Environmental performance of new wastewater and sludge treatment routes compared to conventional approaches

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

Can carbon fiber composites have a lower environmental impact than fiberglass?

Carbon fiber composites are increasingly used to decrease fuel consumption in the use phase of vehicles. However, due to the energy intensive production, the reduced fuel consumption may not lead to life cycle environmental savings as much as for other lightweighting materials, for example fiberglass. This study uses life cycle assessment methodology to assess how different future development routes including using bio-based raw materials, microwave technology, and recycling of composites with the recovery of fibers influence the envi- ronmental impact of both carbon fiber composites and fiberglass in vehicles. Results show that combining different development routes could lead to carbon fiber composites with a lower environmental impact than fiberglass composites in the future and that recycling of composites with recovery of fibers is the route that alone shows the greatest potential

How uncertainties are handled in LCA – focus on the wastewater and textile sectors

Life cycle assessment (LCA) relies on large data samples and includes numerous choices and assumptions. This study aimed at reviewing to what extent relevant uncertainties are communicated and considered when interpreting LCA results, looking at current practices in LCAs on wastewater and textile systems. Our review showed that uncertainties are seldom communicated or considered in relation to the conclusions of the study, despite the availability of methods for propagating uncertainties in LCAs. We discuss that uncertainties and variation should at least be qualitatively assessed, and ideally be propagated from the life cycle inventory through the impact assessment

Methodological issues in LCA of wastewater treatment combined with PHA biopolymer production

Production of polyhydroxyalkanoates (PHAs) by mixed microbial cultures utilising the organic content of wastewaters is one of the technologies studied in the EU project ROUTES. When comparing the life-cycle environmental impacts of simultaneous wastewater treatment and production of PHA-rich biomass to traditional wastewater and solids treatment, the handling of this multi-functionality is critical for the results. Only one LCA of such a system has been found in the literature. The current paper identifies substitution and allocation based on chemical oxygen demand removal as two possible options to account for the multi-functionality of the system. Examples based on literature data were used to show that for global warming potential, the choice of allocation method can substantially affect the results

Generating LCA partitioning factors for sewage sludge management using a Delphi procedure

In attributional life cycle assessment (ALCA), the goal is to map the environmental impact from the system under study in such a way that it reveals what share of the total global environmental impact that belongs to the product or service investigated. Any process performing multiple functions then gives rise to an allocation problem. It has been recommended that the partitioning in ALCA studies should be based on the drivers of the system. Wastewater collection and treatment facilities are increasingly exploited in different resource recovery attempts and therefore increasingly result in allocation problems. The drivers of present wastewater and sludge management systems is a mix of various ideas and concerns relating to environmental protection, resource recovery, economy, and other interests, that seem to vary among stakeholders, over time and across regions. We developed a two-stage Delphi procedure for finding partitioning factors for use in ALCA studies where multiple drivers and stakeholders are present in relation to multifunctional systems and tested it for a wastewater and sludge management system. The paper reports on the method, on the experiences from applying the method and implications for ALCA studies

LCA on wastewater and sludge management for local decision-making in Gothenburg – are new LCA method developments enough?

This paper describes an LCA study that was made to inform decision-makers in Gothenburg about two different sludge management options. Incineration of anaerobically digested sludge with recovery of a phosphorus fertiliser product seemed preferable to using pasteurised anaerobically digested sludge in agriculture. Aspects under the control of the decision-makers were important for overall results, and caused the main differences between the studied systems, indicating considerable potential for local improvement efforts. Applying a human toxicity characterisation method with a more sludge specific fate model were important, but not crucial, for the results. However, the results are connected to large uncertainties and remaining challenges are discussed in the paper

Including Pathogen Risk in Life Cycle Assessment of Wastewater Management. 1. Estimating the Burden of Disease Associated with Pathogens

The environmental performance of wastewater and sewage sludge management is commonly assessed using life cycle assessment (LCA), whereas pathogen risk is evaluated with quantitative microbial risk assessment (QMRA). This study explored the application of QMRA methodology with intent to include pathogen risk in LCA and facilitate a comparison with other potential impacts on human health considered in LCA. Pathogen risk was estimated for a model wastewater treatment system (WWTS) located in an industrialized country and consisting of primary, secondary, and tertiary wastewater treatment, anaerobic sludge digestion, and land application of sewage sludge. The estimation was based on eight previous QMRA studies as well as parameter values taken from the literature. A total pathogen risk (expressed as burden of disease) on the order of 0.2–9 disability-adjusted life years (DALY) per year of operation was estimated for the model WWTS serving 28 600 persons and for the pathogens and exposure pathways included in this study. The comparison of pathogen risk with other potential impacts on human health considered in LCA is detailed in part 2 of this article series

Improved life cycle assessment of wastewater and sludge management with resource recovery

Around the world every day, large amounts of wastewater are treated before release, to avoid impacts on humans and the environment. The treatment requires resources in the form of energy and chemicals, and it generates large amounts of sewage sludge, however, it can also serve as a source of energy, nutrients and carbon. These valuable resources can be recovered in many ways, including in the form of biogas, or through the use of sludge in agriculture or even, potentially, in form of biopolymer raw material.Life cycle assessment (LCA) can be used to quantify the life cycle impact of wastewater and sludge management with resource recovery, on humans and the environment, in order to evaluate their environmental performance and avoid sub-optimisation. LCAs of such systems face different types of methodological problems. This thesis focusses on two such problems.The first research topic concerns how to divide the environmental impact that results from a wastewater treatment process with the simultaneous production of a valuable by-product. Methodologies exist for handling such general situations, however, some properties inherent to wastewater and sludge management may result in complex allocation problems. This research identified the LCA of a system with wastewater treatment and simultaneous polyhydroxyalcanoate (PHA) production as particularly challenging, if PHA was considered as the main product. Three partly new allocation approaches were evaluated, and the choice of approach was found to influence the LCA results.A second research topic concerns the potential importance of assessing the risks of the pathogens that exist in wastewater and sludge management systems, which is not currently done within the LCA framework. This research has found that these risks are potentially important compared to other impacts on human health, both for wastewater and sludge management systems where sludge is incinerated or used for agricultural purposes

Improved methods and practices in life cycle assessment of wastewater and sludge management

Large amounts of municipal and industrial wastewater are treated each year in order to prevent negative consequences to human health and the environment. The treatment processes, directly or indirectly, give rise to environmental impact, but also offer several possibilities to recover resources.The research presented in this thesis is aimed at improving the relevance of Life Cycle Assessments (LCAs) for the evaluation of the environmental performance of wastewater and sludge management systems, e.g., for process development purposes, or to provide guidance in decision-making on sludge management alternatives.A review of previous studies within the area show that the data inventory practice differs, in terms of which emission and recoverable flows are included and how these flows are quantified, which may have a large influence on results. The review is intended to serve as guidance for future life cycle inventory practice.One area of focus of this research has been systems in which sludge is used in agriculture, partly as this is an issue that attracts stakeholder concern. It was shown that pathogen risk, which historically has not been assessed within the LCA framework, may constitute an important contribution to the overall impact on the endpoint human health. Another important contributor was human toxicity potential. The uncertainties when assessing human toxicity was, however, shown to be high for this type of systems when using currently available assessment methodology, mainly due to uncertainties in the characterisation of heavy metals. Applying a characterisation method adjusted to be more specific for exposure through sludge applied in agriculture did not influence results much. The way resource utilisation from sludge as organic fertiliser is accounted for in LCA studies was also evaluated, and a novel approach to account for the potential benefits of the provision of organic matter to arable land (in addition to the benefits of nutrient provision) was suggested and evaluated. Another focus area has been how to allocate impacts between the different functions provided in a system with simultaneous wastewater treatment and generation of PHA. A novel basis for comparison of the functions was suggested and evaluated, and was shown to be useful