A model for waste treatment selection and costing under uncertainty

The cost of treatment of the waste emanating from chemical production significantly contributes to the total production cost and should therefore be estimated as early as possible during process development. We developed a model that, taking the waste treatment facilities of an existing chemical plant as an example, calculates the cheapest feasible combination of treatment operations for a given waste stream that satisfies legal emission limits. A special feature of the software is that uncertainty in the waste stream composition and the separation efficiencies (e.g., in early process development phases) can easily be propagated through the model, leading to probability distributions of treatment cost and selected treatment paths. To demonstrate its capabilities, the model was applied to three waste streams. The results show that rather small variations in one or several input parameters might result in pronounced differences in treatment costs because certain treatment options become technically infeasible or emission limits are exceeded, thereby rendering a scenario legally noncompliant. The model also highlights recycling potentials and possible problems of waste streams that might best be resolved by modifying the chemical process.