Heimersson, S., Svanström, M. and Peters, G.
Chemical Environmental Science, Chalmers University of Technology, Sweden
The value of life cycle assessments depends on their completeness and on how well the assessment answers the question asked. In the EU project ROUTES several case studies have been performed in order to evaluate innovative wastewater and sludge treatment scenarios against baseline scenarios, in order to understand whether the new ones perform better or worse from an environmental systems perspective and identify the hot spots in the studied systems from where the main environmental pressure originates. The performed LCA study assesses five impact categories, Global Warming Potential, Acidification Potential, Eutrophication Potential, Ozone Depletion Potential and Photochemical Ozone Creation Potential. This article discusses the relevance of the obtained results and identifies further assessments needed in order to provide a solid result.
The study shows that, at present, although a limited number of impact categories are assessed, the studied energy-demanding technologies, like sequential batch biofilm granular reactor and membrane reactor, have a worse overall environmental performance compared to baseline scenarios, and points out electrical efficiency as the main area to put focus on to decrease the overall environmental impact. It also shows that the technologies aimed at sludge quality improvement exhibit a promising environmental performance, but further assessment, including LCA method development, is needed as the studied impact categories do not model the studied system in a thorough way when it comes to comparing agricultural application of sludge and other disposal options.
Life Cycle Assessment, LCA, wastewater, sewage sludge, process development
The issue of how to dispose of the large volumes of sewage sludge generated in wastewater treatment in an economically and environmentally feasible way is much discussed. Process development of wastewater and sludge treatment processes can have four main focuses, either to increase efficiency, to reduce or stabilize the amounts of sludge that have to be disposed, to improve the quality of the sludge or to maximize the possibility to recover resources in other ways.
Process development intended to improve wastewater and sludge treatment should preferably include environmental systems analysis of the processes under study, to ensure that sub-optimisation is avoided. The EU project ROUTES – Novel processing routes for effective sewage sludge management (see Braguglia et al. (2012) for a project description) performs process development in wastewater and sludge treatment in order to improve the sludge disposal situation in Europe. Some of the studied innovative technologies are listed in Table 1, together with their primary aim. As a part of the process development, life cycle assessment (LCA) was made in order to assess the environmental performance of the treatment processes under development compared with baseline scenarios.
Wastewater and sewage sludge treatment has been assessed by LCA in numerous studies. Several studies, among them Johansson et al. (2008) and Lundin et al. (2004), focuses on the final disposal of sludge and compares alternative solutions. Others, as Peters and Rowley (2009), assess process technologies in the WWTP together with end-uses of sludge, as guidance for policy-makers. A number of studies have, as is also done in this study, investigated the potential of new treatment technologies; for treatment of sludge as done by Svanström et al. (2005) or in the waterline as done by Hospido et al. (2012). To compare new treatment routes towards reference/baseline scenarios is for example done by Larsen et al. (2010).
A first LCA was made early on in the ROUTES project in order to assess the potential environmental performance of the studied technologies combined with different final sludge disposal options: landfill, incineration or agricultural utilisation. This paper presents some of the results from this study and discusses them in relation to whether or not the performed LCA answers the questions asked by the project and if not, which challenges that will have to be addressed in order to improve the LCA.