Life cycle assessment (LCA) for evaluation and comparison of sewage sludge treatment options; The aim of this work package is to examine and quantify the environmental impacts of different sewage sludge treatment options using state-of-the-art LCA methodologies. The LCA will be used to assess all the novel solutions proposed in the BioTEnMaRe but special emphasis will be put on assessing the choice among different alternative ways of anaerobic digestion, composting and incineration. This choice seems to be very important for the “carbon footprint” of the wastewater treatment.
- Organic waste generation in Poland and Norway is steadily increasing, with highly different treatment practices
- Multiple technologies are available, and technology choices depend on local conditions
- Results from LCA studies are often difficult to compare due to a vast variety of assumptions, such as differences in organic waste value chain, waste composition, cut-off criteria, system boundaries, etc.
- The Organic Waste Substrate Treatment Tool (OWSTT) developed in the project helps to minimize such varieties and allows for increased flexibility and data transparency when comparing technologies and scenarios, drawing upon the methods of LCA (life cycle assessment), MFA (material flow analysis) and VCOM (value chain optional modelling)
- Anaerobic (AnO2) digestion of organic waste and sewage sludge is in most cases an effective means for drastically reducing the global warming potential (GWP), but regional differences play a significant role and it is important to substitute the most GWP intensive products
- With respect to terrestrial acidification potential (TAP) waste incineration is a better choice for both countries, and in the case of human toxicity potential (HTP) the situation is more complex
- There are major differences between GWP of treatment solutions in Norway and Poland. A treatment solution producing biomethane for fuel and dewatered bioresidual as biofertilizer, has the potential of avoiding a high amounts of GWP in Norway, but contributes to an increased impact relating to the substituted products in Poland. Conversely, it can be seen that electricity substitution is highly GWP beneficial in Poland, but has almost no effect on the Norwegian potential
Executive summaries of WP4 results
The work package is carried out with a focus on environmental life cycle assessment (LCA) of different technologies in value chains for resource recovery from mixed organic substrate feedstocks based on sewage sludge and organic wastes. The aim was to analyse the current context and technologies for such recovery opportunities, and their potential environmental impacts, with respect to policy and applications in Norway and Poland. At the core of this research, much work has been allocated to development and testing of quantitative LCA models, including comparison of system performance of case studies that represent different contexts regarding the nature of organic feedstocks, choice of treatment technologies, and final usage options of recovered products and by-products. Task 4.1 aimed to provide the needed scientific, policy and empirical basis for the following research in WP4. A state-of-the-art analysis was carried out on the current regulation, practice, statistics and relevant LCA literature with respect to sewages sludge and bio-waste generation and treatment in Norway and Poland. The emphasis was on current regulation and waste statistics, and on novel technologies and LCA impacts related to biogas production from different kinds of waste substrates. The state-of-the-art review (D4.1) begins by analysing the legal frameworks that influence organic waste treatment and biogas production in Norway and Poland. These legal frameworks are explored systematically according to the current process chains of organic waste and sludge collection, treatment and end-use. The legal situations in Norway and Poland differ in that Norway has a more substantial waste framework in place that leads to positive outcomes. Norway lacks a definitive, singular legal framework on biogas production but the sum of these organic waste treatment laws, most critically the landfill ban on all organic wastes, provides a cohesive organic waste treatment strategy. Poland, however, lacks both cohesive legal measures and strategy to treat organic wastes efficiently which results in poor organic waste utilization and high levels of landfilling. The positive is that Poland is bound to European Union (EU) regulations that have slowly pushed waste treatment options into legal discussions. These discussions are ongoing and will likely lead to positive changes in Poland in the future despite today’s lack of policy. Organic waste generation in both Norway and Poland is steadily increasing. The statistical evidence suggests that Norway and Poland are both utilizing greater amounts of organic waste than ever before. Norway has essentially eliminated organic waste to landfills while Poland has also seen large declines. Both Norway and Poland still have a much greater potential to produce biogas from current waste flows, which implies a need for more biogas infrastructure and waste separation. The common technologies and systems used to manage, treat and utilize waste products are summarized in the State-of-the-art review in a section on technologies. The technologies studies are sludge treatment, incineration, composting, anaerobic digestion, substrate mixes, co-digestion, post-digestion use and biogas upgrading technology. The conclusion is that while there are multiple technologies that can be used to treat organic wastes, there is no singular technology that can be used for all waste streams. Technology choice is thus dependent on local conditions and local needs. The final section of the review is an overview of other relevant studies on organic waste treatment and biogas production. The literature supports the environmental benefits of producing biogas from organic waste and using treated organic waste in land-use applications. Task 4.2 and 4.3 aimed at developing LCA models for the assessment of environmental impacts of technologies for treatment of sewage sludge and organic wastes, and focused on testing of such LCA models for a variety of cases and selected technology configurations. This included input data collection (using Ecoinvent LCI database and empirical data collection), for the calibration, testing, uncertainty and sensitivity analysis, and interpretation of LCA results. Since model development and testing in practice by requirement is an iterative process, the contents of these two tasks have been carried out in parallel, and as an integrated overall research activity, over a period of more than two years and with the involvement of 6 MSc students towards their final master’s theses at NTNU.
The modelling work have included the development of an overall systems definition, concluding on the systems boundaries and processes in value chains for recovery of energy and materials/nutrients from sewage sludge and organic wastes. An MSc thesis by Xu (2014) analysed sewage sludge recovery systems in an EU context, in perspectives of nutrients and energy recovery and environmental impacts. This study was based on literature data and an average European context of application, as a means to pinpoint key processes and variables for environmental impact contributions. A follow-up MSc thesis by Seldal (2014), on the other hand, studied the processes and technologies in a value chain case study for Oslo, with biogas production at the Romerike Biogassanlegg. This case study represents a system with the use of innovative (state-of-the-art) technologies for central optical sorting of organic fraction of municipal wastes and anaerobic fermentation and upgrading of biogas to biofuel used for transport. This study gave a detailed analysis of such a modern system, using a value-chain systems perspective in the analysis, and documented critical processes and variables for energy recovery efficiency, material recovery efficiency and environmental impacts in the system. The LCA-models by Xu and Seldal represent the first stage of LCA-modelling in the BioTEnMaRe project. On the basis of the above studies, a second stage of LCA modelling was started in 2014. Four MSc students collaborated on developing LCA models for different case contexts, however, by using one generic overall system definition and thereby one common overall LCA model structure. The aim of this research was to advance the LCA modelling approaches towards a tool that could be used for comparison across cases, for increased consistency when examining LCA results under different case conditions, different technologies, different end usage of products and by-products, and under different assumptions such as for the background energy system in a country. The tool was initially developed by use of Arda LCA, which is the in-house research tool for LCA at NTNU’s Industrial Ecology Programme. Later, during the spring semester 2015, a third stage of LCA modelling was carried out in the project, where the four MSc students at NTNU refined the LCA models towards a new set of tools developed in Excel and SimaPro. This was done to control how LCA modelling results aligned with or deviated from the second stage results, and for quality assessment and consistency checking with what is considered to be the industrial LCA-standard; i.e. SimaPro. Three MSc theses collaborated on development and joint use of a common MFA-model in Excel (for mass-balance consistency in mass and energy flows in waste treatment systems) and a common LCA-model in SimaPro (for environmental impact assessment). This model was used by Hegg (2015) to study resource recovery and environmental impacts at the case study “The Magic Factory” in Sandefjord, Norway. This is a case study with little use of sewage sludge, but use of different sources of organic wastes and manure, for biogas production, with biogas upgrading to biofuel for transport and digestate for use in agriculture. Saxegård (2015) used the model for analysis of different cases in a Norwegian applied context, where each case typically included a combination of feedstock sources, technologies and end-use applications of recovered products and by-products. Danielsson (2015) made use of the same LCA-model to examine the resource recovery efficiency and environmental impacts from biogas and biofuel production from organic waste substrates under Danish and Polish conditions. This geographic scope was chosen to supplement the other studies that had a Norwegian scope, and with a Danish case study included as this was considered closer to the Polish context. Solberg (2015) used a slightly different LCA-model for the testing at a case in Bergen, Norway, representing a new biogas production facility mainly treating sewage sludge collected from different wastewater treatment plants in Bergen. Finally, a fourth stage of the LCA development and testing process was done in 2016. This included final refinement of the MFA tool, including a database of input values for all system variables for one generic case in Norway and one generic case in Poland. It also included translating the LCA tool from the academic to the professional version of SimaPro, and testing the sensitivities for the analyses from both cases. This final translation and database development was carried out by Østfoldforsk, acting as subcontractor to NTNU, with Saxegård as LCA analyst. The results of the work in Task 4.2 and 4.3 are published in six MSc thesis reports at NTNU (Xu 2015, Seldal 2015, Saxegaard 2015, Hegg 2015, Danielsson 2015 and Solberg 2015) and the conclusions from the last stage of the LCA development and testing are given in D4.2 (Brattebø, Saxegård and Baxter 2016). Task 4.4 brings together a synthesis of research findings from Task 4.1, 4.2 and 4.3, towards providing a short summary aiming at a policy ranking of different choices in treatment systems for resource recovery from sewage sludge and organic wastes. The choices include opportunities and priorities for co-treatment of different types and mixes of organic waste substrates, different treatment technologies (focusing on biogas production versus incineration and composting) and on different end usage opportunities of products and by-products. The conclusion is that the current trend of biogas production from mixed feedstock of organic wastes, and upgrading of biogas for use as fuel in transport, as today often seen in Norwegian new cases, seems to be the number 1 ranked technology priority. The resources allocated to WP4 are mainly used for research working hours at NTNU, subcontracting of technical assistance from Østfoldforskning AS, and travels. Not all budgets for other costs and indirect costs are used, due to less need for laboratory tests and travels than initially anticipated.