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, 1m3 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.
Highlights
In the last decade, membrane bioreactor (MBR) have attracted a great deal of attention for the treatment of both municipal and industrial wastewater (Trouve et al, 2014), with more than 2500 MBR plants operating worldwide (Meng et al, 2012)
For the functional unit chosen in this case study, which is the effective treatment of 1 m3 of urban wastewater, the total CO2 emission equivalents (CO2-eq) emissions of the MBR pilot unit are amount to 4.65 kg CO2-eq/m3, while the contribution of each parameter of the system to the total
This especially high contribution (i.e. 97%) can be attributed to two main reasons: (i) the local energy mix, which is heavily depended on fossil fuels, and (ii) the overall low contribution to the total CO2-eq emissions of the equipment and materials used for the construction of the unit
Summary
MBRs have attracted a great deal of attention for the treatment of both municipal and industrial wastewater (Trouve et al, 2014), with more than 2500 MBR plants operating worldwide (Meng et al, 2012). The MBR technology features various distinct advantages over the conventional activated sludge (CAS) process. The occurrence of contaminants of emerging concern, including pharmaceuticals (i.e. licit and illicit drugs) and personal care products in treated wastewater and receiving waters is an issue which concerns conventional wastewater treatment. MBRs hold a promise for more efficient or even complete degradation of some microcontaminants from different water matrices, compared to the conventional biological systems; mainly due to the high sludge concentration and relative high sludge age, at which they operate (Sipma et al, 2010). According to the scientific literature, MBR has been proved to be a sufficient treatment technology for the removal of various licit and illicit drugs
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