Karlsson Hanna, Ahlgren Serina, Sandgren Mats, Passoth Volkmar, Wallberg Ola, Hansson Per-Anders
Department of Energy and Technology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Department of Molecular Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Biotechnol Biofuels. 2017 Sep 13;10:217. doi: 10.1186/s13068-017-0907-9. eCollection 2017.
Use of bio-based diesel is increasing in Europe. It is currently produced from oilseed crops, but can also be generated from lignocellulosic biomass such as straw. However, removing straw affects soil organic carbon (SOC), with potential consequences for the climate impact of the biofuel. This study assessed the climate impacts and energy balance of biodiesel production from straw using oleaginous yeast, with subsequent biogas production from the residues, with particular emphasis on SOC changes over time. It also explored the impact of four different scenarios for returning the lignin fraction of the biomass to soil to mitigate SOC changes. Climate impact was assessed using two methods, global warming potential (GWP) and a time-dependent temperature model (∆T ) that describes changes in mean global surface temperature as a function of time or absolute temperature change potential (AGTP).
Straw-derived biodiesel reduced GWP by 33-80% compared with fossil fuels and primary fossil energy use for biodiesel production was 0.33-0.80 MJ/MJ, depending on the scenario studied. Simulations using the time-dependent temperature model showed that a scenario where all straw fractions were converted to energy carriers and no lignin was returned to soil resulted in the highest avoided climate impact. The SOC changes due to straw removal had a large impact on the results, both when using GWP and the time-dependent temperature model.
In a climate perspective, it is preferable to combust straw lignin to produce electricity rather than returning it to the soil if the excess electricity replaces natural gas electricity, according to results from both GWP and time-dependent temperature modelling. Using different methods to assess climate impact did not change the ranking between the scenarios, but the time-dependent temperature model provided information about system behaviour over time that can be important for evaluation of biofuel systems, particularly in relation to climate target deadlines.
在欧洲，生物柴油的使用正在增加。目前它由油料作物生产，但也可由木质纤维素生物质（如秸秆）产生。然而，移除秸秆会影响土壤有机碳（SOC），这可能对生物燃料的气候影响产生潜在后果。本研究评估了利用产油酵母从秸秆生产生物柴油以及随后从残渣生产沼气的气候影响和能量平衡，特别强调了SOC随时间的变化。它还探讨了将生物质的木质素部分返还土壤以减轻SOC变化的四种不同情景的影响。使用两种方法评估气候影响，即全球变暖潜能值（GWP）和一个随时间变化的温度模型（∆T），该模型描述了全球平均地表温度随时间的变化或绝对温度变化潜能值（AGTP）。
与化石燃料相比，秸秆衍生的生物柴油使GWP降低了33 - 80%，生物柴油生产的一次化石能源使用量为0.33 - 0.80兆焦/兆焦，具体取决于所研究的情景。使用随时间变化的温度模型进行的模拟表明，所有秸秆部分都转化为能量载体且没有木质素返还土壤的情景导致最大的气候影响避免量。无论是使用GWP还是随时间变化的温度模型，因移除秸秆导致的SOC变化对结果都有很大影响。
从气候角度来看，根据GWP和随时间变化的温度模型的结果，如果多余的电力替代天然气发电，燃烧秸秆木质素来发电比将其返还土壤更可取。使用不同方法评估气候影响并没有改变情景之间的排名，但随时间变化的温度模型提供了有关系统随时间行为的信息，这对于评估生物燃料系统可能很重要，特别是在与气候目标期限相关的方面。
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