Environmental Impact of Wastewater Treatment - A Study of Membrane Bioreactor and Iso-Disc Technologies from a Life Cycle Perspective

Abstract: This study evaluates and compares two different wastewater treatment technologies from a life cycle perspective. The evaluating technologies are Membrane Bioreactor (MBR) technology with a microfiltration membrane and Iso-Disc technology. Both technologies are gaining market share and are an important step in a wastewater treatment plant to guarantee good effluent quality of water. In this study we use the ReCiPe Midpoint (H) methodology and eleven impact categories are evaluated. Our result shows that the Iso-Disc technology has the lowest environmental impact of all eleven impact categories when production, operation and transport are compared to the MBR technology. The operation phase has the greatest impact on the environment of all categories for both technologies. The study highlights the differences in environmental impact depending on the location of the wastewater treatment plant, where the electricity mixes of Australia, Denmark and Sweden are evaluated. When the purification level of each technology is considered, the results are changed. When indirect emissions of phosphorus and nitrogen in the suspended solids of the effluent are included, the MBR technology will be the best alternative from the impact category marine eutrophication potential. This goes for all three locations, whether it is in Sweden, Australia or Denmark. The MBR technology will also be the best alternative from the impact category freshwater eutrophication potential if the plant is located in Denmark or Sweden. When the plant is located in Australia, the Iso-Disc will still be the better alternative from the impact category freshwater eutrophication potential. The result implies, that since the electricity mix have a big impact on the result, it is important to consider the location of the plant while choosing technology from an eutrophication aspect. A better purification level will not always reduce the total emissions according to eutrophication, especially if the electricity mix consists of a large share of fossil electricity and the technology is energy intensive. It is also important to include parameters such as the purification level while doing a life cycle assessment, where different wastewater treatment technologies are being compared. The reason for this is because indirect emissions linked to the purification level, were shown to have a big impact on the environment according to eutrophication.