LCA Case Studies Preliminary Assessment of the Environmental Benefits of Enzyme Bleaching for Pulp and Paper Making
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Goal and Background. The LCA methodology is used to compare the potential environmental benefits of an emerging biotechnology, enzyme-bleaching, with those of elemental chlorine free (ECF) bleaching, an existing technology that is widely used in paper making. Through the use of biodegradable enzymes to supplement, or eventually to replace, chemicals in the bleaching process to extract lignin, enzyme bleaching processes are aimed to reduce the use of chlorine based bleaching chemicals and to achieve cost savings by circumventing investment into oxygen delignification or ozone bleaching technology. Scope and Method. The assessment is conducted using SimaPro 4.0 and focuses on the processes within the bleach plant stage. For this study, ECF is replaced by enzyme bleaching only in the first stage of the bleaching process. Because this is a comparative study, all upstream and downstream processes are excluded. The impact categories based on Eco-indicator 95 are used to characterize the inventory data in this study. Other methodologies, such as Eco-indicator 99 and CML 2000, have not been chosen as they are more region-specific and are not yet fully applicable to the Canadian environmental condition. A new initiative to develop a Canadian Life Cycle Impact Assessment (LCIA) Method is ongoing at the Interuniversity Reference Center for the Life Cycle Assessment, Interpretation and Management of Products, Processes and Services (CIRAIG), Ecole Polytechnique, Canada. Results and Conclusion. The analysis shows that the introduction of enzyme bleaching into the ECF process significantly improves the overall environmental performance in the majority of the impact categories. Extending the substitution of enzyme bleaching for chlorine dioxide is warranted. Of the three impact categories where increased impact was noted, two of these which increased emissions of greenhouse gases and increased incidence of summer smog, would be completely eliminated if the enzyme mediator was manufactured at the point of use. There remains a potential for increased impact from eutrophication, which would need to be managed. Recommendations and Outlook. With the only partial substitution of ECF by enzyme bleaching examined here, chlorine dioxide consumption, energy consumption, NaOH consumption, and transportation remain the key hot spots and warrant further research. Anything that can be done to replace or reduce chlorine dioxide consumption will benefit the environment.