Software tool for waste treatment selection using economic and ecological assessments

Abstract

For two reasons waste emanating from chemical production is of particular importance for chemical companies. First, waste treatment cost significantly contribute to the total production cost, and second, increasing environmental awareness urges the companies to reduce waste streams and emissions from treating them, thus reducing environmental impact. We developed a software tool that, taking an existing chemical plant as an example, for a given waste stream calculates the cheapest feasible combination of treatment operations that satisfies legal emission limits. A special feature of the software is that uncertainty in waste stream composition and separation efficiencies (e.g. in early process development phases) can be easily propagated through the model leading to probability distributions of treatment cost and selected treatment paths. This computer tool is now being extended for assessing the environmental impact of chemical waste treatment. As indicators for this assessment the method of environmental scarcity as well as eleven indicators selected by chemical industry as part of its responsible care program are used. To demonstrate its capabilities the model was applied to two made-up waste streams. The results show that rather small variations in one or several input parameters might result in pronounced differences in treatment cost because certain treatment options are unfeasible and emission limits are exceeded rendering a scenario legally non-compliant. Furthermore, possible conflicts between cost and environmental impact are demonstrated, and the major contributions with regard to environmental impact of the different steps of a treatment path are highlighted. In summary, the model supports the recognition of technical, legal, financial, and environmental problems in chemical waste treatment already at early phases of process design.