Potential role of sulfide precipitates in direct interspecies electron transfer facilitation during anaerobic digestion of fish waste

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Stimulating biogas production from steam-exploded birch wood using Fenton reaction and fungal pretreatment

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Greenhouse gas balances in Zero Emission Buildings – Electricity conversion factors revisited

Reduction of energy use and GHG emissions in the building sector is a high priority. The EU 2050 roadmap that was established in 2010, states that to achieve a global warming of less than 2°C in this century, Europe should reduce its GHG emissions by 80 % by 2050, using 1990 emissions as the reference. The roadmap shows that it is the power sector and the building sector that face the most severe reductions, with emission reductions of around 90%. The Norwegian research centre for Zero Emission Buildings (ZEB) was established in 2008, with the objective to "develop competitive products and solutions for existing and new buildings that will lead to market penetration of buildings that have zero GHG emissions of greenhouse gases related to their production, operation and demolition" (www.zeb.no). According to the ZEB Centre, a building may be defined as a Zero Emission Building when all the GHG emissions from the entire life cycle of the building are compensated by GHG emission credits from the generation of renewable energy. However, the calculation of the life time compensation of greenhouse gas emissions in ZEBs involves a number of difficult issues, and has been subject to extensive discussions among the ZEB researchers and among different professions. A central issue is the methodology for calculating the carbon emission credits for electricity use and generation, and how the generation of renewable energy in the operation phase should be valued with respect to offsetting the embodied carbon emissions from the production of the building. Since buildings have a life time of several decades, this involves the stipulation of the future carbon intensity of grid electricity. Another issue is how to balance the historic emissions from the production of materials against the future GHG emission offset of the renewable energy surplus from the operation phase of the building. These issues are elaborated on in the report. It includes a review of previous work and methods that have been applied in the ZEB Centre, with focus on the calculation of embodied emissions and the conversion factor for electricity in the operation phase. It also gives an overview of different methods and approaches for establishing emission credits from electricity use and generation, as well as related policy measures for GHG abatement. It discusses how to balance historic GHG emissions vs future emission credits, and challenges of the exchange of electricity between ZEBs and the grid. A key challenge of the center has been to produce innovations within the inherent space of uncertainty given by the related frontiers of the research. Thus, a research strategy for the ZEB centre has been to maximize the incentives for the development of different solutions that reduce the overall GHG emissions connected to a building. If the GHG emission credits favour only one solution to reach a zero emission balance, then the result may be easier to reach in the present. However, given the fundamental uncertainty of future developments, preparing only for one route to reach the goal is a risky navigational strategy. On the other hand, if the conversion factor is chosen in a way so that a zero emission balance is impossible to reach in the present no matter which solution is chosen, then interesting research may be the result, but the industry will be very unlikely to participate in the construction of an “impossible” building. Thus, on must find a balance between assumptions about the future that discourage innovation completely and assumptions that lead to only one innovation. The experiences from the pilot building projects within the ZEB center show that reaching the highest levels of ambition for ZEB is very challenging, given the boundary conditions and the applied CO2-factor for grid electricity. The analyses and discussion indicate that the CO2-factor that have been used in the ZEB pilot projects probably does not “favor” energy measures on ZEBs compared to other measures for CO2-mitigation. Nevertheless, such a challenging CO2-factor have promoted innovation in that it has spurred the teams to reach further than they otherwise would have done, resulting in new solutions being implemented and tested out. As such, the chosen CO2-factor may be said to have served its purpose.publishedVersio

Lessons learned from an experimental campaign on promoting energy content of renewable biogas by injecting H2 during anaerobic digestion

Direct injection of H2 to an anaerobic reactor enables biological fixation of CO2 into CH4 (biomethanation) and consequently boosts methane content in the produced biogas. However, there has been only a small amount of literature reporting results on this technique in a continuous reactor framework to date. To fill this gap, the present study devoted an experimental work to direct H2 addition to a fed-batch semi-continuous reactor, where the injected H2 concentration increased gradually (~3–30 mmol), spanning a moderate operational period of about 70 days. As the results revealed, the reactor continued anaerobic operation for each level of H2 dosing and produced an average methane content in the biogas ranging between 65% and 72%. The exhibited biogas upgrading trend appeared to be under-developed, and thereby suggests the need for further research

Greenhouse gas balances in Zero Emission Buildings – Electricity conversion factors revisited

Reduction of energy use and GHG emissions in the building sector is a high priority. The EU 2050 roadmap that was established in 2010, states that to achieve a global warming of less than 2°C in this century, Europe should reduce its GHG emissions by 80 % by 2050, using 1990 emissions as the reference. The roadmap shows that it is the power sector and the building sector that face the most severe reductions, with emission reductions of around 90%. The Norwegian research centre for Zero Emission Buildings (ZEB) was established in 2008, with the objective to "develop competitive products and solutions for existing and new buildings that will lead to market penetration of buildings that have zero GHG emissions of greenhouse gases related to their production, operation and demolition" (www.zeb.no). According to the ZEB Centre, a building may be defined as a Zero Emission Building when all the GHG emissions from the entire life cycle of the building are compensated by GHG emission credits from the generation of renewable energy. However, the calculation of the life time compensation of greenhouse gas emissions in ZEBs involves a number of difficult issues, and has been subject to extensive discussions among the ZEB researchers and among different professions. A central issue is the methodology for calculating the carbon emission credits for electricity use and generation, and how the generation of renewable energy in the operation phase should be valued with respect to offsetting the embodied carbon emissions from the production of the building. Since buildings have a life time of several decades, this involves the stipulation of the future carbon intensity of grid electricity. Another issue is how to balance the historic emissions from the production of materials against the future GHG emission offset of the renewable energy surplus from the operation phase of the building. These issues are elaborated on in the report. It includes a review of previous work and methods that have been applied in the ZEB Centre, with focus on the calculation of embodied emissions and the conversion factor for electricity in the operation phase. It also gives an overview of different methods and approaches for establishing emission credits from electricity use and generation, as well as related policy measures for GHG abatement. It discusses how to balance historic GHG emissions vs future emission credits, and challenges of the exchange of electricity between ZEBs and the grid. A key challenge of the center has been to produce innovations within the inherent space of uncertainty given by the related frontiers of the research. Thus, a research strategy for the ZEB centre has been to maximize the incentives for the development of different solutions that reduce the overall GHG emissions connected to a building. If the GHG emission credits favour only one solution to reach a zero emission balance, then the result may be easier to reach in the present. However, given the fundamental uncertainty of future developments, preparing only for one route to reach the goal is a risky navigational strategy. On the other hand, if the conversion factor is chosen in a way so that a zero emission balance is impossible to reach in the present no matter which solution is chosen, then interesting research may be the result, but the industry will be very unlikely to participate in the construction of an “impossible” building. Thus, on must find a balance between assumptions about the future that discourage innovation completely and assumptions that lead to only one innovation. The experiences from the pilot building projects within the ZEB center show that reaching the highest levels of ambition for ZEB is very challenging, given the boundary conditions and the applied CO2-factor for grid electricity. The analyses and discussion indicate that the CO2-factor that have been used in the ZEB pilot projects probably does not “favor” energy measures on ZEBs compared to other measures for CO2-mitigation. Nevertheless, such a challenging CO2-factor have promoted innovation in that it has spurred the teams to reach further than they otherwise would have done, resulting in new solutions being implemented and tested out. As such, the chosen CO2-factor may be said to have served its purpose

Digitalization of colourimetric sensor arrays for volatile fatty acid detection in anaerobic digestion

During the process of converting the organic matter into methane, many volatile fatty acids (VFAs) are produced during acidogenesis and acetogenesis phases of the process. The main VFAs of interest are acetic acid, butyric acid and propionic acid. Although the production of these VFAs are essential for the production of methane, they also play an inhibitory role for many of the organisms involved in the production of biogas. As a consequence, the levels of VFAs produced in an anaerobic digester must be monitored. Current methodologies for VFA monitoring are either unspecific, or costly. Therefore, the development of a sensor method that is specific to the different VFAs, while maintaining a low cost, will facilitate the lowering of biogas production, as well as avoiding the costly biological collapse of the whole biogas production process. Here, an array of coloured dyes (colourimetric array) has been assessed for their ability to detect low concentrations of VFAs within the digestate during biogas production. This methodology lays the foundation for the development of a sensor system for use in biogas plants and could also be expanded to detect many other parameters within the biogas production process

Carbohydrate Yield and Biomethane Potential from Enzymatically Hydrolysed Saccharina latissima and Its Industrial Potential

The demand for fuel for utilisation of machinery and transport has culminated in large amounts of fossil fuel usage in the last century. The environmental dangers attached with the usage of fossil fuels have created a large demand for alternative sources of fuels. There is an array of polysaccharides contained within macroalgae, such as mannitol, cellulose and laminarin. These polysaccharides have potential for production of alternative biofuels; however, they are not easily accessible for biological digestion. By pretreatment of macroalgae with enzymes, these polysaccharides may be easier to access by microbes, allowing effective utilization in anaerobic digestion. Saccharina latissima, available in abundance on the Norwegian coast line, is a brown macroalgae with a high level of carbohydrates. This study assesses the ability for utilisation of enzymatically pre-treated Saccharina latissima for production of biogas through anaerobic digestion. The harvested Saccharina latissima was analysed to contain 30.11 ± 2.30 g of reducing sugars per 100 g of dry sample upon enzymatic hydrolysis. This was able to yield 459 ± 30 mL per gVS of biogas through anaerobic digestion, with a methane content of 56%. This suggests a biomethane potential of 1760 m3 per ha of productive sea floor growing Saccharina latissima. An evaluation of this process has been performed to demonstrate the industrial potential of Saccharina latissima in biogas production

Yield improvements in anaerobic digestion of lignocellulosic feedstocks

The new EU bioenergy sustainability criteria demonstrate that bioenergy sustainability can be a challenge (Schlegel and Kaphengst, 2007). In 1990s, the energy crops were the main source for biogas production in Europa; however, their competition with food production led these sources to be phased out as sustainable renewables. This makes alternative abundant bioenergy resources such as lignocellulosic materials increasingly interesting. Anaerobic digestion (AD) is a suitable waste management method in which renewable bioenergy can be produced from different feedstocks including lignocellulosic material. Even though the lignocellulose is a biomass with high energy content, it has rigid structure to be used in AD. To overcome this, a pre-treatment method is needed for the complete extraction of the energy in AD. Several pre-treatment methods have shown to be very effective independent of the type of lignocellulose in the biomass. Apart from assessing physical characteristics of lignocellulosic materials and their biogas production potential before and after pre-treatment, this review assesses the developed pre-treatment methods for lignocellulosic feedstocks for AD, and highlights the effectiveness, limitations and challenges of these techniques. This review discusses the possible strategies to implement a lignocellulosic-based biogas plant with optimised net cost and energy consumption through improving process design. Even though high energy yields from the harvested biomass is economically desirable, the solutions with the highest possible energy yield are not necessarily the ecologically best ones. Thermal pre-treatment appears to give the highest increases in methane yields, but the proper balance between high yields and the ecological fate of non-digested carbon containing materials (i.e. lignin in the AD digestate) needs to be further studied. Heat recovery and process integration will be needed to reduce inherent energy consumption in thermal pre-treatmen

Optimization of an Absorption-Based Biogas Upgrading and Liquefaction Process

The present work proposes a methodology for optimization of a liquefied biomethane (LBM) production plant. The LBM production plant comprises amine-based absorption upgrading followed by a single expander refrigeration cycle. The processes were modeled using Aspen HYSYS® and optimized through a Sequential Quadratic Programming algorithm. Any changes in the operating conditions of the upgrading process will affect the cooling demand in the liquefaction, while the opposite is not true. Based on this, a sequential optimization approach starting with the upgrading process is proposed. In order to accommodate the connection between the processes, different objective functions were formulated for the sequential optimization approach. The results from the sequential approach were compared with an overall optimization approach, where the entire LBM plant was optimized simultaneously. The results indicate that the same solution was obtained both for the sequential approach and the simultaneous approach. For the sequential approach, however, the best result was observed when the interaction between the upgrading and liquefaction processes was accounted for by considering the effect of the upgrading process on the exergy requirement in the liquefaction process

Molecular Microbial Community Analysis as an Analysis Tool for Optimal Biogas Production

The microbial diversity in anaerobic digestion (AD) is important because it affects process robustness. High-throughput sequencing offers high-resolution data regarding the microbial diversity and robustness of biological systems including AD; however, to understand the dynamics of microbial processes, knowing the microbial diversity is not adequate alone. Advanced meta-omic techniques have been established to determine the activity and interactions among organisms in biological processes like AD. Results of these methods can be used to identify biomarkers for AD states. This can aid a better understanding of system dynamics and be applied to producing comprehensive models for AD. The paper provides valuable knowledge regarding the possibility of integration of molecular methods in AD. Although meta-genomic methods are not suitable for on-line use due to long operating time and high costs, they provide extensive insight into the microbial phylogeny in AD. Meta-proteomics can also be explored in the demonstration projects for failure prediction. However, for these methods to be fully realised in AD, a biomarker database needs to be developed