Environmental Assessment of Waste Treatment Process Alternatives

Diploma Thesis

O. Jankowitsch, L.Cavin, Dr. U. Fischer, Prof. K. Hungerbühler


Treating waste is a problem inherent to chemical industry. In times of enhanced environmental awareness and stricter legislation, it has become essential to include ecological aspects in process evaluations. Following the principles of integrated pro-cess design, such consideration would include the waste treatment facilities and would take place at an early planning phase, where alternatives can still be altered without too onerous repercussions. This work presents a systematic methodology to assess process alternatives for the treatment of a specified waste stream. Four indicators are computed: Energy demand, the required auxiliaries, the resulting emissions, and the recycled substances. All this figures are expressed in ecopoints according to an impact assessment performed with the method of ecological scarcity. Since all four indicators bare the same units, an aggregation is possible. Additionally, eleven parameters from the chemical industryís Responsible Care program complete the environmental evaluation. The methodology was implemented in the framework of an existing program designed to estimate costs for treating waste, discarding treatment alternatives which are legally not compliant. A Monte Carlo Simulation is performed to reflect uncertainties, resulting in a distribution of the responses rather then in single values. Eventually two targets will be available leading to a multi-objective problem. Hence a pareto - approach has been proposed, allowing to eliminate alternatives that are dominated, i.e. whose scores for both objectives are higher then other treatment paths. Various other tools for analysing the results are provided as well. Several case studies were simulated with the presented software package. Complex behaviour arose, but with the use of the different graphical tools explanations could be stipulated. The high flexibility of the software allows user specific examination strategies. Cases could be observed where trade-offs exists between the optimal ecological and economical alternatives; in other examples, straightforward decisions could be taken, the cheapest path being also the environmentally most benign.