LCA of a Membrane Bioreactor Compared to Activated Sludge System for Municipal Wastewater Treatment

Membrane bioreactor (MBR) systems are connected to several advantages compared to the conventional activated sludge (CAS) units. This work aims to the examination of the life cycle environmental impact of an MBR against a CAS unit when treating municipal wastewater with similar influent loading (BOD = 400 mg/L) and giving similar high-quality effluent (BOD < 5 mg/L). The MBR unit contained a denitrification, an aeration and a membrane tank, whereas the CAS unit included an equalization, a denitrification, a nitrification, a sedimentation, a mixing, a flocculation tank and a drum filter. Several impact categories factors were calculated by implementing the Life Cycle Assessment (LCA) methodology, including acidification potential, eutrophication potential, global warming potential (GWP), ozone depletion potential and photochemical ozone creation potential of the plants throughout their life cycle. Real data from two wastewater treatment plants were used. The research focused on two parameters which constitute the main differences between the two treatment plants: The excess sludge removal life cycle contribution—where GWP_MBR = 0.50 kg CO₂-eq*FU⁻¹ and GWP_CAS = 2.67 kg CO₂-eq*FU⁻¹ without sludge removal—and the wastewater treatment plant life cycle contribution—where GWP_MBR = 0.002 kg CO₂-eq*FU⁻¹ and GWP_CAS = 0.14 kg CO₂-eq*FU⁻¹ without land area contribution. Finally, in all the examined cases the environmental superiority of the MBR process was found.