Anaerobic digestion (AD) can play an important role in achieving renewable goals set within the Netherlands which strives for 40 PJ bio-energy in the year 2020. This research focusses on reaching this goal with locally available biomass waste flows (e.g. manures, grasses, harvest remains, municipal organic wastes). Therefore, the bio-energy yields, process efficiency and environmental sustainability are analyzed for five municipalities in the northern part Netherlands, using three utilization pathways: green gas production; combined heat and power; and waste management. Results indicate that the Dutch goal cannot be filled through the use of local biomass waste streams, which can only reach an average of 20 PJ. Furthermore renewable goals and environmental sustainability do not always align. Therefore, understanding of the absolute energy and environmental impact of biogas production pathways is required to help governments form proper policies, to promote an environmentally and social sustainable energy system.
Anaerobic digestion (AD) can play an important role in achieving the renewable energy goals set within the European Union. Within this article the focus is placed on reaching the Dutch local renewable production goal set for the year 2020 with locally available biomass waste flows, avoiding intensive farming and long transport distances of biomass and energy carriers. The bio-energy yields, efficiency and environmental sustainability are analyzed for five municipalities in the northern part of the Netherlands, using three utilization pathways: green gas production, combined heat and power, and waste management. Literature has indicated that there is sufficient bio-energy potential in local waste streams to reach the aforementioned goal. However, the average useful energy finally produced by the AD production pathway is significantly lower, often due to poor quality biomass and difficult harvesting conditions. Furthermore, of the potential bio-energy input in the three utilization pathways considered in this article, on average: 73% can be extracted as green gas; 57% as heat and power; and 44% as green gas in the waste management pathway. This demonstrates that the Dutch renewable production goal cannot be reached. The green gas utilization pathway is preferable for reaching production goals as it retains the highest amount of energy from the feedstock. However, environmental sustainability favors the waste management pathway as it has a higher overall efficiency, and lower emissions and environmental impacts. The main lessons drawn from the aforementioned are twofold: there is a substantial gap between bio-energy potential and net energy gain; there is also a gap between top–down regulation and actual emission reduction and sustainability. Therefore, a full life cycle-based understanding of the absolute energy and environmental impact of biogas production and utilization pathways is required to help governments to develop optimal policies serving a broad set of sustainable objectives. Well-founded ideas and decisions are needed on how best to utilize the limited biomass availability most effectively and sustainably in the near and far future, as biogas can play a supportive role for integrating other renewable sources into local decentralized energy systems as a flexible and storable energy source.
Biogas produced through Anaerobic Digestion can be seen as a flexible and storable energy carrier. However, the environmental sustainability and efficiency of biogas production is not fully understood. Within this article the use, operation, structure, validation, and results of a model for the environmental assessment of anaerobic biogas production pathways is discussed. The (Excel) BioGas Simulator or EBS model is capable of calculating the economic cost, efficiency, carbon footprint, and sustainability of small scale anaerobic digestion biogas production pathways (from 2000 up to 50000 ton/a biomass input). The results from the model are expressed in four main indicators: the economic cost in Net Present Value (NPV), the efficiency in Process Energy Returned On Invested or (P)EROI, the carbon footprint in Global Warming potential 100 year scale (GWP100), and the environmental impact in EcoPoints. The economic indicator is given in Euros in Net Present Value over a period of 25 years, the other indicators are given per Giga Joule of energy produced (e.g. kgCO2eq/GJ). The EBS model is based on a clear methodology, structured around the modular approach, energy and material flow analysis, and life cycle analysis. The modular approach separates the biogas production pathway into individual physical processes, which makes the model more transparent, flexible in use, and programmable with different settings. The aforementioned allows the research of several aspects of the biogas production pathway. Furthermore, the indication of sustainability in four clear indicators gives an understandable reference for comparison with other scenarios. Overall, the EBS model can help give insight on the sustainability of specific biogas production pathways and help indicate options for improvement. Results from the model indicate that from an energy efficiency and sustainability point of view, the anaerobic digestion process should be utilized for treating locally available waste feedstocks with the added advantage of producing energy, which should preferentially be used internally for powering the waste treatment process.
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