Effects of pH on ex-situ biomethanation with hydrogenotrophic methanogens under thermophilic and extreme-thermophilic conditions

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Variations in methane yield and microbial community profiles in the rumen of dairy cows as they pass through stages of first lactation

Considerable interest exists both from an environmental and economic perspective in reducing methane emissions from agriculture. In ruminants, CH₄ is produced by a complex community of microorganisms that is established in early life but can be influenced by external factors such as feed. Although CH₄ emissions were thought to be constant once an animal reached maturity, recent studies have shown that CH₄ yield significantly increases from early to late lactation in dairy cows. The aim of this study was to test the hypothesis that increases in CH₄ yield over the lactation cycle are related to changes in rumen microbial community structure. Nine cows were monitored throughout their first lactation cycle. Methane and dry matter intake were measured to calculate CH₄ per dry matter intake (CH₄ yield) and ruminal fluid was collected during early, mid, and late lactation. A significant difference in bacterial and archaeal community structure during early and late lactation was observed. Furthermore, when ruminal short-chain fatty acid concentrations were measured, the ratio of acetate and butyrate to propionate was significantly higher in late lactation compared with early lactation. Propionate concentrations were higher in cows with low CH₄ yield during late lactation, but no differences were observed in bacterial or archaeal community structures. Prevotella dominated the rumen of cows followed by Succinclasticum; Treponema, Fibrobacter, Ruminococcus, and Bifidobacterium were also in high abundance relative to other bacterial genera. In general, positive correlations were stronger between the most relatively abundant bacterial genera and acetate and butyrate concentrations in the cows with high CH₄ and weaker between these genera and propionate concentration. This study indicates that increased CH₄ yield in late lactation is reflected in significant changes in microbial community structure.     

基于高通量测序的浓香型白酒窖池古菌群落结构分析

本试验利用罗氏GS junior高通量测序平台分析了30年窖龄的浓香型白酒窖池窖泥古菌群落结构,结果发现:3口窖池样品共获得8706条有效序列,282个OTUs分类;样品中古菌的Shannon曲线值在4~5之间就趋于稳定,Chao曲线的值随着序列数的增加而增长。窖泥中古菌类群主要集中在Euryarchaeota(广古菌门)下的Thermoplasmata class(热原体纲)中的Thermoplasmataceae(热原体科),Methanobacteria class(甲烷杆菌纲)中的Methanobacteriaceae(甲烷杆菌科),Methanococci class(甲烷球菌纲)中的Methanomicrobiaceae(甲烷微菌科)、Methanocorpusculaceae(甲烷八叠球菌科)和Methanosarcinaceae(甲烷粒菌科);Saccharococcus sp.和WCHD3-02也有检测到。其中Thermoplasmataceae和Methanobacteriaceae占绝对优势,分别为39%和27%,其它菌类Methanomicrobiaceae占9%、Methanosarcinaceae占7%和Methanocorpusculaceae占4%、Saccharococcus sp.(糖球菌属)占1%和WCHD3-02占1%,unclassified序列占12%;对甲烷菌类进行深入分析,发现了Methanoculleus marisnigri strain、Methanoculleus bourgensis strain、Methanosarcina siciliae strain、Methanobacterium、Methanocorpusculum和Methanomicrobia等种属的菌种。     

产甲烷菌高度紧密子网络分析

为了从系统水平上阐明嗜热菌的耐热机制,并指导嗜热菌在工业生产上的进一步应用,以产甲烷菌的代谢网络作为研究对象,从研究代谢网络的拓扑结构以及高度紧密子网络出发,探索常温产甲烷菌Methanosarcina acetivorans(M.acetivorans)和嗜热产甲烷菌Methanopyrus kandleri(M.kandleri)之间的代谢网络的耐热性的差异。实验结果发现常温产甲烷菌M.acetivorans最紧密的9-核和嗜热产甲烷菌M.kandleri最紧密的7-核分别包含27和19个酶。其中嗜热产甲烷菌M.kandleri网络中最紧密的7-核被分成2个子网,一个子网中的酶节点刚好是2个产甲烷菌所共同的酶,而另一个子网络中的酶是嗜热产甲烷菌M.kandleri 7-核所特有的酶,这些特有的酶全部与酪氨酸的合成有关。     

Digestion of pre‐treated food waste in a hybrid anaerobic solid–liquid (HASL) system

The hybrid anaerobic solid–liquid (HASL) system was developed to be used in industrial‐scale operations to minimize the amount of food waste for disposal in Singapore. Thermal pre‐treatment of food waste at 70 °C for 2 h (experiment E1) or at 150 °C for 1 h (experiment E2) facilitated the hydrolytic and acidogenic processes in the acidogenic reactor and methanogenesis in the methanogenic reactor in the HASL system. The highest dissolved chemical oxygen demands in the effluents from the acidogenic reactors were 17 575, 19 980 and 24 235 mg dm^?3 in the control with food waste without thermal pre‐treatment and experiments E1 and E2, respectively. The maximum concentrations of methanogens in the methanogenic reactor were 2.3 × 10⁷, 3.8 × 10⁷, 4.3 × 10⁷ cells cm^?3 for the control and experiments E1 and E2, respectively. However, the performances of the methanogenic phase in terms of specific activity of methanogens did not differ significantly for the control and experiments E1 and E2. Use of thermally pre‐treated food waste halved the time to produce the same quantity of methane in comparison with anaerobic digestion of fresh food waste. The fluorescent measurements of co‐enzyme F₄₂₀ and oligonucleotide probe Arc915 specifically bound (hybridized) with 16S rRNA were used for monitoring of methanogens during anaerobic digestion of food waste. There was a linear correlation between these parameters and the concentration of methanogens in the effluent from the methanogenic reactor. Copyright © 2005 Society of Chemical Industry     

Nickel stimulation of anaerobic digestion

An acetate-enriched methanogenic culture was assayed for nutritional stimulation by nickel in combination with other inorganic and organic nutrients, i.e. iron, cobalt, yeast extract, riboflavin and vitamin B₁₂. Acetate was automatically maintained at 2–3 g l⁻¹ by a pH Stat system so that substrate was not limiting. In the absence of nickel, the specific acetate utilization rates were in the range of 2–4.6 g acetate g⁻¹ VSS day⁻¹. In the presence of nickel, this rate was as high as 10 and when both nickel and yeast extract were supplemented this rate temporarily increased to 12–15 g acetate g⁻¹ VSS day⁻¹ . The maximum acetate utilization rate was observed to be 51 g l⁻¹ day⁻¹ as compared to 3.3 g l⁻¹ day⁻¹ for conventional high-rate digestion. Daily phosphate additions were required to sustain these high acetate utilization rates. An acetate utilization rate of 20–30 g l⁻¹ day⁻¹ was maintained for over 25 days. Microscopic examination of the culture revealed a predominance of a sarcina whenever stimulation was noted.     

厌氧消化过程氨抑制解除技术研究进展

厌氧消化在处理有机废物的同时可产生大量的甲烷资源,是能源可持续发展的重要处理技术。作为微生物生长的营养物质之一,氨在厌氧消化过程中发挥重要作用,然而高浓度氨会抑制微生物活性,造成厌氧消化系统的失效。在总结国内外研究进展的基础上,讨论了氨抑制的形成机理及氨对产甲烷菌的抑制作用,并分别从氨浓度和微生物两个角度总结了当前解除氨抑制的技术和方法,为厌氧消化的工程应用和进一步氨抑制研究提供参考和建议。     

The use of hybrid anaerobic solid–liquid (HASL) system for the treatment of lipid‐containing food waste

The hybrid anaerobic solid–liquid (HASL) system was a modified two‐phase anaerobic digester developed for bioconversion of food waste. The aim of this study was to estimate the feasibility of the HASL system for the treatment of food waste with a high content of lipids. The presence of lipids in food waste increased the energy value of nutrients but could inhibit growth of methanogens. The positive effect of lipids on the performance of anaerobic digestion dominated when the contents of lipids were in the range from 20 to 30% of total solids of food waste. Lipid contents of 40% diminished the production of volatile fatty acids in the acidogenic reactor as well as biogas production and the concentration of total bacteria and methanogens in the methanogenic reactor. Therefore, the HASL system can be used for the treatment of lipid‐containing food wastes if the lipid content is below 40% of total solids. Copyright © 2005 Society of Chemical Industry     

pH对UASB运行效能及产甲烷互营菌群的影响

研究产甲烷互营菌群对pH变化的响应,对于寻求提高有机废水厌氧生物处理效能的策略具有重要意义.以处理制糖废水的升流式厌氧污泥床(UASB)反应器的运行为基础,考察不同pH对反应器运行效能及产甲烷互营菌群的影响.结果表明,在进水COD 20 000 mg·L-、HRT 8 h的条件下,当进水pH分阶段由6.9降至5.4时,UASB系统的pH随之从6.8 ～7.4下降至5.7 ～6.7,导致COD去除率降低了23.3％,出水中残留丙酸提高了3.9倍.聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)分析结果表明,产氢产乙酸菌群在UASB中的多样性显著低于产甲烷菌群,其分布和优势度受pH降低的影响显著.以Eub 19(Pelotomaculum)为代表的食丙酸产氢产乙酸菌在偏酸环境中的优势度明显减弱,而食乙酸产甲烷菌及部分食氢产甲烷菌对pH下降响应并不显著,且随着pH下降,耐酸的食氢产甲烷菌Methanobacterium ferruginis和Uncultured Methanobrevibacter的优势度逐渐增强.由此可见,与产甲烷菌群相比,UASB系统中的产氢产乙酸菌群对pH的变化更加敏感.     

丙酸质量浓度对丙酸富集培养物降解特性的影响

为阐明丙酸质量浓度对厌氧生物处理系统中丙酸降解特性的影响,研究了不同丙酸质量浓度条件下丙酸富集培养物的降解特性．以丙酸为唯一碳源,通过15代的传代培养富集到一个中温互营丙酸氧化菌群(包括丙酸氧化菌和产甲烷菌)．聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)指纹分析结果表明,该富集培养物中的丙酸氧化菌为Syntrophobacter,而嗜氢产甲烷菌和嗜乙酸产甲烷菌分别为Methanobacterium和Methanosaeta．在污泥接种量为0.81 g／L条件下,当丙酸质量浓度为1 000~2 000 mg／L时,丙酸能够被该富集培养物快速降解;而当丙酸质量浓度为2 500~3 000 mg／L时,丙酸降解和乙酸的转化均受到一定程度的抑制,但随着培养时间的延长,该抑制作用逐步解除．较高的丙酸质量浓度(≥2 500 mg／L)能够对丙酸氧化菌产生可逆性抑制作用．