The environmental footprint of a membrane bioreactor treatment process through Life Cycle Analysis

Abstract

This study includes an environmental analysis of a membrane bioreactor (MBR), the objective being to quantitatively define the inventory of the resources consumed and estimate the emissions produced during its construction, operation and end-of-life deconstruction. The environmental analysis was done by the life cycle assessment (LCA) methodology, in order to establish with a broad perspective and in a rigorous and objective way the environmental footprint and the main environmental hotspots of the examined technology. Raw materials, equipment, transportation, energy use, as well as air- and waterborne emissions were quantified using as a functional unit, 1m(3) of urban wastewater. SimaPro 8.0.3.14 was used as the LCA analysis tool, and two impact assessment methods, i.e. IPCC 2013 version 1.00 and ReCiPe version 1.10, were employed. The main environmental hotspots of the MBR pilot unit were identified to be the following: (i) the energy demand, which is by far the most crucial parameter that affects the sustainability of the whole process, and (ii) the material of the membrane units. Overall, the MBR technology was found to be a sustainable solution for urban wastewater treatment, with the construction phase having a minimal environmental impact, compared to the operational phase. Moreover, several alternative scenarios and areas of potential improvement, such as the diversification of the electricity mix and the material of the membrane units, were examined, in order to minimize as much as possible the overall environmental footprint of this MBR system. It was shown that the energy mix can significantly affect the overall sustainability of the MBR pilot unit (i.e. up to 95% reduction of the total greenhouse gas emissions was achieved with the use of an environmentally friendly energy mix), and the contribution of the construction and operational phase to the overall environmental footprint of the system.

Life cycle assessment of solar‐driven oxidation as a polishing step of secondary‐treated urban effluents

“…Considering that the solar Fenton oxidation could be applied as a post‐treatment of a biological process, and according to the results of a previous LCA study of our team, where the biological treatment through a membrane bioreactor of the daily effluents of a Cypriot resident, was found to be 1.2% of its daily GHG emissions; the integrated treatment of these effluents (i.e. biological + solar Fenton) would amount to approx 3% of the total GHG emissions of a local resident . This is also an insignificant contribution to the overall daily CO 2 emissions per person.…”

“…It should be highlighted that comparison of the results of different LCA studies cannot be direct. This is because each study has different goals and scope definition, different equipment and impact assessment methods are used, the assumptions made are not fully equivalent, while also the energy mix and the geographical location of each study are different . However, according to the results of the study by Muñoz et al , the main environmental impact categories of the photo‐Fenton process at bench scale for the treatment of kraft mill bleaching wastewater were the 'aquatic ecotoxicity', followed by the 'photochemical ozone formation', 'abiotic resource depletion' and 'acidification' .…”

“…These 18 midpoint impact categories are: 'climate change' (CC), 'ozone depletion' (OD), 'terrestrial acidification' (TA), 'freshwater eutrophication' (FE), 'marine eutrophication' (MEP), 'human toxicity' (HT), 'photochemical oxidant formation' (POF), 'particulate matter formation' (PMF), 'terrestrial ecotoxicity' (TET), 'freshwater ecotoxicity' (FET), 'marine ecotoxicity' (MET), 'ionising radiation' (IR), 'agricultural land occupation' (ALO), 'urban land occupation' (ULO), 'natural land transformation' (NLT), 'water depletion' (WD), 'metal depletion' (MD) and 'fossil depletion' (FD); while the three endpoint impact categories are 'human health', 'resources' and 'ecosystem'. It should be highlighted that this method is able to express the results per environmental impact category and also as an aggregated single score …”

Life cycle assessment of algae‐to‐biodiesel shallow pond production systems in the Mediterranean: influence of species, pond type, by(co)‐product valorisation and electricity mix

“…Specialised equipment is used in the microalgae‐to‐biodiesel systems, which does not exist in SimaPro's proprietary LCI databases. Nonetheless, in engineering processes, the construction phase usually has a small environmental impact, compared to the operational phase, where electricity is consumed . Thus, focus was given to electricity consumption, rather than to identifing the detailed LCI of the equipment used.…”

“…fertilisers for microalgae growth and construction of infrastructure buildings) associated with the total energetic debt of 1 MJ of biodiesel . Then, ReCiPe, a robust multi‐issue LCIA method that comprises both midpoint (it examines impacts earlier in the cause‐effect chain) and endpoint (it considers environmental impact at the end of the cause‐effect chain) indicators, was used . The midpoint approach provides a robust understanding of the environmental performance of the examined system but the results are hard to communicate to the public.…”