, optimization, waste minimization studies, life cycleanalysis, etc. The processes to be included are paint formulation, spray paintingoff-gas treatment, and recovery of solvents. The model is based on simplematerial balances using average flows and capacities. The following factorsare to be determined for each scenario examined: the best alkyd:epoxy:thinnerproportion, the volumes of the three components consumed per year (gal/yr),the concentration (ppmv) of toluene in the off-gases from the painting operation,the amount of toluene (lbs/yr) that can be recovered by using the carbonadsorption system, the concentration (ppmv) of toluene in the off-gases aftertreatment by activated carbon, the atmospheric emissions (lbs/day) of tolueneafter installing the activated carbon system, the concentration (mg/L) oftoluene in the condensate, and the energy (KW) requirement for the activatedcarbon system.Because the model is expected to simulate the system under average conditions,a steady state model would be adequate, and as such, the Excel ®spreadsheet package is chosen in this case. The spreadsheet model is builtwith a graphic interface as shown in Figure 8.27. The model parameters arereadily accessible for any changes to be made for evaluation. The appropriateMB equations are embedded in the cells to calculate the model outputs. Itshould be noted that the spreadsheet is built from “top-down,” and specificparameters must be known in advance so that the model can run through thecalculations using the known data and calculating the unknowns.8.8 MODELING EXAMPLE: ACTIVATEDCARBON TREATMENTPowdered activated carbon (PAC) is a commonly used adsorbent for treatinga wide range of wastewater. In this example, use of PAC in treating a dyebath effluent is modeled to evaluate alternative process configurations. In anexisting process, the effluent is contacted with PAC in a CMFR to removecolor, and the PAC is recycled after off-line biological regeneration. Theprocess was designed based on the experimental observation that interparticle© 2002 by CRC Press LLC