Byrne Eoin, Kovacs Krisztina, van Niel Ed W J, Willquist Karin, Svensson Sven-Erik, Kreuger Emma
1Division of Applied Microbiology, Dept. of Chemistry, Lund University, PO Box 124, 221 00 Lund, Sweden.
2Dept. of Chemical Engineering, Lund University, PO Box 124, 221 00 Lund, Sweden.
Biotechnol Biofuels. 2018 Oct 11;11:281. doi: 10.1186/s13068-018-1280-z. eCollection 2018.
Current EU directives demand increased use of renewable fuels in the transportation sector but restrict governmental support for production of biofuels produced from crops. The use of intercropped lucerne and wheat may comply with the directives. In the current study, the combination of ensiled lucerne ( L.) and wheat straw as substrate for hydrogen and methane production was investigated. Steam-pretreated and enzymatically hydrolysed wheat straw [WSH, 76% of total chemical oxygen demand (COD)] and ensiled lucerne (LH, 24% of total COD) were used for sequential hydrogen production through dark fermentation and methane production through anaerobic digestion and directly for anaerobic digestion. Synthetic co-cultures of extreme thermophilic species adapted to elevated osmolalities were used for dark fermentation.
Based on 6 tested steam pretreatment conditions, 5 min at 200 °C was chosen for the ensiled lucerne. The same conditions as applied for wheat straw (10 min at 200 °C with 1% acetic acid) would give similar sugar yields. Volumetric hydrogen productivities of 6.7 and 4.3 mmol/L/h and hydrogen yields of 1.9 and 1.8 mol/mol hexose were observed using WSH and the combination of WSH and LH, respectively, which were relatively low compared to those of the wild-type strains. The combinations of WSH plus LH and the effluent from dark fermentation of WSH plus LH were efficiently converted to methane in anaerobic digestion with COD removal of 85-89% at organic loading rates of COD 5.4 and 8.5 g/L/day, respectively, in UASB reactors. The nutrients in the combined hydrolysates could support this conversion.
This study demonstrates the possibility of reducing the water addition to WSH by 26% and the phosphorus addition by 80% in dark fermentation with species, compared to previous reports. WSH and combined WSH and LH were well tolerated by osmotolerant co-cultures. The yield was not significantly different when using defined media or hydrolysates with the same concentrations of sugars. However, the sugar concentration was negatively correlated with the hydrogen yield when comparing the results to previous reports. Hydrolysates and effluents from dark fermentation can be efficiently converted to methane. Lucerne can serve as macronutrient provider in anaerobic digestion. Intercropping with wheat is promising.
当前欧盟指令要求在交通运输领域增加可再生燃料的使用，但限制政府对作物生产生物燃料的支持。间作苜蓿和小麦的使用可能符合这些指令。在本研究中，研究了青贮苜蓿（L.）和小麦秸秆作为产氢和产甲烷底物的组合。蒸汽预处理和酶解的小麦秸秆[WSH，占总化学需氧量（COD）的76%]和青贮苜蓿（LH，占总COD的24%）用于通过暗发酵顺序产氢和通过厌氧消化产甲烷，并直接用于厌氧消化。使用适应高渗透压的极端嗜热菌种的合成共培养物进行暗发酵。
基于6种测试的蒸汽预处理条件，选择200℃下5分钟用于青贮苜蓿。与用于小麦秸秆的条件（200℃下10分钟，添加1%乙酸）相同的条件会产生相似的糖产量。使用WSH以及WSH和LH的组合时，体积产氢率分别为6.7和4.3 mmol/L/h，氢产率分别为1.9和1.8 mol/mol己糖，与野生型菌株相比相对较低。WSH加LH以及WSH加LH暗发酵的流出物在UASB反应器中通过厌氧消化有效地转化为甲烷，在COD负荷率分别为5.4和8.5 g/L/天的情况下，COD去除率为85 - 89%。混合水解产物中的营养物质可以支持这种转化。
本研究表明，与之前的报道相比，在使用菌种进行暗发酵时，WSH的加水量可减少26%，磷添加量可减少80%。耐渗透压共培养物对WSH以及WSH和LH的组合耐受性良好。使用定义培养基或相同糖浓度的水解产物时，产率没有显著差异。然而，将结果与之前的报道进行比较时，糖浓度与氢产率呈负相关。暗发酵的水解产物和流出物可以有效地转化为甲烷。苜蓿可以作为厌氧消化中的大量营养物质提供者。与小麦间作很有前景。
